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Removed the hardware page table walker fault state from the icache so that the icache will only unstall CPU for 1 cycle.

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In the dcache we added a register to save the load read data in the event an itlb miss occurs concurrently with
the load in the memory stage.  Under this situation we need to record the load ReadDataM into a temporary register,
SavedReadDataM.  At this time the CPU is stall; however the walker is going to change the address in the dcache
which destroys this data.  When leaving the PTW_READY state via a walker instruction fault or ITLB write we select
this SavedReadDataM so that the CPU can capture it.
This commit is contained in:
Ross Thompson 2021-07-22 19:42:19 -05:00
parent 551e3491af
commit 3e916da36e
4 changed files with 51 additions and 28 deletions
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33
wally-pipelined/regression/wave.do
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@ -7,11 +7,12 @@ add wave -noupdate -expand -group {Execution Stage} /testbench/dut/hart/ifu/PCE
add wave -noupdate -expand -group {Execution Stage} /testbench/InstrEName
add wave -noupdate -expand -group {Execution Stage} /testbench/dut/hart/ifu/InstrE
add wave -noupdate -expand -group {Memory Stage} /testbench/dut/hart/priv/trap/InstrValidM
add wave -noupdate -expand -group {Memory Stage} /testbench/PCtextM
add wave -noupdate -expand -group {Memory Stage} /testbench/dut/hart/PCM
add wave -noupdate -expand -group {Memory Stage} /testbench/InstrMName
add wave -noupdate -expand -group {Memory Stage} /testbench/dut/hart/InstrM
add wave -noupdate -expand -group {Memory Stage} /testbench/dut/hart/lsu/MemAdrM
add wave -noupdate /testbench/dut/hart/ieu/dp/ResultM
add wave -noupdate /testbench/dut/hart/ieu/dp/ResultW
add wave -noupdate -expand -group HDU -group traps /testbench/dut/hart/priv/trap/InstrMisalignedFaultM
add wave -noupdate -expand -group HDU -group traps /testbench/dut/hart/priv/trap/InstrAccessFaultM
add wave -noupdate -expand -group HDU -group traps /testbench/dut/hart/priv/trap/IllegalInstrFaultM
@ -127,18 +128,18 @@ add wave -noupdate -group RegFile -group {write regfile mux} /testbench/dut/hart
add wave -noupdate -group RegFile -group {write regfile mux} /testbench/dut/hart/ieu/dp/CSRReadValW
add wave -noupdate -group RegFile -group {write regfile mux} /testbench/dut/hart/ieu/dp/ResultSrcW
add wave -noupdate -group RegFile -group {write regfile mux} /testbench/dut/hart/ieu/dp/ResultW
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/a
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/b
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/alucontrol
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/result
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/flags
add wave -noupdate -group alu -divider internals
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/overflow
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/carry
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/zero
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/neg
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/lt
add wave -noupdate -group alu /testbench/dut/hart/ieu/dp/alu/ltu
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/a
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/b
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/alucontrol
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/result
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/flags
add wave -noupdate -expand -group alu -divider internals
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/overflow
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/carry
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/zero
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/neg
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/lt
add wave -noupdate -expand -group alu /testbench/dut/hart/ieu/dp/alu/ltu
add wave -noupdate -group Forward /testbench/dut/hart/ieu/fw/Rs1D
add wave -noupdate -group Forward /testbench/dut/hart/ieu/fw/Rs2D
add wave -noupdate -group Forward /testbench/dut/hart/ieu/fw/Rs1E
@ -314,8 +315,6 @@ add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {CPU
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {CPU side} /testbench/dut/hart/lsu/dcache/AtomicM
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {CPU side} /testbench/dut/hart/lsu/dcache/CacheableM
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {CPU side} /testbench/dut/hart/lsu/dcache/WriteDataM
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {CPU side} /testbench/dut/hart/lsu/dcache/ReadDataW
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {CPU side} /testbench/dut/hart/lsu/dcache/StallW
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {CPU side} /testbench/dut/hart/lsu/dcache/DCacheStall
add wave -noupdate -expand -group lsu -expand -group dcache -group status /testbench/dut/hart/lsu/dcache/WayHit
add wave -noupdate -expand -group lsu -expand -group dcache -group status -color {Medium Orchid} /testbench/dut/hart/lsu/dcache/CacheHit
@ -365,7 +364,7 @@ add wave -noupdate -expand -group itlb /testbench/dut/hart/ifu/ITLBMissF
add wave -noupdate -expand -group itlb /testbench/dut/hart/ifu/immu/PhysicalAddress
add wave -noupdate /testbench/dut/hart/lsu/hptw/genblk1/PRegEn
TreeUpdate [SetDefaultTree]
WaveRestoreCursors {{Walk read is wrong} {26824 ns} 1} {{page table setup} {8167 ns} 1} {{eviction at wrong adr} {10128 ns} 1} {{Cursor 6} {41795656 ns} 0}
WaveRestoreCursors {{Walk read is wrong} {26824 ns} 1} {{page table setup} {8167 ns} 1} {{eviction at wrong adr} {10128 ns} 1} {{Cursor 6} {2898 ns} 0}
quietly wave cursor active 4
configure wave -namecolwidth 250
configure wave -valuecolwidth 297
@ -381,4 +380,4 @@ configure wave -griddelta 40
configure wave -timeline 0
configure wave -timelineunits ns
update
WaveRestoreZoom {41795482 ns} {41795818 ns}
WaveRestoreZoom {2835 ns} {2995 ns}

