Commit Graph

270 Commits (bdc26b7527c3fa66de099473df07e6bb0272333e)
 

Author SHA1 Message Date
Paul Mackerras 7fe84220a5 decode: Avoid multiplexing from instruction reg fields to regfile address ports
This aims to simplify the logic between the instruction image and
the register file read address ports and reduce the size of the decode
tables.  With this patch, the input_reg_a column of the decode tables
can only select RA or zeroes, the input_reg_b column can only select
RB or a constant (0, -1, or an immediate value from the instruction),
and the input_reg_c columns can only select RS or zeroes.

That means that the rotate/shift/logical ops now have their first
input coming in via the input_reg_c column.  That means we need to
add a read_data3 field to the Decode2ToExecuteType record, but that
will go away again when we split out the rotate/mask/logical ops to
their own unit.

As a related but not tightly connected change, this patch also sets
the read1_enable signal to the register file be 0 when RA=0 and the
input_reg_a for the instruction is RA_OR_ZERO (previously it was 1).

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras 96b402a4bf Consolidate add/subtract instructions into a single op
All of the PPC add and subtract instructions, including carrying
and extended versions, do much the same arithmetic operation:

	result = (I xor A) + B + C

where A is the value from RA, I provides a logical inversion of A
(i.e. I is 0 or -1), B is either from RB or is a constant 0 or -1,
and C is 0, 1 or the carry bit from XER (CA).

To consolidate all the add/subtract instructions into a single
OP_ADD, we add a column to decode_rom_t to indicate when A should
be inverted, and change the input_carry field to a 3-state selector
to select C in the equation above.

This also adds a new "CONST_M1" value for input_reg_b_t to indicate
that B is a constant -1.  This allows us to implement addme and
subfme.

The addex instruction appears not to exist, so the comments referring
to it are removed.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Anton Blanchard f1ac8894b1
Merge pull request #80 from antonblanchard/misc
Reduce register file footprint
5 years ago
Paul Mackerras b0f302ecf4 decode: Make all update-form indexed loads and stores use RA_OR_ZERO
Experimentation on POWER9 indicates that the invalid form of lbzux
with RA=0 uses just RB as the address, not R0 + RB.  Extrapolating
this to all update-form loads and stores with RA=0, change all the
update-form loads and stores to use RA_OR_ZERO rather than RA.

This then means that all decode ROM entries with insn_type = LDST
have input_reg_a = RA_OR_ZERO.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Benjamin Herrenschmidt ec1868f7d2 register_file: Move GPRs into distributed RAM
The register file is currently implemented as a whole pile of individual
1-bit registers instead of LUT memory which is a huge waste of FPGA
space.

This is caused by the output signal exposing the register file to the
outside world for simulation debug.

This removes that output, and moves the dumping of the register file
to the register file module itself. This saves about 8% of fpga on
the little Arty A7-35T.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Paul Mackerras 58b06eb5f3 decode: Remove const fields from decode_rom_t
The const* fields of decode_rom_t drove multiplexers in decode2 that
picked out various instruction fields and put them into the const*
fields of the Decode2ToExecute1Type record, from where they were
used in execute1.  However, the code in execute1 can just as easily
use the appropriate fields of the original instruction word, since
that is now available in execute1.  This therefore changes the
code to do that, resulting in smaller decode tables.

Suggested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Benjamin Herrenschmidt a2969fa298 debug/sim: Make connect/disconnect messages quieter
Those don't need to go to stderr, send them to stdout instead

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Paul Mackerras 143d0ae9e4 decode: Fix larx/stcx instructions to use RA_OR_ZERO not RA
The l?arx and st?cx. instructions are defined to use the normal indexed
mode address calculations, i.e. (RA|0) + RB.  Fix their entries in the
decode table to say RA_OR_ZERO rather than RA.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras bbae2d1eda decode: Index minor op table with insn bits for opcode 31
This changes decode_op_31_array from being indexed by a ppc_insn_t
(which is derived from the instruction word by a whole series of
if/elsif statements) to being indexed directly by bits 10...1 of
the instruction word.  With this we no longer need ppc_insn.

