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Removed 1 cycle delay on store miss.

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Changed some logic to partially support atomics.
This commit is contained in:
Ross Thompson 2021-07-30 14:00:51 -05:00
parent b9f8c25280
commit 89a7b38f79
1 changed files with 18 additions and 65 deletions
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77
wally-pipelined/src/cache/dcache.sv vendored
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@ -146,7 +146,6 @@ module dcache
logic PreCntEn; logic PreCntEn;
logic CntEn; logic CntEn;
logic CntReset; logic CntReset;
logic CPUBusy, PreviousCPUBusy;
logic SelEvict; logic SelEvict;
logic LRUWriteEn; logic LRUWriteEn;
@ -364,27 +363,7 @@ module dcache
.d(LSUData), .d(LSUData),
.q(SavedReadDataM)); .q(SavedReadDataM));
// *** BUG remove mux assign ReadDataM = LSUData;
mux2 #(`XLEN)
ReadDataMMux(.d0(LSUData),
.d1(SavedReadDataM),
.s(1'b0),
.y(ReadDataM));
// This is a confusing point.
// The final read data should be updated only if the CPU's StallWtoDCache is low
// which means the CPU is ready to take data. Or if the CPU just became
// busy. Then when we exit CPU_BUSY we want to ensure the data is not
// updated, this is ~PreviousCPUBusy.
// also must update if cpu stalled and processing a read miss
// which occurs if in state miss read word delay.
assign CPUBusy = CurrState == STATE_CPU_BUSY;
flop #(1) CPUBusyReg(.clk, .d(CPUBusy), .q(PreviousCPUBusy));
// write path // write path
subwordwrite subwordwrite(.HRDATA(ReadDataWordM), subwordwrite subwordwrite(.HRDATA(ReadDataWordM),
@ -398,7 +377,7 @@ module dcache
logic [`XLEN-1:0] AMOResult; logic [`XLEN-1:0] AMOResult;
amoalu amoalu(.srca(ReadDataM), .srcb(WriteDataM), .funct(Funct7M), .width(Funct3M[1:0]), amoalu amoalu(.srca(ReadDataM), .srcb(WriteDataM), .funct(Funct7M), .width(Funct3M[1:0]),
.result(AMOResult)); .result(AMOResult));
mux2 #(`XLEN) wdmux(FinalWriteDataM, AMOResult, SelAMOWrite & AtomicM[1], FinalAMOWriteDataM); mux2 #(`XLEN) wdmux(FinalWriteDataM, AMOResult, AtomicM[1], FinalAMOWriteDataM);
end else end else
assign FinalAMOWriteDataM = FinalWriteDataM; assign FinalAMOWriteDataM = FinalWriteDataM;
endgenerate endgenerate
@ -513,26 +492,22 @@ module dcache
DCacheStall = 1'b1; DCacheStall = 1'b1;
NextState = STATE_PTW_READY; NextState = STATE_PTW_READY;
end end
/* -----\/----- EXCLUDED -----\/-----
else if(SelPTW) begin
// Now we have activated the ptw.
// Do not assert Stall as we are now directing the stall the ptw.
NextState = STATE_PTW_READY;
CommittedM = 1'b1;
end
-----/\----- EXCLUDED -----/\----- */
// amo hit // amo hit
/* -----\/----- EXCLUDED -----\/----- else if(AtomicM[1] & (&MemRWM) & CacheableM & ~(ExceptionM | PendingInterruptM) & CacheHit & ~DTLBMissM) begin
else if(|AtomicM & CacheableM & ~(ExceptionM | PendingInterruptM) & CacheHit & ~DTLBMissM) begin SelAdrM = 2'b01;
NextState = STATE_AMO_UPDATE; DCacheStall = 1'b0;
DCacheStall = 1'b1; SRAMWordWriteEnableM = 1'b1;
SetDirtyM = 1'b1;
LRUWriteEn = 1'b1;
if(StallWtoDCache) begin if(StallWtoDCache) begin
NextState = STATE_CPU_BUSY; NextState = STATE_CPU_BUSY;
SelAdrM = 2'b01; SelAdrM = 2'b01;
else NextState = STATE_AMO_UPDATE;
end end
-----/\----- EXCLUDED -----/\----- */ else begin
NextState = STATE_READY;
end
end
// read hit valid cached // read hit valid cached
else if(MemRWM[1] & CacheableM & ~(ExceptionM | PendingInterruptM) & CacheHit & ~DTLBMissM) begin else if(MemRWM[1] & CacheableM & ~(ExceptionM | PendingInterruptM) & CacheHit & ~DTLBMissM) begin
DCacheStall = 1'b0; DCacheStall = 1'b0;
@ -592,22 +567,6 @@ module dcache
else NextState = STATE_READY; else NextState = STATE_READY;
end end
STATE_AMO_UPDATE: begin
NextState = STATE_AMO_WRITE;
SaveSRAMRead = 1'b1;
SRAMWordWriteEnableM = 1'b1; // pipelined 1 cycle
end
STATE_AMO_WRITE: begin
SelAMOWrite = 1'b1;
if(StallWtoDCache) begin
NextState = STATE_CPU_BUSY;
SelAdrM = 2'b01;
end
else begin
NextState = STATE_READY;
end
end
STATE_MISS_FETCH_WDV: begin STATE_MISS_FETCH_WDV: begin
DCacheStall = 1'b1; DCacheStall = 1'b1;
PreCntEn = 1'b1; PreCntEn = 1'b1;
@ -649,12 +608,12 @@ module dcache
SelAdrM = 2'b01; SelAdrM = 2'b01;
DCacheStall = 1'b1; DCacheStall = 1'b1;
CommittedM = 1'b1; CommittedM = 1'b1;
if (MemRWM[1]) begin if (MemRWM[0]) begin // handles stores and amo write.
NextState = STATE_MISS_WRITE_WORD;
end else begin
NextState = STATE_MISS_READ_WORD_DELAY; NextState = STATE_MISS_READ_WORD_DELAY;
// delay state is required as the read signal MemRWM[1] is still high when we // delay state is required as the read signal MemRWM[1] is still high when we
// return to the ready state because the cache is stalling the cpu. // return to the ready state because the cache is stalling the cpu.
end else begin
NextState = STATE_MISS_WRITE_WORD;
end end
end end
@ -675,14 +634,8 @@ module dcache
SRAMWordWriteEnableM = 1'b1; SRAMWordWriteEnableM = 1'b1;
SetDirtyM = 1'b1; SetDirtyM = 1'b1;
SelAdrM = 2'b01; SelAdrM = 2'b01;
DCacheStall = 1'b1;
CommittedM = 1'b1; CommittedM = 1'b1;
LRUWriteEn = 1'b1; LRUWriteEn = 1'b1;
NextState = STATE_MISS_WRITE_WORD_DELAY;
end
STATE_MISS_WRITE_WORD_DELAY: begin
CommittedM = 1'b1;
if(StallWtoDCache) begin if(StallWtoDCache) begin
NextState = STATE_CPU_BUSY; NextState = STATE_CPU_BUSY;
SelAdrM = 2'b01; SelAdrM = 2'b01;