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microwatt/predecode.vhdl

602 lines
26 KiB
VHDL
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Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
-- Instruction pre-decoder for microwatt
-- One cycle latency. Does 'WIDTH' instructions in parallel.
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
library work;
use work.common.all;
use work.decode_types.all;
use work.insn_helpers.all;
entity predecoder is
generic (
HAS_FPU : boolean := true;
WIDTH : natural := 2;
ICODE_LEN : natural := 10;
IMAGE_LEN : natural := 26
);
port (
clk : in std_ulogic;
valid_in : in std_ulogic;
insns_in : in std_ulogic_vector(WIDTH * 32 - 1 downto 0);
icodes_out : out std_ulogic_vector(WIDTH * (ICODE_LEN + IMAGE_LEN) - 1 downto 0)
);
end entity predecoder;
architecture behaviour of predecoder is
type predecoder_rom_t is array(0 to 2047) of insn_code;
constant major_predecode_rom : predecoder_rom_t := (
2#001100_00000# to 2#001100_11111# => INSN_addic,
2#001101_00000# to 2#001101_11111# => INSN_addic_dot,
2#001110_00000# to 2#001110_11111# => INSN_addi,
2#001111_00000# to 2#001111_11111# => INSN_addis,
2#010011_00100# to 2#010011_00101# => INSN_addpcis,
2#011100_00000# to 2#011100_11111# => INSN_andi_dot,
2#011101_00000# to 2#011101_11111# => INSN_andis_dot,
2#000000_00000# => INSN_attn,
2#010010_00000# to 2#010010_11111# => INSN_b,
2#010000_00000# to 2#010000_11111# => INSN_bc,
2#001011_00000# to 2#001011_11111# => INSN_cmpi,
2#001010_00000# to 2#001010_11111# => INSN_cmpli,
2#100010_00000# to 2#100010_11111# => INSN_lbz,
2#100011_00000# to 2#100011_11111# => INSN_lbzu,
2#110010_00000# to 2#110010_11111# => INSN_lfd,
2#110011_00000# to 2#110011_11111# => INSN_lfdu,
2#110000_00000# to 2#110000_11111# => INSN_lfs,
2#110001_00000# to 2#110001_11111# => INSN_lfsu,
2#101010_00000# to 2#101010_11111# => INSN_lha,
2#101011_00000# to 2#101011_11111# => INSN_lhau,
2#101000_00000# to 2#101000_11111# => INSN_lhz,
2#101001_00000# to 2#101001_11111# => INSN_lhzu,
2#100000_00000# to 2#100000_11111# => INSN_lwz,
2#100001_00000# to 2#100001_11111# => INSN_lwzu,
2#000111_00000# to 2#000111_11111# => INSN_mulli,
2#011000_00000# to 2#011000_11111# => INSN_ori,
2#011001_00000# to 2#011001_11111# => INSN_oris,
2#010100_00000# to 2#010100_11111# => INSN_rlwimi,
2#010101_00000# to 2#010101_11111# => INSN_rlwinm,
2#010111_00000# to 2#010111_11111# => INSN_rlwnm,
2#010001_00000# to 2#010001_11111# => INSN_sc,
2#100110_00000# to 2#100110_11111# => INSN_stb,
2#100111_00000# to 2#100111_11111# => INSN_stbu,
2#110110_00000# to 2#110110_11111# => INSN_stfd,
2#110111_00000# to 2#110111_11111# => INSN_stfdu,
2#110100_00000# to 2#110100_11111# => INSN_stfs,
2#110101_00000# to 2#110101_11111# => INSN_stfsu,
2#101100_00000# to 2#101100_11111# => INSN_sth,
2#101101_00000# to 2#101101_11111# => INSN_sthu,
2#100100_00000# to 2#100100_11111# => INSN_stw,
2#100101_00000# to 2#100101_11111# => INSN_stwu,
2#001000_00000# to 2#001000_11111# => INSN_subfic,
2#000010_00000# to 2#000010_11111# => INSN_tdi,
2#000011_00000# to 2#000011_11111# => INSN_twi,
2#011010_00000# to 2#011010_11111# => INSN_xori,
2#011011_00000# to 2#011011_11111# => INSN_xoris,
-- major opcode 4
