# add M extension to big_core

- Source URL: https://github.com/FPGA-MAFIA/fpga_mafia/issues/648

- implement multiplication in HW in straight forward manner.  We do that because FPGA has dedicated multipliers
- implement division as exception trap

PR Title: add m_extension support
Status: Merged
Merged by: amichai-bd on May 21, 2024
Source Branch: big_core_RV32IM → main
Commits: 4

Description:
The contributor successfully implemented RISC-V M extension (multiplication/division) support for the big_core processor. The implementation uses trap-based division handling and includes custom CSR functionality for storing the stack pointer.

Test Command:
./build.py -dut big_core -test m_extension -app -cfg big_core_rv32im -hw -sim

Results demonstrated: Division, unsigned division, remainder, and unsigned remainder operations with test case 34÷4, plus negative number handling and overflow/division-by-zero edge cases.

Key Comments:
roman012285 (Author):
- "it took allot of time to understand the pointers and debug every thing"
- Acknowledged performance concerns with naive division algorithm
- Noted potential stability issues with large unsigned number division and memory safety during interrupt handling

amichai-bd (Reviewer):
- Flagged inefficient division algorithms with comments: "Wow - this is why it takes so long! please change to a better algorithm"
- Requested terminology clarification (pointer vs. address; register file pointer vs. address)
- Confirmed test was included: "BIG_CORE -cfg big_core_rv32im with reference model"

Linked Issue:
#648: add M extension to big_core - marked for closure