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A more sophisticated RAS protection delay.

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Saturate down, and also predict with old push value if there is more
than 6 cycles of delay.
This commit is contained in:
Jonathan Woodruff
2022-03-08 15:17:54 +00:00
parent 064cd22114
commit bbdcf6dde9
2 changed files with 15 additions and 7 deletions
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3
src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv
View File

@@ -705,6 +705,9 @@ module mkFetchStage(FetchStage);
`endif
`ifdef NO_SPEC_RSB_PUSH
Bool delayForPop = ras.pendingPush && anyReturns;
rule showDelayForPop(delayForPop);
$display("RAS delayForPop; ras.pendingPush: %x, anyReturns: %x %d", ras.pendingPush, anyReturns, cur_cycle);
endrule
delay_epoch = delay_epoch || delayForPop;
`endif

19
src_Core/RISCY_OOO/procs/lib/Ras.bsv
View File

@@ -69,11 +69,11 @@ module mkRas(ReturnAddrStack) provisos(NumAlias#(TExp#(TLog#(RasEntries)), RasEn
// head points past valid data
// to gracefully overflow, head is allowed to overflow to 0 and overwrite the oldest data
Ehr#(TAdd#(SupSize, 3), RasIndex) head <- mkEhr(0);
Ehr#(3, RasIndex) pendingPushReg <- mkEhr(0);
Ehr#(4, UInt#(3)) pendingPushReg <- mkEhr(0);
Reg#(Bit#(6)) pendingPushDelay <- mkReg(0);
rule updatePendingPushDelay(pendingPushReg[2] != 0);
if (pendingPushDelay > 8) begin
rule updatePendingPushDelay;
if (pendingPushDelay > 60 || pendingPushReg[2] == 0) begin
pendingPushReg[2] <= 0;
pendingPushDelay <= 0;
end else pendingPushDelay <= pendingPushDelay + 1;
@@ -93,7 +93,11 @@ module mkRas(ReturnAddrStack) provisos(NumAlias#(TExp#(TLog#(RasEntries)), RasEn
for(Integer i = 0; i < valueof(SupSize); i = i+1) begin
rasIfc[i] = (interface RAS;
method CapMem first;
return stack[head[i]][0];
// If pendingPush is not zero, just take whetever was in the memory, as it is more likely
// to be correct than an unsynchronised entry (in case we keep calling the same function).
RasIndex pendingOffset = zeroExtend(pack(pendingPushReg[0]));
RasIndex h = head[i] + pendingOffset;
return stack[h][0];
endmethod
method ActionValue#(RasIndex) pop(Bool doPop);
RasIndex h = head[i];
@@ -110,18 +114,19 @@ module mkRas(ReturnAddrStack) provisos(NumAlias#(TExp#(TLog#(RasEntries)), RasEn
pendingPushReg[0]._write(pendingPushReg[0] + 1);
$display("RAS willPushReg<-%d", pendingPushReg[0] + 1);
endmethod
method Bool pendingPush = (pendingPushReg[0] != 0);
method Bool pendingPush = (pendingPushReg[0] > 0 && pendingPushDelay < 6);
method Action push(CapMem pushAddr);
Reg#(RasIndex) h = head[valueof(SupSize) + 2];
stack[h+1][1] <= pushAddr;
$display("RAS push head<-%d, val:%x, willPushReg<-%d", h+1, pushAddr, pendingPushReg[1] - 1);
$display("RAS push head<-%d, val:%x, willPushReg<-%d", h+1, pushAddr, boundedMinus(pendingPushReg[1], 1));
h <= h+1;
if (pendingPushReg[1] != 0) pendingPushReg[1] <= pendingPushReg[1] - 1;
if (pendingPushReg[1] != 0) pendingPushReg[1] <= boundedMinus(pendingPushReg[1], 1);
endmethod
method Action setHead(RasIndex h);
head[valueof(SupSize)] <= h;
pendingPushReg[3] <= 0;
$display("RAS fixup head<-%d", h);
endmethod