2#000100_10000# => INSN_maddhd,
2#000100_10001# => INSN_maddhdu,
2#000100_10011# => INSN_maddld,
-- major opcode 30
2#011110_01000# to 2#011110_01001# => INSN_rldic,
2#011110_01010# to 2#011110_01011# => INSN_rldic,
2#011110_00000# to 2#011110_00001# => INSN_rldicl,
2#011110_00010# to 2#011110_00011# => INSN_rldicl,
2#011110_00100# to 2#011110_00101# => INSN_rldicr,
2#011110_00110# to 2#011110_00111# => INSN_rldicr,
2#011110_01100# to 2#011110_01101# => INSN_rldimi,
2#011110_01110# to 2#011110_01111# => INSN_rldimi,
2#011110_10000# to 2#011110_10001# => INSN_rldcl,
2#011110_10010# to 2#011110_10011# => INSN_rldcr,
-- major opcode 58
2#111010_00000# => INSN_ld,
2#111010_00001# => INSN_ldu,
2#111010_00010# => INSN_lwa,
2#111010_00100# => INSN_ld,
2#111010_00101# => INSN_ldu,
2#111010_00110# => INSN_lwa,
2#111010_01000# => INSN_ld,
2#111010_01001# => INSN_ldu,
2#111010_01010# => INSN_lwa,
2#111010_01100# => INSN_ld,
2#111010_01101# => INSN_ldu,
2#111010_01110# => INSN_lwa,
2#111010_10000# => INSN_ld,
2#111010_10001# => INSN_ldu,
2#111010_10010# => INSN_lwa,
2#111010_10100# => INSN_ld,
2#111010_10101# => INSN_ldu,
2#111010_10110# => INSN_lwa,
2#111010_11000# => INSN_ld,
2#111010_11001# => INSN_ldu,
2#111010_11010# => INSN_lwa,
2#111010_11100# => INSN_ld,
2#111010_11101# => INSN_ldu,
2#111010_11110# => INSN_lwa,
-- major opcode 59
2#111011_00100# to 2#111011_00101# => INSN_fdivs,
2#111011_01000# to 2#111011_01001# => INSN_fsubs,
2#111011_01010# to 2#111011_01011# => INSN_fadds,
2#111011_01100# to 2#111011_01101# => INSN_fsqrts,
2#111011_10000# to 2#111011_10001# => INSN_fres,
2#111011_10010# to 2#111011_10011# => INSN_fmuls,
2#111011_10100# to 2#111011_10101# => INSN_frsqrtes,
2#111011_11000# to 2#111011_11001# => INSN_fmsubs,
2#111011_11010# to 2#111011_11011# => INSN_fmadds,
2#111011_11100# to 2#111011_11101# => INSN_fnmsubs,
2#111011_11110# to 2#111011_11111# => INSN_fnmadds,
-- major opcode 62
2#111110_00000# => INSN_std,
2#111110_00001# => INSN_stdu,
2#111110_00100# => INSN_std,
2#111110_00101# => INSN_stdu,
2#111110_01000# => INSN_std,
2#111110_01001# => INSN_stdu,
2#111110_01100# => INSN_std,
2#111110_01101# => INSN_stdu,
2#111110_10000# => INSN_std,
2#111110_10001# => INSN_stdu,
2#111110_10100# => INSN_std,
2#111110_10101# => INSN_stdu,
2#111110_11000# => INSN_std,
2#111110_11001# => INSN_stdu,
2#111110_11100# => INSN_std,
2#111110_11101# => INSN_stdu,
-- major opcode 63
2#111111_00100# to 2#111111_00101# => INSN_fdiv,
2#111111_01000# to 2#111111_01001# => INSN_fsub,
2#111111_01010# to 2#111111_01011# => INSN_fadd,
2#111111_01100# to 2#111111_01101# => INSN_fsqrt,
2#111111_01110# to 2#111111_01111# => INSN_fsel,
2#111111_10000# to 2#111111_10001# => INSN_fre,
2#111111_10010# to 2#111111_10011# => INSN_fmul,
2#111111_10100# to 2#111111_10101# => INSN_frsqrte,
2#111111_11000# to 2#111111_11001# => INSN_fmsub,
2#111111_11010# to 2#111111_11011# => INSN_fmadd,
2#111111_11100# to 2#111111_11101# => INSN_fnmsub,
2#111111_11110# to 2#111111_11111# => INSN_fnmadd,