This then means that the decode1 stage doesn't distinguish between
mfcr and mfocrf, or between mtcrf and mtocrf, since those are
distinguished by the value in bit 20 of the instruction.  To
accommodate that, execute1 changes so that the one op value (OP_MFCR)
does either the mfcr or the mfocrf behaviour depending on bit 20
of the instruction word; and similarly for mtcrf/mtocrf.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras 21d3f8a5ed decode: Index minor op table with insn bits for opcode 30
This comprises the 64-bit rotate and mask instructions.  In order to
reduce the table index to 3 bits, we combine rldcl and rdlcr into a
single op (OP_RLDCX), and choose the right mask at execute time based
on bit 1 of the instruction word.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras 00e9f801f6 decode: Index minor op table with insn bits for opcode 19
This changes the decoding of major opcode 19 from using the ppc_insn_t
index to using bits of the instruction word directly.  Opcode 19 has
a 10-bit minor opcode field (bits 10..1) but the space is sparsely
filled.  Therefore we index a table of single-bit entries with the
10-bit minor opcode to filter out the illegal minor opcodes, and
index a table using just 3 bits -- 5, 3 and 2 -- of the instruction
to get the decode entry.  This groups together all the instructions
in 4 columns of the opcode map as a single entry.  That means that
mcrf and all the CR logical ops get grouped together, and bcctr, bclr
and bctar get grouped together.  At present the CR logical ops are not
implemented, so their grouping has no impact.

The code for bclr and bcctr in execute1 is now common, using a single
op, and it now determines the branch address by looking at bit 10 of
the instruction word at execute time.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras e30a87593a decode: Start moving towards decoding by major opcode first
With this, we have a table for most major opcodes and separate
tables for each major opcode that has further decoding required.
These tables are still mostly indexed by the ppc_insn_t values,
however.

A few things are still decoded completely at the top level: nop,
attn and sim_config.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras c9e92483b8 decode: Push mtspr/mfspr register decoding down into execute1
Instead of doing mfctr, mflr, mftb, mtctr, mtlr as separate ops,
just pass down mfspr and mtspr ops with the spr number and let
execute1 decode which SPR we're addressing.  This will help reduce
the number of instruction bits decode1 needs to look at.

In fact we now pass down the whole instruction from decode2 to
execute1.  We will need more bits of the instruction in future,
and the tools should just optimize away any that we don't end
up using.  Since the 'aa' bit was just a copy of an instruction
bit, we can now remove it from the record.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Benjamin Herrenschmidt 3e6f656a90 Add MCRF instruction
Hopefully it's not too timing catastrophic. The variable newcrf will
be handy for the other CR ops when we implement them I suspect.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 554ae88540 Implement absolute branches
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Anton Blanchard 4174cd8e93
Merge pull request #77 from antonblanchard/timing
A number of timing fixes
5 years ago
Anton Blanchard 4a9a9df4dd
Merge pull request #76 from antonblanchard/misc
Some misc updates
5 years ago
Benjamin Herrenschmidt 9961d70dfb Improve PLL/MMCM clocks configuration
We can now pass both the input clock and target clock frequency
via generics. Add support for both 50Mhz and 100Mhz target freqs
for both cases.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 5f28109957 Don't reset JTAG request register asynchronously
There's no point and it causes Vivado to spew a pile of warnings

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 48e6e719d3 Multiply needs to be 16 stages to fix all timing issues
This seems dependent on the FPGA type/size, so we should probably
make it a toplevel generic, but for now this helps on the
Arty A7-35

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Paul Mackerras 9789d258fb loadstore2: Do data formatting after a register stage
This moves the data formatting for read data to after a register,
instead of before, in order to improve timing.  The data formatting
is now effectively combinational logic on the input side of the
writeback stage.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Benjamin Herrenschmidt 492bf06740 corefile: Remove duplicate wishbone_debug_master
It's both in core and soc, it should only be in the latter

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt ab5c6ab9ac fpga: Arty A7's don't need multiple filesets
the XDC is identical between variants, so is the fileset

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 80a0e7fcf3 execute1: simplify flush_out
It's always set when f_out.redirect is set, so may as well set it once
at the end. It's all combo from the register.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 8b55fc4d9e Reformat fetch2
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 41a4eb8271 Move fetch2 <-> icache definitions
To a more logical place before decode related ones