7
wally-pipelined/src/cache/ICacheCntrl.sv vendored
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@ -115,7 +115,6 @@ module ICacheCntrl #(parameter BLOCKLEN = 256)
localparam STATE_INVALIDATE = 'h12; // *** not sure if invalidate or evict? invalidate by cache block or address?
localparam STATE_TLB_MISS = 'h13;
localparam STATE_TLB_MISS_DONE = 'h14;
localparam STATE_INSTR_PAGE_FAULT = 'h15;
localparam AHBByteLength = `XLEN / 8;
@ -369,7 +368,7 @@ module ICacheCntrl #(parameter BLOCKLEN = 256)
end
STATE_TLB_MISS: begin
if (WalkerInstrPageFaultF) begin
NextState = STATE_INSTR_PAGE_FAULT;
NextState = STATE_READY;
ICacheStallF = 1'b0;
end else if (ITLBWriteF) begin
NextState = STATE_TLB_MISS_DONE;
@ -380,10 +379,6 @@ module ICacheCntrl #(parameter BLOCKLEN = 256)
STATE_TLB_MISS_DONE: begin
NextState = STATE_READY;
end
STATE_INSTR_PAGE_FAULT: begin
ICacheStallF = 1'b0;
NextState = STATE_READY;
end
default: begin
PCMux = 2'b01;
NextState = STATE_READY;

29
wally-pipelined/src/cache/dcache.sv vendored
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@ -60,6 +60,7 @@ module dcache
// from ptw
input logic SelPTW,
input logic WalkerPageFaultM,
output logic [`XLEN-1:0] LSUData,
// ahb side
output logic [`PA_BITS-1:0] AHBPAdr, // to ahb
output logic AHBRead,
@ -148,6 +149,11 @@ module dcache
logic LRUWriteEn;
logic CaptureDataM;
logic [`XLEN-1:0] SavedReadDataM;
logic SelSavedReadDataM;
typedef enum {STATE_READY,
STATE_MISS_FETCH_WDV,
@ -331,7 +337,24 @@ module dcache
subwordread subwordread(.HRDATA(ReadDataWordMuxM),
.HADDRD(MemPAdrM[2:0]),
.HSIZED({Funct3M[2], 1'b0, Funct3M[1:0]}),
.HRDATAMasked(ReadDataM));
.HRDATAMasked(LSUData));
assign CaptureDataM = ~SelPTW & MemRWM[1];
flopen #(`XLEN)
SavedReadDataReg(.clk,
.en(CaptureDataM),
.d(LSUData),
.q(SavedReadDataM));
mux2 #(`XLEN)
ReadDataMMux(.d0(LSUData),
.d1(SavedReadDataM),
.s(SelSavedReadDataM),
.y(ReadDataM));
// This is a confusing point.
// The final read data should be updated only if the CPU's StallWtoDCache is low
@ -457,6 +480,7 @@ module dcache
DCacheAccess = 1'b0;
DCacheMiss = 1'b0;
LRUWriteEn = 1'b0;
SelSavedReadDataM = 1'b0;
case (CurrState)
STATE_READY: begin
@ -659,6 +683,9 @@ module dcache
if (ITLBWriteF | WalkerInstrPageFaultF) begin
NextState = STATE_READY;
// this signal is gross. It is used to select the saved read data m when the
// CPU was stalled for an itlb miss with a simultaneous load.
SelSavedReadDataM = 1'b1;
end
// return to ready if page table walk completed.

4
wally-pipelined/src/lsu/lsu.sv
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@ -149,6 +149,7 @@ module lsu
logic FlushWtoDCache;
logic WalkerPageFaultM;
logic [`XLEN-1:0] LSUData;
hptw hptw(
.clk(clk),
@ -163,7 +164,7 @@ module lsu
.PageType,
.ITLBWriteF(ITLBWriteF),
.DTLBWriteM(DTLBWriteM),
.HPTWReadPTE(ReadDataM),
.HPTWReadPTE(LSUData),
.HPTWStall(HPTWStall),
.TranslationPAdr,
.HPTWRead(HPTWRead),
@ -303,6 +304,7 @@ module lsu
.VAdr(MemAdrM[11:0]),
.WriteDataM(WriteDataM),
.ReadDataM(ReadDataM),
.LSUData(LSUData),
.DCacheStall(DCacheStall),
.CommittedM(CommittedMfromDCache),
.DCacheMiss,