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handled tag engine edge case

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This commit is contained in:
Yehowshua Immanuel 2025-04-04 15:09:56 -04:00
parent 271148e538
commit ca59e6eaec
2 changed files with 57 additions and 23 deletions
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59
bs/TagEngine.bs
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@ -7,6 +7,7 @@ import Vector
import Util
import FIFO
import FIFOF
import SpecialFIFOs
#define UIntLog2N(n) (UInt (TLog n))
@ -23,7 +24,7 @@ mkTagEngine =
do
let reifiedNumTags = fromInteger |> valueOf numTags
-- we really only use tagUsageTracker after emptying out our
-- we really only use tagUsageTracker after emptying out our
-- `initialTagDistributor` buffer
tagUsageTracker :: Vector numTags (Reg Bool)
tagUsageTracker <- replicateM |> mkReg False
@ -32,13 +33,19 @@ mkTagEngine =
-- reset, we can pretend as if the buffer within our tagFIFO is populated
-- with sequentially incrementing values(starting from 0) on reset
-- by having our tag engine effectively return the value of a decrementing
-- counter initialized to (numTags - 1) for the first n tag requests made
-- counter initialized to (numTags - 1) for the first n tag requests made
-- to TagEngine where `n := numTags`.
initialTagDistributor :: (Reg (Maybe UIntLog2N(numTags)))
initialTagDistributor <- mkReg |> Just |> reifiedNumTags - 1
retireTag :: Wire UIntLog2N(numTags)
retireTag <- mkWire
validatedTagToRetire :: FIFO UIntLog2N(numTags)
validatedTagToRetire <- mkBypassFIFO
updateUsageRetireTag :: RWire UIntLog2N(numTags)
updateUsageRetireTag <- mkRWire
updateUsageRequestTag :: RWire UIntLog2N(numTags)
updateUsageRequestTag <- mkRWire
tagFIFO :: FIFOF UIntLog2N(numTags)
tagFIFO <- mkSizedFIFOF reifiedNumTags
@ -51,12 +58,39 @@ mkTagEngine =
do
$display "tagUsageTracker : " (fshow |> readVReg tagUsageTracker)
debugOnce := False
"update_usage_just_retire": when
Just tag <- updateUsageRetireTag.wget,
Nothing <- updateUsageRequestTag.wget ==>
do
$display $time " tagUsageTracker after update retire: " (fshow |> readVReg tagUsageTracker)
(select tagUsageTracker tag) := False
"update_usage_just_request": when
Nothing <- updateUsageRetireTag.wget,
Just tag <- updateUsageRequestTag.wget ==>
do
$display $time " tagUsageTracker after update request: " (fshow |> readVReg tagUsageTracker)
(select tagUsageTracker tag) := True
"update_usage_request_and_retire": when
Just retireTag <- updateUsageRetireTag.wget,
Just requestTag <- updateUsageRequestTag.wget ==>
do
$display $time " tagUsageTracker after update request and retire: " (fshow |> readVReg tagUsageTracker)
let
tagUsageTrackerInner = readVReg tagUsageTracker
tagUsageTracker' = update tagUsageTrackerInner requestTag True
tagUsageTracker'' = update tagUsageTracker' retireTag False
writeVReg tagUsageTracker tagUsageTracker''
"retire_tags": when True ==>
do
$display "firing retire_tags" (fshow retireTag)
tagFIFO.enq retireTag
(select tagUsageTracker retireTag) := False
let tagToRetire = validatedTagToRetire.first
$display "firing retire_tags" (fshow tagToRetire)
validatedTagToRetire.deq
tagFIFO.enq tagToRetire
updateUsageRetireTag.wset tagToRetire
return $
interface TagEngine
@ -67,18 +101,19 @@ mkTagEngine =
case initialTagDistributor of
Just 0 -> do
initialTagDistributor := Nothing
(select tagUsageTracker 0) := True
updateUsageRequestTag.wset 0
return 0
Just tag -> do
initialTagDistributor := Just |> tag - 1
(select tagUsageTracker tag) := True
updateUsageRequestTag.wset tag
return tag
Nothing -> do
let tag = tagFIFO.first
tagFIFO.deq
updateUsageRequestTag.wset tag
return tag
-- `retireTag` isn't guarded on tag validity(this would break Bluespec's safety model)
-- `retireTag` isn't guarded on tag validity(this would break Bluespec's safety model)
-- so it is advisable that the caller of `retireTag` only attempt to retire valid tags.
-- Internally, the tagEngine will keep a correct and consistent state since TagEngine
-- validates tags before attempting to retire them.
@ -90,6 +125,6 @@ mkTagEngine =
tagInUse = readReg (select tagUsageTracker tag)
if (tagValid && tagInUse)
then do
retireTag := tag
validatedTagToRetire.enq tag
else do
action {}