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 79b64baefc Remove unused pipe_stop in Fetch1ToFetch2Type
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 79b0b9a046 Fix PLL reset signal name in toplevel
It shouldn't have a _n suffix, it's active positive.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 8af2b004c3 Simplify fetch1
Do the +4 in a single place. This shouldn't cause any difference
in behaviour as these are sequential variable assignments.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 3a6fcc09d4 Reformat fetch1
No code change

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 586abb70a0 Update dependency
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Anton Blanchard feb8ee7149
Merge pull request #75 from paulusmack/master
fpga: Add definitions for Arty A7-100 board
5 years ago
Anton Blanchard 555802d996
Merge pull request #74 from paulusmack/divider
Divider
5 years ago
Paul Mackerras 1158c81500 fpga: Add definitions for Arty A7-100 board
These are a copy of the A7-35 definitions with 35 changed to 100.
The A7-100 uses the same .xdc file (arty_a7-35.xdc) as the A7-35
since the only difference between the two is the FPGA part; the
hardware and connections on the two boards are identical.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras 25b9450475 divider: Do absolute-value ops in divider instead of decode
This moves the negation of negative operands for signed divide and
modulus operations out of the decode2 stage and into the divider.
If either of the operands for a signed divide or modulus operation
is negative, the divider now takes an extra cycle to negate the
operands that are negative.

The interface to the divider now has an 'is_signed' signal rather
than a 'neg_result' signal, and the dividend and divisor can be
negative, so divider_tb had to be updated for the new interface.

The reason for doing this is that one of the worst timing violations
on the Arty A7-100 at 100MHz involved the carry chain in the adders
that did the negation of the dividend and divisor in the decode stage.
Moving the negations to a separate cycle fixes that and also seems to
reduce the total number of slice LUTs used.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Paul Mackerras e6536d4b8b divider: Always compute result/sresult/d_out.write_reg_data
These are intended to be combinatorial.  The previous code was giving
warnings in vivado about registers/latches with no clock defined.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago
Anton Blanchard ad040601e6
Merge pull request #73 from antonblanchard/remove-divide-patch
Remove gcc software divide patch
5 years ago
Anton Blanchard c8328cdf84 Remove gcc software divide patch
We have a divider, thanks to Paul.

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard 82fe8dc6e2
Merge pull request #72 from antonblanchard/build-error
Fix build issue in dmi_dtm_dummy.vhdl
5 years ago
Anton Blanchard a9e5fe78fb
Merge pull request #71 from antonblanchard/dependencies
Update Makefile dependencies
5 years ago
Anton Blanchard 8102e7863b Fix build issue in dmi_dtm_dummy.vhdl
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard 26f70264b3 Update Makefile dependencies
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard b57325ce29 Merge branch 'divider' of https://github.com/paulusmack/microwatt 5 years ago
Anton Blanchard cd4da50650
Merge pull request #70 from antonblanchard/badly-named-carry
Rename OP_SUBFC -> OP_SUBFE, OP_ADDC -> OP_ADDE
5 years ago
Anton Blanchard 5a6f8d26d1 Rename OP_SUBFC -> OP_SUBFE, OP_ADDC -> OP_ADDE
These were somewhat badly named.

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard ba783fddd5
Merge pull request #69 from antonblanchard/debug-module
Merge debug module patches
5 years ago
Anton Blanchard 6cae10eebd Terminate test on illegal instruction
This gets the CI going again, but we will want to fix the test
harness since it's useful to be able to debug the core after it
executes an illegal instruction.

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard 8c5dcc8c4c Fix ghdl error
I'm seeing an issue on my version of ghdl:

  core.vhdl:137:24:error: actual expression must be globally static

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard d82f4c18b6 Add core_debug.vhdl to fusesoc configs
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Paul Mackerras a01ffaeb64 Speed up the divider a little
This looks for cases where the next 8 bits of the quotient are obviously
going to be zero, because the top 72 bits of the 128-bit dividend
register are all zero.  In those cases we shift 8 zero bits into the
quotient and increase count by 8.  We only do this if count < 56.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
5 years ago