Decode prefixed instructions This adds logic to do basic decoding of the prefixed instructions defined in PowerISA v3.1B which are in the SFFS (Scalar Fixed plus Floating-Point Subset) compliancy subset. In PowerISA v3.1B SFFS, there are 14 prefixed load/store instructions plus the prefixed no-op instruction (pnop). The prefixed load/store instructions all use an extended version of D-form, which has an extra 18 bits of displacement in the prefix, plus an 'R' bit which enables PC-relative addressing. When decode1 sees an instruction word where the insn_code is INSN_prefix (i.e. the primary opcode was 1), it stores the prefix word and sends nothing down to decode2 in that cycle. When the next valid instruction word arrives, it is interpreted as a suffix, meaning that its insn_code gets modified before being used to look up the decode table. The insn_code values are rearranged so that the values for instructions which are the suffix of a valid prefixed instruction are all at even indexes, and the corresponding prefixed instructions follow immediately, so that an insn_code value can be converted to the corresponding prefixed value by setting the LSB of the insn_code value. There are two prefixed instructions, pld and pstd, for which the suffix is not a valid SFFS instruction by itself, so these have been given dummy insn_code values which decode as illegal (INSN_op57 and INSN_op61). For a prefixed instruction, decode1 examines the type and subtype fields of the prefix and checks that the suffix is valid for the type and subtype. This check doesn't affect which entry of the decode table is used; the result is passed down to decode2, and will in future be acted upon in execute1. The instruction address passed down to decode2 is the address of the prefix. To enable this, part of the instruction address is saved when the prefix is seen, and then the instruction address received from icache is partly overlaid by the saved prefix address. Because prefixed instructions are not permitted to cross 64-byte boundaries, we only need to save bits 5:2 of the instruction to do this. If the alignment restriction ever gets relaxed, we will then need to save more bits of the address. Decode2 has been extended to handle the R bit of the prefix (in 8LS and MLS forms) and to be able to generate the 34-bit immediate value from the prefix and suffix. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
1 year ago
-- prefix word, PO1
2#000001_00000# to 2#000001_11111# => INSN_prefix,
-- Major opcodes 57 and 61 are SFFS load/store instructions when prefixed
2#111001_00000# to 2#111001_11111# => INSN_op57,
2#111101_00000# to 2#111101_11111# => INSN_op61,
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
others => INSN_illegal
);
constant row_predecode_rom : predecoder_rom_t := (
-- Major opcode 31
-- Address bits are 0, insn(10:1)
2#0_01000_01010# => INSN_add,
2#0_11000_01010# => INSN_add, -- addo
2#0_00000_01010# => INSN_addc,
2#0_10000_01010# => INSN_addc, -- addco
2#0_00100_01010# => INSN_adde,
2#0_10100_01010# => INSN_adde, -- addeo
2#0_00101_01010# => INSN_addex,
2#0_00010_01010# => INSN_addg6s,
2#0_00111_01010# => INSN_addme,
2#0_10111_01010# => INSN_addme, -- addmeo
2#0_00110_01010# => INSN_addze,
2#0_10110_01010# => INSN_addze, -- addzeo
2#0_00000_11100# => INSN_and,
2#0_00001_11100# => INSN_andc,
2#0_00111_11100# => INSN_bperm,
2#0_01001_11010# => INSN_cbcdtd,
2#0_01000_11010# => INSN_cdtbcd,
