| commit | 22af1e8d98b1a1753af0e34ef37ed333fc082c4a | [log] [tgz] |
|---|---|---|
| author | Rupert Swarbrick <rswarbrick@lowrisc.org> | Wed Oct 13 15:46:39 2021 +0100 |
| committer | Rupert Swarbrick <rswarbrick@gmail.com> | Thu Oct 14 09:39:38 2021 +0100 |
| tree | 47937ce504d5dc4a049623b068ba0c1ccfa5db06 | |
| parent | 4a8e2ce55209660d86d89f4cb054165a362292b8 [diff] |
[otbn,dv] Sample RTL signals on first cycle of instruction We sample various internal RTL signals in order to do coverage collection. These are supposed to be "the value of the state just before the instruction ran". Most of the time, this is the same as "the value of the state just before the last cycle of running the instruction", but that's not quite always true. In particular, consider the following instruction: BN.LID x1, 0(x0) This reads from the call stack (x1) in order to get a destination address. With the current RTL implementation, the call stack pop happens on the first cycle which means that the previous code was sampling too late and saw an empty call stack. We wouldn't have noticed, except that the checks on "lockl_x1_uflow" in otbn_env_cov were failing (because we thought we should have seen a call stack underflow and the RTL disagreed). Fixes #8587. Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
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