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Reverted to fetched the demand cache line first then doing the eviction. This is important because of an optimization in the replacement policy. The replacement policy updates the LRU 1 cycle late and reads the LRU 1 cycle late for critical path timing. This means doing the eviction first requires an initial 1 cycle delay but this delay has to be applied to all misses because we don't know if an eviction is required. Since reading the demand line first is logically ok so long as it is not written to the sram until after the eviction.

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This commit is contained in:
Ross Thompson 2022-07-19 22:42:25 -05:00
parent ffda64587c
commit 6c8ac7851e
2 changed files with 17 additions and 11 deletions
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6
pipelined/regression/wave.do
View File

@ -316,8 +316,10 @@ add wave -noupdate -expand -group lsu -expand -group dcache -group status /testb
add wave -noupdate -expand -group lsu -expand -group dcache -group status -color {Medium Orchid} /testbench/dut/core/lsu/bus/dcache/dcache/CacheHit
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {Memory Side} /testbench/dut/core/lsu/bus/dcache/dcache/CacheFetchLine
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {Memory Side} /testbench/dut/core/lsu/bus/dcache/dcache/CacheWriteLine
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {Memory Side} /testbench/dut/core/lsu/bus/dcache/dcache/CacheBusAdr
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {Memory Side} /testbench/dut/core/lsu/bus/dcache/dcache/CacheBusWriteData
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {Memory Side} /testbench/dut/core/lsu/bus/dcache/dcache/CacheBusAck
add wave -noupdate -expand -group lsu -expand -group dcache -expand -group {Memory Side} /testbench/dut/core/lsu/bus/dcache/dcache/ReadDataWord
add wave -noupdate -expand -group lsu -expand -group dcache /testbench/dut/core/lsu/bus/dcache/dcache/FlushWay
add wave -noupdate -expand -group lsu -group dtlb /testbench/dut/core/lsu/dmmu/dmmu/tlb/tlb/VAdr
add wave -noupdate -expand -group lsu -group dtlb /testbench/dut/core/lsu/dmmu/dmmu/tlb/tlb/tlbcontrol/EffectivePrivilegeMode
@ -515,7 +517,7 @@ add wave -noupdate /testbench/dut/core/lsu/VIRTMEM_SUPPORTED/lsuvirtmem/hptw/Upd
add wave -noupdate {/testbench/dut/core/ifu/bus/icache/icache/CacheWays[0]/FinalByteMask}
add wave -noupdate {/testbench/dut/core/ifu/bus/icache/icache/CacheWays[0]/SelectedWriteWordEn}
TreeUpdate [SetDefaultTree]
WaveRestoreCursors {{Cursor 5} {307575 ns} 1} {{Cursor 2} {307965 ns} 1} {{Cursor 3} {307661 ns} 0}
WaveRestoreCursors {{Cursor 5} {307575 ns} 1} {{Cursor 2} {307965 ns} 1} {{Cursor 3} {112734 ns} 0}
quietly wave cursor active 3
configure wave -namecolwidth 250
configure wave -valuecolwidth 314
@ -531,4 +533,4 @@ configure wave -griddelta 40
configure wave -timeline 0
configure wave -timelineunits ns
update
WaveRestoreZoom {0 ns} {3158332 ns}
WaveRestoreZoom {112550 ns} {112886 ns}