2#0_00000_00000# => INSN_cmp,
2#0_01111_11100# => INSN_cmpb,
2#0_00111_00000# => INSN_cmpeqb,
2#0_00001_00000# => INSN_cmpl,
2#0_00110_00000# => INSN_cmprb,
2#0_00001_11010# => INSN_cntlzd,
2#0_00000_11010# => INSN_cntlzw,
2#0_10001_11010# => INSN_cnttzd,
2#0_10000_11010# => INSN_cnttzw,
2#0_10111_10011# => INSN_darn,
2#0_00010_10110# => INSN_dcbf,
2#0_00001_10110# => INSN_dcbst,
2#0_01000_10110# => INSN_dcbt,
2#0_00111_10110# => INSN_dcbtst,
2#0_11111_10110# => INSN_dcbz,
2#0_01100_01001# => INSN_divdeu,
2#0_11100_01001# => INSN_divdeu, -- divdeuo
2#0_01100_01011# => INSN_divweu,
2#0_11100_01011# => INSN_divweu, -- divweuo
2#0_01101_01001# => INSN_divde,
2#0_11101_01001# => INSN_divde, -- divdeo
2#0_01101_01011# => INSN_divwe,
2#0_11101_01011# => INSN_divwe, -- divweo
2#0_01110_01001# => INSN_divdu,
2#0_11110_01001# => INSN_divdu, -- divduo
2#0_01110_01011# => INSN_divwu,
2#0_11110_01011# => INSN_divwu, -- divwuo
2#0_01111_01001# => INSN_divd,
2#0_11111_01001# => INSN_divd, -- divdo
2#0_01111_01011# => INSN_divw,
2#0_11111_01011# => INSN_divw, -- divwo
2#0_11001_10110# => INSN_nop, -- dss
2#0_01010_10110# => INSN_nop, -- dst
2#0_01011_10110# => INSN_nop, -- dstst
2#0_11010_10110# => INSN_eieio,
2#0_01000_11100# => INSN_eqv,
2#0_11101_11010# => INSN_extsb,
2#0_11100_11010# => INSN_extsh,
2#0_11110_11010# => INSN_extsw,
2#0_11011_11010# => INSN_extswsli,
2#0_11011_11011# => INSN_extswsli,
2#0_11110_10110# => INSN_icbi,
2#0_00000_10110# => INSN_icbt,
2#0_00000_01111# => INSN_isel,
2#0_00001_01111# => INSN_isel,
2#0_00010_01111# => INSN_isel,
2#0_00011_01111# => INSN_isel,
2#0_00100_01111# => INSN_isel,
2#0_00101_01111# => INSN_isel,
2#0_00110_01111# => INSN_isel,
2#0_00111_01111# => INSN_isel,
2#0_01000_01111# => INSN_isel,
2#0_01001_01111# => INSN_isel,
2#0_01010_01111# => INSN_isel,
2#0_01011_01111# => INSN_isel,
2#0_01100_01111# => INSN_isel,
2#0_01101_01111# => INSN_isel,
2#0_01110_01111# => INSN_isel,
2#0_01111_01111# => INSN_isel,
2#0_10000_01111# => INSN_isel,
2#0_10001_01111# => INSN_isel,
2#0_10010_01111# => INSN_isel,
2#0_10011_01111# => INSN_isel,
2#0_10100_01111# => INSN_isel,
2#0_10101_01111# => INSN_isel,
2#0_10110_01111# => INSN_isel,
2#0_10111_01111# => INSN_isel,
2#0_11000_01111# => INSN_isel,
2#0_11001_01111# => INSN_isel,
2#0_11010_01111# => INSN_isel,
2#0_11011_01111# => INSN_isel,
2#0_11100_01111# => INSN_isel,
2#0_11101_01111# => INSN_isel,
2#0_11110_01111# => INSN_isel,
2#0_11111_01111# => INSN_isel,
2#0_00001_10100# => INSN_lbarx,
2#0_11010_10101# => INSN_lbzcix,
2#0_00011_10111# => INSN_lbzux,
2#0_00010_10111# => INSN_lbzx,
2#0_00010_10100# => INSN_ldarx,
2#0_10000_10100# => INSN_ldbrx,
2#0_11011_10101# => INSN_ldcix,
2#0_00001_10101# => INSN_ldux,
2#0_00000_10101# => INSN_ldx,
2#0_10010_10111# => INSN_lfdx,
2#0_10011_10111# => INSN_lfdux,
2#0_11010_10111# => INSN_lfiwax,
2#0_11011_10111# => INSN_lfiwzx,
2#0_10000_10111# => INSN_lfsx,
2#0_10001_10111# => INSN_lfsux,
2#0_00011_10100# => INSN_lharx,
2#0_01011_10111# => INSN_lhaux,
2#0_01010_10111# => INSN_lhax,
2#0_11000_10110# => INSN_lhbrx,
2#0_11001_10101# => INSN_lhzcix,
2#0_01001_10111# => INSN_lhzux,
2#0_01000_10111# => INSN_lhzx,
2#0_00000_10100# => INSN_lwarx,
2#0_01011_10101# => INSN_lwaux,
