This fixes a bug which causes a trace interrupt to store the wrong
value in SRR0 in the case where the instruction that has just
completed is followed by a sc (system call) instruction. What happens
is that first the traced instruction sets ex1.trace_next. Then, when
the sc instruction following it comes in, the execute1_actions process
sets v.e.last_nia to next_nia because it is an sc instruction, even
though it is not going to be executed -- we are going to take the
trace interrupt instead. Then when the trace interrupt is taken, we
incorrectly set SRR0 to the incremented address (the address of the
instruction following the sc).
To fix this, we have execute1_actions set a new flag if the current
instruction is sc, and only set v.e.last_nia to next_nia if we
actually execute the sc (in the "if go = '1'" case).
Fixes: 813e2317bf ("execute1: Restructure to separate out execution of side effects", 2022-06-18)
Reported-by: Anton Blanchard <anton@linux.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Regenerate from upstream litex. Something in the update has improved
memory read and write performance quite a lot on my Nexys Video:
Before:
Write speed: 83.2MiB/s
Read speed: 140.4MiB/s
After:
Write speed: 352.1MiB/s
Read speed: 218.5MiB/s
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
Fix the litex generate script to pass frequencies in Hz. Regenerate
the litesdcard Verilog for both Xilinx and Lattice. This fixes
litesdcard on my Nexys Video.
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
Building the mw_debug program leaves build artifacts in
microwatt/scripts/mw_debug
causing noise in the output of `git status`.
This commit adds them to .gitignore.
Signed-off-by: Boris Shingarov <shingarov@labware.com>
The following commit added two tests but didn't update the tests
outputs:
commit 73cc5167ec
Author: Paul Mackerras <paulus@ozlabs.org>
Date: Mon May 9 19:18:42 2022 +1000
Use FPU for division instructions if we have an FPU
This patch updates these using tests/update_console_tests
Signed-off-by: Michael Neuling <mikey@neuling.org>
This improves timing a little because the register addresses now come
directly from a latch instead of being calculated by
decode_input_reg_*. The asserts that check that the two are the same
are now in decode2 rather than register_file.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
With this, the register RAM is read synchronously using the addresses
supplied by decode1. That means the register RAM can now be block RAM
rather than LUT RAM.
Debug accesses are done via the B port on cycles when decode1
indicates that there is no valid instruction or the instruction
doesn't use a [F]RB operand.
We latch the addresses being read in each cycle and use the same
address next cycle if stalled. Data that is being written is latched
and a multiplexer on each read port then supplies the latched write
data if the read address for that port equals the write address.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This adds some relatively simple logic to decode1 to compute the
GPR/FPR addresses that an instruction will access. It always computes
three addresses regardless of whether the instruction will actually
use all of them. The main things it computes are whether the
instruction uses the RS field or the RC field for the 3rd operand, and
whether the operands are FPRs or GPRs (it is possible for RS to be an
FPR but RA and RB to be GPRs, as for example with stfdx).
At the moment all we do with these computed register addresses is to
assert that they are identical to the ones coming from decode2 one
cycle later.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This eliminates one leg of the output value multiplexer, and seems
to improve timing slightly on the A7-100.
Since SPR values are written in stage 3 and read in stage 2, an mfspr
immediately following an mtspr to the same SPR won't give the correct
value. To avoid this, we make mtspr to the load/store SPRs single
issue in decode1.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This provides access to the SPRs via the JTAG DMI interface. For now
they are still accessed as if they were GPR/FPRs using the same
numbering as before (GPRs at 0 - 0x1f, SPRs at 0x20 - 0x2d, FPRs at
0x40 - 0x5f).
For XER, debug reads now report the full value, not just the bits that
were previously stored in the register file. The "slow" SPR mux is
not used for debug reads.
Decode2 determines on each cycle whether a debug SPR access will
happen next cycle, based on whether there is a request and whether the
current instruction accesses the SPR RAM.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
With this, the register file now contains 64 entries, for 32 GPRs and
32 FPRs, rather than the 128 it had previously. Several things get
simplified - decode1 no longer has to work out the ispr{1,2,o} values,
decode_input_reg_{a,b,c} no longer have the t = SPR case, etc.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
By putting CTR on the odd side and LR and TAR on the even side, we can
read and write CTR for bdnz-style instructions in parallel with
reading LR or TAR for indirect branches and writing LR for branches
with LK=1. Thus we don't need to double up any of these instructions,
giving a simplification in decode2.
