feat(Backend, MemBlock): add support for Zacas extension #3958
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misc: remove assert temporarily
fix(AtomicsUnit, MemBlock): fix loss of multiple stds In the previous design, AtomicsUnit receives stds from StdExeUnit and arbitrate at most one std uop for one cycle. This works fine on most of the AMOs and LR/SC because they require only one std uop. However AMOCAS requires at least two std uops, which may be issued from two separate issue queues at the same time, leading to the loss of std uops. This commit fixes this by taking all the outputs of the StdExeUnits into account with arbitration logics. fix(AtomicsUnit): DCache req can only be sent at `s_cache_req` fix(AtomicsUnit, difftest): fix difftest io for atomic events fix(MainPipe): fix precedence of `&` and `=/=` operator fix(MainPipe): AMOCAS should not wait for AMOALU fix(MemBlock): remove unnecessary assertion fix(MainPipe): only CAS instruction can assert `s3_cas_fail` fix(AtomicsUnit): fix bug in data select logic submodule(difftest): bump difftest
* spike commit: 9ab4cebc0caf121695b77f78ca6d2481fe9b182f
* spike config: CPU=XIANGSHAN
Including:
* feat(Zacas): enable Zacas entension.
* NEMU commit: bf877e0b34092517c909afc9c58ebc803dd8cf3f
* NEMU configs:
* riscv64-xs-ref_defconfig
* riscv64-dual-xs-ref_defconfig
Including:
* config(Zacas): enable Zacas entension.
* submodule(ready-to-run): Bump spike ref in ready-to-run
* ci: add ci tests for Zacas extension.
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This pull request implements Zacas extension for atomic Compare-and-Swap (CAS) instructions. For RV64, AMOCAS.W / AMOCAS.D / AMOCAS.Q atomically loads 32 / 64 / 128-bits of a data value from rs1, compares the loaded value to register rd (for AMOCAS.Q, a register pair consisting of rd and rd+1), and if the comparison is bitwise equal, then stores the value held in rs2 (for AMOCAS.Q, a register pair consisting of rs2 and rs2+1) to the original address in rs1.
This pull request re-uses the existing AtomicsUnit design. However, an AMOCAS instruction may consume more than 1 std and even more than 1 sta in the new design. As far as stds,
As for stas, AMOCAS.Q has extra require for the number of sta uops, which is also the number of sta uops' write-back,
Besides, this pr removes the write-back of atomic stds.