2#0_01010_10101# => INSN_lwax,
2#0_10000_10110# => INSN_lwbrx,
2#0_11000_10101# => INSN_lwzcix,
2#0_00001_10111# => INSN_lwzux,
2#0_00000_10111# => INSN_lwzx,
2#0_10010_00000# => INSN_mcrxrx,
2#0_00000_10011# => INSN_mfcr,
2#0_00010_10011# => INSN_mfmsr,
2#0_01010_10011# => INSN_mfspr,
2#0_01000_01001# => INSN_modud,
2#0_01000_01011# => INSN_moduw,
2#0_11000_01001# => INSN_modsd,
2#0_11000_01011# => INSN_modsw,
2#0_00100_10000# => INSN_mtcrf,
2#0_00100_10010# => INSN_mtmsr,
2#0_00101_10010# => INSN_mtmsrd,
2#0_01110_10011# => INSN_mtspr,
2#0_00010_01001# => INSN_mulhd,
2#0_00000_01001# => INSN_mulhdu,
2#0_00010_01011# => INSN_mulhw,
2#0_00000_01011# => INSN_mulhwu,
-- next 4 have reserved bit set
2#0_10010_01001# => INSN_mulhd,
2#0_10000_01001# => INSN_mulhdu,
2#0_10010_01011# => INSN_mulhw,
2#0_10000_01011# => INSN_mulhwu,
2#0_00111_01001# => INSN_mulld,
2#0_10111_01001# => INSN_mulld, -- mulldo
2#0_00111_01011# => INSN_mullw,
2#0_10111_01011# => INSN_mullw, -- mullwo
2#0_01110_11100# => INSN_nand,
2#0_00011_01000# => INSN_neg,
2#0_10011_01000# => INSN_neg, -- nego
-- next 8 are reserved no-op instructions
2#0_10000_10010# => INSN_nop,
2#0_10001_10010# => INSN_nop,
2#0_10010_10010# => INSN_nop,
2#0_10011_10010# => INSN_nop,
2#0_10100_10010# => INSN_nop,
2#0_10101_10010# => INSN_nop,
2#0_10110_10010# => INSN_nop,
2#0_10111_10010# => INSN_nop,
2#0_00011_11100# => INSN_nor,
2#0_01101_11100# => INSN_or,
2#0_01100_11100# => INSN_orc,
2#0_00011_11010# => INSN_popcntb,
2#0_01111_11010# => INSN_popcntd,
2#0_01011_11010# => INSN_popcntw,
2#0_00101_11010# => INSN_prtyd,
2#0_00100_11010# => INSN_prtyw,
2#0_00100_00000# => INSN_setb,
Implement set[n]bc[r] instructions This implements the setbc, setnbc, setbcr and setnbcr instructions. Because the insn_type_t type already has 64 elements, this uses the existing OP_SETB for the new instructions, and has execute1 compute different results depending on bits 6-9 of the instruction. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
1 year ago
2#0_01100_00000# => INSN_setb, -- setbc
2#0_01101_00000# => INSN_setb, -- setbcr
2#0_01110_00000# => INSN_setb, -- setnbc
2#0_01111_00000# => INSN_setb, -- setnbcr
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
2#0_01111_10010# => INSN_slbia,
2#0_00000_11011# => INSN_sld,
2#0_00000_11000# => INSN_slw,
2#0_11000_11010# => INSN_srad,
2#0_11001_11010# => INSN_sradi,
2#0_11001_11011# => INSN_sradi,
2#0_11000_11000# => INSN_sraw,
2#0_11001_11000# => INSN_srawi,
2#0_10000_11011# => INSN_srd,
2#0_10000_11000# => INSN_srw,
2#0_11110_10101# => INSN_stbcix,
2#0_10101_10110# => INSN_stbcx,
2#0_00111_10111# => INSN_stbux,
2#0_00110_10111# => INSN_stbx,
2#0_10100_10100# => INSN_stdbrx,
2#0_11111_10101# => INSN_stdcix,
2#0_00110_10110# => INSN_stdcx,
2#0_00101_10101# => INSN_stdux,
2#0_00100_10101# => INSN_stdx,
2#0_10110_10111# => INSN_stfdx,
2#0_10111_10111# => INSN_stfdux,
2#0_11110_10111# => INSN_stfiwx,
2#0_10100_10111# => INSN_stfsx,
2#0_10101_10111# => INSN_stfsux,
2#0_11100_10110# => INSN_sthbrx,
2#0_11101_10101# => INSN_sthcix,
2#0_10110_10110# => INSN_sthcx,
2#0_01101_10111# => INSN_sthux,
2#0_01100_10111# => INSN_sthx,
2#0_10100_10110# => INSN_stwbrx,
2#0_11100_10101# => INSN_stwcix,
