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[B ISA extension] add carry-less multiply instructions (Zbc) support #260

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merged 9 commits into from
Jan 27, 2022

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@stnolting stnolting commented Jan 26, 2022

This PR is a follow-up of #259 and adds the last missing sub-extension to the CPU's RISC-V bit-manipulation ISA extension "B":

  • Zbc - carry-less multiplication instructions

The NEORV32 CPU now supports all four B subsets (according to the recently frozen and ratified RISC-V bit-manipulation spec. v0.93/v1.00):

  • ✔️ Zbb - basic bit-manipulation instructions
  • ✔️ Zba - address-generation instructions
  • ✔️ Zbs - single-bit instructions
  • ✔️ Zbc - carry-less multiplication instructions

📚 A copy of the RISC-V B spec (v0.93) can be found in docs/references.

Since there is no upstream gcc support yet, Zbc intrinsics and emulation functions have been added to sw/example/bitmanip_test/neorv32_b_extension_intrinsics.h. Furthermore, according test cases have been added to sw/example/bitmanip_test/main.c to verify correct operations.

@stnolting stnolting added enhancement New feature or request risc-v compliance Modification to comply with official RISC-V specs. HW Hardware-related SW Software-related labels Jan 26, 2022
@stnolting stnolting self-assigned this Jan 26, 2022
@stnolting stnolting marked this pull request as ready for review January 27, 2022 04:13
@stnolting stnolting merged commit ce64f6e into master Jan 27, 2022
@stnolting stnolting deleted the b_isa_extension_zbc branch January 27, 2022 09:35
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