[pwm,rtl] Rewrite two write-enables more explicitly #25062
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rswarbrick
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vogelpi
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Nov 12, 2024
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This looks good, thanks @rswarbrick !
But can you please combine the two commits? Both commits touch the very same file and they both implement a very similar change without functional impact. I don't think we would ever want to undo only one of them.
The behaviour will be the same, but the first change avoids an expression coverage hole being reported for `blink_en_i == 0` and `blink_ctr_q == 1`. This can't actually happen: `blink_ctr_q` can only be updated by being set to `blink_ctr_d` (on this line). If `blink_en_i` is false then `blink_ctr_d == 0`. The only other way to reach the item would be to have incremented `blink_ctr_q` and then disabled blink. But disabling blink needs a register write, which will set a bit in `clr_blink_cntr` in `pwm_core`, which means that `clr_blink_cntr_i` is true, zeroing `blink_ctr_q`. Coding this write-enable more explicitly gets rid of the expression coverage item. The second change covers two further coverage holes, that have htbt_ctr_q and the write predicate false (either because blink_en_i is false or htbt_en_i is false). As before, this isn't possible. If the predicate is not true then htbt_ctr_d will be zero (so htbt_ctr_q cannot become nonzero). If it was nonzero before and we are changing the predicate to become false, the register write will cause clr_blink_cntr_i to go high, zeroing htbt_ctr_q. Signed-off-by: Rupert Swarbrick <[email protected]>
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Good point: done. Would you mind doing the "unauthorized changes dance"? |
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CHANGE AUTHORIZED: hw/ip/pwm/rtl/pwm_chan.sv |
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This is actually two commits, which both behave essentially the same (with similar notes). The commit message for the first is:
The behaviour will be the same, but it avoids an expression coverage hole being reported for
blink_en_i == 0andblink_ctr_q == 1. This can't actually happen:blink_ctr_qcan only be updated by being set toblink_ctr_d(on this line). Ifblink_en_iis false thenblink_ctr_d == 0.The only other way to reach the item would be to have incremented
blink_ctr_qand then disabled blink. But disabling blink needs a register write, which will set a bit inclr_blink_cntrinpwm_core, which means thatclr_blink_cntr_iis true, zeroingblink_ctr_q.Coding this write-enable more explicitly gets rid of the expression coverage item.