We now have logic for printing LR and CTR at the end of a simulation
in execute1, in addition to the similar logic in register_file and
cr_file.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This starts the process of removing SPRs from the register file by
moving SRR0/1, SPRG0-3, HSRR0/1 and HSPRG0/1 out of the register file
and putting them into execute1. They are stored in a pair of small
RAM arrays, referred to as "even" and "odd". The reason for having
two arrays is so that two values can be read and written in each
cycle. For example, SRR0 and SRR1 can be written in parallel by an
interrupt and read in parallel by the rfid instruction.
The addresses in the RAM which will be accessed are determined in the
decode2 stage. We have one write address for both sides, but two read
addresses, since in future we will want to be able to read CTR at the
same time as either LR or TAR.
We now have a connection from writeback to execute1 which carries the
partial SRR1 value for an interrupt. SRR0 comes from the execute
pipeline; we no longer need to carry instruction addresses along the
LSU and FPU pipelines. Since SRR0 and SRR1 can be written in the same
cycle now, we don't need the little state machine in writeback any
more.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
- Arrange for XER to be written for OE=1 forms
- Arrange for condition codes to be set for RC=1 forms
(including correct handling for 32-bit mode)
- Don't instantiate the divider if we have an FPU.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This adds logic to the FPU to accomplish 64-bit integer divisions.
No instruction actually uses this yet.
The algorithm used is to obtain an estimate of the reciprocal of the
divisor using the lookup table and refine it by one to three
iterations of the Newton-Raphson algorithm (the number of iterations
depends on the number of significant bits in the dividend). Then the
reciprocal is multiplied by the dividend to get the quotient estimate.
The remainder is calculated as dividend - quotient * divisor. If the
remainder is greater than or equal to the divisor, the quotient is
incremented, or if a modulo operation is being done, the divisor is
subtracted from the remainder. The inverse estimate after refinement
is good enough that the quotient estimate is always equal to or one
less than the true quotient.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This changes the representation of the R, A, B and C registers in the
FPU from 10.54 format (10 bits to the left of the binary point and 54
bits to the right) to 8.56 format, to match the representation used in
the P and Y registers and the multiplier operands. This eliminates
the need for shifting when R, A, B or C is an input to the multiplier
and will make it easier to implement integer division in the FPU.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This provides a mechanism for tracking updates to the XER overflow
bits (SO, OV, OV32) and stalling instructions which need current
values of those bits (mfxer, integer compare instructions, integer
Rc=1 instructions, addex) or which writes carry bits (since all the
XER common bits are written together, if we are writing CA/CA32 we
need up-to-date values of SO/OV/OV32).
This will enable updates to SO/OV/OV32 to be done at other places
besides the ex1 stage.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This fixes a bug which prevents the core from stopping properly. The
same bug was previously fixed in commit e41cb01bca ("fetch1: Fix
debug stop", 2020-12-19) and reintroduced by commit 0fb207be60
("fetch1: Implement a simple branch target cache", 2020-12-19).
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This lets us get rid of r_int and its 'outstanding' counter. We now
test more directly for excess completions by checking that we don't
get duplicate completions for the same tag.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Now that the timing of the busy signal from decode2 doesn't depend on
register numbers or downstream instruction completion, we no longer
need the stash buffer on the output of decode1.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
At present the busy/stall signal going to decode1 depends on whether
control thinks it can issue the current instruction, and that depends
on completion and bypass signals coming from execute1 and writeback.
To improve the timing of stall_out, this rearranges decode2 so that
stall_out is asserted when we have a valid instruction that couldn't
be issued in the previous cycle. This means that decode1 could give
us a new instruction when we haven't issued the previous instruction.
This in turn means that we can only use d_in in the first cycle of
processing an instruction. After the first cycle, we get register
addresses etc. from dc2 rather than d_in.
Then, to avoid the need to read register operands from register_file
in each cycle until the instruction issues, we bring the bypass path
for data being written to the register file into decode2 explicitly
rather than having it in register_file.
A new process called decode2_addrs does the process of calling
decode_input_reg_* and decode_output_reg and sets up the register file
addresses. This was split out (and decode_input_reg_* reworked) to
try to reduce the number of passes through the decode2_1 process that
need to be done in simulation.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
They are optional in SFFS (scalar fixed-point and floating-point
subset), are not needed for running Linux, and add complexity, so
remove them.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This reduces the set of instructions marked as single-issue to just
attn and mtspr to "slow" SPRs (those that are not stored in the
register file).
The instructions that were previously single-issue are: isync, dcbf,
dcbst, dcbt, dcbtst, eieio, icbi, mfmsr, mtmsr, mtmsrd, mfspr to slow
SPRS, sync, tlbsync and wait. The synchronization instructions are
mostly no-ops anyway due to the in-order nature of the core, and the
cache-management instructions are unimplemented (except for icbi).
The MSR ops don't need to be single-issue due to the in-order core and
the fact that MSR updates are effective on the following instruction.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Anton Blanchard