| commit | fafeaf223e11aa36e33606b9aadca4cd6b175863 | [log] [tgz] |
|---|---|---|
| author | Rupert Swarbrick <rswarbrick@lowrisc.org> | Tue Jan 04 14:42:44 2022 +0000 |
| committer | Rupert Swarbrick <rswarbrick@gmail.com> | Tue Jan 04 17:17:27 2022 +0000 |
| tree | cdcd44991a8cff86c4f87474ae366e56615a0c79 | |
| parent | 8eb8697ed76b60bf925def32c50ea53a02a26eab [diff] |
[otbn] Widen prefetch_loop_end_addr to avoid overflow There's an amusing bug that you can trigger if you have something like loopi 123, 1025 The problem is that 1025 instructions (the loop body length) works out as 4096 + 4 bytes, so the correct value of prefetch_loop_end_addr is something like old_addr + 4096 + 4. Unfortunately, 4096 is the size of IMEM so we were truncating this to just old_addr + 4. This meant that the prefetch stage thought that the following instruction was at the end of the loop and predicted a back edge. Eventually, we failed the NoAddressMismatch assertion in otbn_instruction_fetch.sv. The fix is to pass one extra bit in the address, just like we already do with the check in the loop controller itself. Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
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