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Found the complex TrapM giving back the wrong instruction bug.

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As I was reviewing the busfsm I found a typo.

  assign UnCachedLSUBusRead = (BusCurrState == STATE_BUS_READY & UnCachedAccess & LSURWM[1] & IgnoreRequest) |
							  (BusCurrState == STATE_BUS_UNCACHED_READ);

It should be

  assign UnCachedLSUBusRead = (BusCurrState == STATE_BUS_READY & UnCachedAccess & LSURWM[1] & ~IgnoreRequest) |
							  (BusCurrState == STATE_BUS_UNCACHED_READ);

There is a ~ missing before IgnoreRequest. I restarted the FPGA and had it trigger on the specific faulting event.  Sure enough the bus makes an IFUBusRead, which UncachedLSUBusRead feeds into.   The specific instruction in the fetch stage had an ITLBMiss with a physical address in an unmapped area which is interpreted as an uncached operation.  IgnoreRequest is is high if there is a TrapM | ITLBMissF.  Without the & ~IgnoreRequest the invalid address translation makes the request.
This commit is contained in:
Ross Thompson 2022-04-11 13:07:52 -05:00
parent 9685365d2e
commit 70e207e010
1 changed files with 1 additions and 1 deletions
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pipelined/src/lsu/busfsm.sv
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@ -135,7 +135,7 @@ module busfsm #(parameter integer WordCountThreshold,
(BusCurrState == STATE_BUS_UNCACHED_WRITE) |
(BusCurrState == STATE_BUS_WRITE);
assign UnCachedLSUBusRead = (BusCurrState == STATE_BUS_READY & UnCachedAccess & LSURWM[1] & IgnoreRequest) |
assign UnCachedLSUBusRead = (BusCurrState == STATE_BUS_READY & UnCachedAccess & LSURWM[1] & ~IgnoreRequest) |
(BusCurrState == STATE_BUS_UNCACHED_READ);
assign LSUBusRead = UnCachedLSUBusRead | (BusCurrState == STATE_BUS_FETCH) | (BusCurrState == STATE_BUS_READY & DCacheFetchLine);