2#0_00100_10110# => INSN_stwcx,
2#0_00101_10111# => INSN_stwux,
2#0_00100_10111# => INSN_stwx,
2#0_00001_01000# => INSN_subf,
2#0_10001_01000# => INSN_subf, -- subfo
2#0_00000_01000# => INSN_subfc,
2#0_10000_01000# => INSN_subfc, -- subfco
2#0_00100_01000# => INSN_subfe,
2#0_10100_01000# => INSN_subfe, -- subfeo
2#0_00111_01000# => INSN_subfme,
2#0_10111_01000# => INSN_subfme, -- subfmeo
2#0_00110_01000# => INSN_subfze,
2#0_10110_01000# => INSN_subfze, -- subfzeo
2#0_10010_10110# => INSN_sync,
2#0_00010_00100# => INSN_td,
2#0_00000_00100# => INSN_tw,
2#0_01001_10010# => INSN_tlbie,
2#0_01000_10010# => INSN_tlbiel,
2#0_10001_10110# => INSN_tlbsync,
2#0_00000_11110# => INSN_wait,
2#0_01001_11100# => INSN_xor,
-- Major opcode 19
-- Columns with insn(4) = '1' are all illegal and not mapped here; to
-- fit into 2048 entries, the columns are remapped so that 16-24 are
-- stored here as 8-15; in other words the address bits are
-- 1, insn(10..6), 1, insn(5), insn(3..1)
predecode: Add more comments to row_predecode_rom and insn_code values This adds comments to row_predecode_rom to aid understanding how the columns in the second half of the table are allocated to different primary opcodes, and to the insn_code values to assist in locating the code with a given numeric value. No code change. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
-- Columns 16-17 here are opcode 19 columns 0-1
-- Columns 24-31 here are opcode 19 columns 16-23
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
2#1_10000_11000# => INSN_bcctr,
2#1_00000_11000# => INSN_bclr,
2#1_10001_11000# => INSN_bctar,
2#1_01000_10001# => INSN_crand,
2#1_00100_10001# => INSN_crandc,
2#1_01001_10001# => INSN_creqv,
2#1_00111_10001# => INSN_crnand,
2#1_00001_10001# => INSN_crnor,
2#1_01110_10001# => INSN_cror,
2#1_01101_10001# => INSN_crorc,
2#1_00110_10001# => INSN_crxor,
2#1_00100_11110# => INSN_isync,
2#1_00000_10000# => INSN_mcrf,
2#1_00000_11010# => INSN_rfid,
-- Major opcode 59
predecode: Add more comments to row_predecode_rom and insn_code values This adds comments to row_predecode_rom to aid understanding how the columns in the second half of the table are allocated to different primary opcodes, and to the insn_code values to assist in locating the code with a given numeric value. No code change. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
-- Address bits are 1, insn(10..6), 1, 0, insn(3..1)
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
-- Only column 14 is valid here; columns 16-31 are handled in the major table
predecode: Add more comments to row_predecode_rom and insn_code values This adds comments to row_predecode_rom to aid understanding how the columns in the second half of the table are allocated to different primary opcodes, and to the insn_code values to assist in locating the code with a given numeric value. No code change. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
-- Column 14 is mapped to column 22.
-- Columns 20-23 here are opcode 59 columns 12-15
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
2#1_11010_10110# => INSN_fcfids,
2#1_11110_10110# => INSN_fcfidus,
-- Major opcode 63
-- Columns 0-15 are mapped here; columns 16-31 are in the major table.