22
pipelined/src/cache/cachefsm.sv vendored
View File

@ -141,10 +141,12 @@ module cachefsm
STATE_READY: if(IgnoreRequest) NextState = STATE_READY;
else if(DoFlush) NextState = STATE_FLUSH;
else if(DoAnyHit & CPUBusy) NextState = STATE_CPU_BUSY;
else if(DoAnyMiss & VictimDirty) NextState = STATE_MISS_EVICT_DIRTY_START; // change
else if(DoAnyMiss & ~VictimDirty) NextState = STATE_MISS_FETCH_WDV; // change
else if(DoAnyMiss) NextState = STATE_MISS_FETCH_WDV;
//else if(DoAnyMiss & VictimDirty) NextState = STATE_MISS_EVICT_DIRTY_START; // change
//else if(DoAnyMiss & ~VictimDirty) NextState = STATE_MISS_FETCH_WDV; // change
else NextState = STATE_READY;
STATE_MISS_FETCH_WDV: if(CacheBusAck) NextState = STATE_MISS_WRITE_CACHE_LINE;
STATE_MISS_FETCH_WDV: if(CacheBusAck & ~VictimDirty) NextState = STATE_MISS_WRITE_CACHE_LINE;
else if(CacheBusAck & VictimDirty) NextState = STATE_MISS_EVICT_DIRTY_START;
else NextState = STATE_MISS_FETCH_WDV;
STATE_MISS_WRITE_CACHE_LINE: NextState = STATE_READY;
STATE_MISS_READ_WORD: if(CacheRW[0] & ~AMO) NextState = STATE_MISS_WRITE_WORD;
@ -153,9 +155,11 @@ module cachefsm
else NextState = STATE_READY;
STATE_MISS_WRITE_WORD: if(CPUBusy) NextState = STATE_CPU_BUSY;
else NextState = STATE_READY;
STATE_MISS_EVICT_DIRTY_START: NextState = STATE_MISS_EVICT_DIRTY; // start needed for the delayed lru update.
STATE_MISS_EVICT_DIRTY: if(CacheBusAck) NextState = STATE_MISS_EVICT_DIRTY_DONE;
STATE_MISS_EVICT_DIRTY: if(CacheBusAck) NextState = STATE_MISS_WRITE_CACHE_LINE;
else NextState = STATE_MISS_EVICT_DIRTY;
STATE_MISS_EVICT_DIRTY_START: NextState = STATE_MISS_EVICT_DIRTY; // start needed for the delayed lru update.
// STATE_MISS_EVICT_DIRTY: if(CacheBusAck) NextState = STATE_MISS_EVICT_DIRTY_DONE;
// else NextState = STATE_MISS_EVICT_DIRTY;
STATE_MISS_EVICT_DIRTY_DONE: NextState = STATE_MISS_FETCH_WDV;
STATE_CPU_BUSY: if(CPUBusy) NextState = STATE_CPU_BUSY;
else NextState = STATE_READY;
@ -199,7 +203,7 @@ module cachefsm
assign LRUWriteEn = (CurrState == STATE_READY & DoAnyHit) |
(CurrState == STATE_MISS_WRITE_CACHE_LINE);
// Flush and eviction controls
assign SelEvict = (CurrState == STATE_READY & DoAnyMiss & VictimDirty) |
assign SelEvict = //(CurrState == STATE_MISS_FETCH_WDV & CacheBusAck & VictimDirty) |
(CurrState == STATE_MISS_EVICT_DIRTY_START) |
(CurrState == STATE_MISS_EVICT_DIRTY);
assign SelFlush = (CurrState == STATE_FLUSH) | (CurrState == STATE_FLUSH_CHECK) |
@ -213,9 +217,9 @@ module cachefsm
assign FlushAdrCntRst = (CurrState == STATE_READY);
assign FlushWayCntRst = (CurrState == STATE_READY) | (CurrState == STATE_FLUSH_INCR);
// Bus interface controls
assign CacheFetchLine = (CurrState == STATE_READY & DoAnyMiss & ~VictimDirty) |
(CurrState == STATE_MISS_EVICT_DIRTY_DONE);
assign CacheWriteLine = (CurrState == STATE_READY & DoAnyMiss & VictimDirty) |
assign CacheFetchLine = (CurrState == STATE_READY & DoAnyMiss);
// assign CacheWriteLine = (CurrState == STATE_MISS_FETCH_WDV & VictimDirty & CacheBusAck) |
assign CacheWriteLine = (CurrState == STATE_MISS_EVICT_DIRTY_START) |
(CurrState == STATE_FLUSH_CHECK & VictimDirty);
// handle cpu stall.
assign restore = ((CurrState == STATE_CPU_BUSY)) & ~`REPLAY;