-- Address bits are 1, insn(10:6), 0, insn(4:1)
predecode: Add more comments to row_predecode_rom and insn_code values This adds comments to row_predecode_rom to aid understanding how the columns in the second half of the table are allocated to different primary opcodes, and to the insn_code values to assist in locating the code with a given numeric value. No code change. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
-- Columns 0-15 here are opcode 63 columns 0-15
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
2#1_00000_00000# => INSN_fcmpu,
2#1_00001_00000# => INSN_fcmpo,
2#1_00010_00000# => INSN_mcrfs,
2#1_00100_00000# => INSN_ftdiv,
2#1_00101_00000# => INSN_ftsqrt,
2#1_00001_00110# => INSN_mtfsb,
2#1_00010_00110# => INSN_mtfsb,
2#1_00100_00110# => INSN_mtfsfi,
2#1_11010_00110# => INSN_fmrgow,
2#1_11110_00110# => INSN_fmrgew,
2#1_10010_00111# => INSN_mffs,
2#1_10110_00111# => INSN_mtfsf,
2#1_00000_01000# => INSN_fcpsgn,
2#1_00001_01000# => INSN_fneg,
2#1_00010_01000# => INSN_fmr,
2#1_00100_01000# => INSN_fnabs,
2#1_01000_01000# => INSN_fabs,
2#1_01100_01000# => INSN_frin,
2#1_01101_01000# => INSN_friz,
2#1_01110_01000# => INSN_frip,
2#1_01111_01000# => INSN_frim,
2#1_00000_01100# => INSN_frsp,
2#1_00000_01110# => INSN_fctiw,
2#1_00100_01110# => INSN_fctiwu,
2#1_11001_01110# => INSN_fctid,
2#1_11010_01110# => INSN_fcfid,
2#1_11101_01110# => INSN_fctidu,
2#1_11110_01110# => INSN_fcfidu,
2#1_00000_01111# => INSN_fctiwz,
2#1_00100_01111# => INSN_fctiwuz,
2#1_11001_01111# => INSN_fctidz,
2#1_11101_01111# => INSN_fctiduz,
others => INSN_illegal
);
constant IOUT_LEN : natural := ICODE_LEN + IMAGE_LEN;
type predec_t is record
image : std_ulogic_vector(31 downto 0);
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
maj_predecode : unsigned(ICODE_LEN - 1 downto 0);
row_predecode : unsigned(ICODE_LEN - 1 downto 0);
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
end record;
subtype index_t is integer range 0 to WIDTH-1;
type predec_array is array(index_t) of predec_t;
signal pred : predec_array;
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
signal valid : std_ulogic;
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
begin
predecode_0: process(clk)
variable majaddr : std_ulogic_vector(10 downto 0);
variable rowaddr : std_ulogic_vector(10 downto 0);
variable iword : std_ulogic_vector(31 downto 0);
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
variable majcode : insn_code;
variable rowcode : insn_code;
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
begin
if rising_edge(clk) then
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
valid <= valid_in;
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
for i in index_t loop
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
iword := insns_in(i * 32 + 31 downto i * 32);
pred(i).image <= iword;
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
if is_X(iword) then
pred(i).maj_predecode <= (others => 'X');
pred(i).row_predecode <= (others => 'X');
else
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
majaddr := iword(31 downto 26) & iword(4 downto 0);
-- row_predecode_rom is used for op 19, 31, 59, 63
-- addr bit 10 is 0 for op 31, 1 for 19, 59, 63
rowaddr(10) := iword(31) or not iword(29);
rowaddr(9 downto 5) := iword(10 downto 6);
if iword(28) = '0' then
-- op 19 and op 59
rowaddr(4 downto 3) := '1' & iword(5);
else
-- op 31 and 63; for 63 we only use this when iword(5) = '0'
rowaddr(4 downto 3) := iword(5 downto 4);
end if;
rowaddr(2 downto 0) := iword(3 downto 1);
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
majcode := major_predecode_rom(to_integer(unsigned(majaddr)));
pred(i).maj_predecode <= to_unsigned(insn_code'pos(majcode), ICODE_LEN);
rowcode := row_predecode_rom(to_integer(unsigned(rowaddr)));
pred(i).row_predecode <= to_unsigned(insn_code'pos(rowcode), ICODE_LEN);
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
end if;
end loop;
end if;
end process;
predecode_1: process(all)
variable iword : std_ulogic_vector(31 downto 0);
variable use_row : std_ulogic;
variable illegal : std_ulogic;
variable ici : std_ulogic_vector(IOUT_LEN - 1 downto 0);
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
variable icode : unsigned(ICODE_LEN - 1 downto 0);
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
begin
for i in index_t loop
iword := pred(i).image;
icode := pred(i).maj_predecode;
use_row := '0';
illegal := '0';
case iword(31 downto 26) is
when "000100" => -- 4
-- major opcode 4, mostly VMX/VSX stuff but also some integer ops (madd*)
illegal := not iword(5);
when "010011" => -- 19
-- Columns 8-15 and 24-31 don't have any valid instructions
-- (where insn(5..1) is the column number).
-- addpcis (column 2) is in the major table
-- Other valid columns are mapped to columns in the second
-- half of the row table: columns 0-1 are mapped to 16-17
-- and 16-23 are mapped to 24-31.
illegal := iword(4);
use_row := iword(5) or (not iword(3) and not iword(2));
when "011000" => -- 24
-- ori, special-case the standard NOP
if std_match(iword, "01100000000000000000000000000000") then
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
icode := to_unsigned(insn_code'pos(INSN_nop), ICODE_LEN);
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
end if;
when "011111" => -- 31
-- major opcode 31, lots of things
-- Use the first half of the row table for all columns
use_row := '1';
when "111011" => -- 59
-- floating point operations, mostly single-precision
-- Columns 0-11 are illegal; columns 12-15 are mapped
-- to columns 20-23 in the second half of the row table,
-- and columns 16-31 are in the major table.
illegal := not iword(5) and (not iword(4) or not iword(3));
use_row := not iword(5);
when "111111" => -- 63
-- floating point operations, general and double-precision
-- Use columns 0-15 of the second half of the row table
-- for columns 0-15, and the major table for columns 16-31.
use_row := not iword(5);
when others =>
end case;
if use_row = '1' then
icode := pred(i).row_predecode;
end if;
-- Mark FP instructions as illegal if we don't have an FPU
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
if not HAS_FPU and not is_X(icode) and
to_integer(icode) >= insn_code'pos(INSN_first_frs) then
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
illegal := '1';
end if;
ici(31 downto 0) := iword;
ici(IOUT_LEN - 1 downto 32) := (others => '0');
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
if valid = '0' or illegal = '1' or is_X(icode) or
icode = to_unsigned(insn_code'pos(INSN_illegal), ICODE_LEN) then
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
-- Since an insn_code currently fits in 9 bits, use just
-- the most significant bit of ici to indicate illegal insns.
ici(IOUT_LEN - 1) := '1';
else
predecode: Work around apparent yosys/nextpnr bug This rearranges the synchronous process here to avoid setting fields of pred(i) to zero or INSN_illegal when valid_in is '0'. Experimentally, on ECP5 this acts like an asynchronous reset rather than a synchronous reset. Instead, handle possible indeterminate input for simulation by making the maj_predecode and row_predecode fields of predec_t be unsigned rather than insn_code (an enumerated type), and setting them to X when the input word is indeterminate. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
ici(IOUT_LEN - 1 downto IMAGE_LEN) := std_ulogic_vector(icode);
Pre-decode instructions when writing them to icache This splits out the decoding done in the decode0 step into a separate predecoder, used when writing instructions into the icache. The icache now holds 36 bits per instruction rather than 32. For valid instructions, those 36 bits comprise the bottom 26 bits of the instruction word, a 9-bit insn_code value (which uniquely identifies the instruction), and a zero in the MSB. For illegal instructions, the MSB is one and the full instruction word is in the bottom 32 bits. Having the full instruction word available for illegal instructions means that it can be printed in the log when simulating, or in future could be placed in the HEIR register. If we don't have an FPU, then the floating-point instructions are regarded as illegal. In that case, the insn_code values would fit into 8 bits, which could be used in future to reduce the size of decode_rom from 512 to 256 entries. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
end if;
icodes_out(i * IOUT_LEN + IOUT_LEN - 1 downto i * IOUT_LEN) <= ici;
end loop;
end process;
end architecture behaviour;