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honor the 'ready' signal from the GCD output #153

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honor the 'ready' signal from the GCD output #153

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honor the 'ready' signal from the GCD output
wunderabt May 17, 2021
030bd81
use a 8to1 clock divider to force some backpressure but it elaborates…
wunderabt May 19, 2021
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50 changes: 40 additions & 10 deletions 2.6_chiseltest.ipynb
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Original file line number Diff line number Diff line change
Expand Up @@ -420,26 +420,26 @@
" val x = Reg(UInt())\n",
" val y = Reg(UInt())\n",
" val busy = RegInit(false.B)\n",
" val resultValid = RegInit(false.B)\n",
"\n",
" input.ready := ! busy\n",
" output.valid := resultValid\n",
" output.bits := DontCare\n",
" output.valid := false.B\n",
"\n",
" when(busy) {\n",
" // during computation keep subtracting the smaller from the larger\n",
" when(x > y) {\n",
" x := x - y\n",
" when(y > 0.U) {\n",
" when(x > y) {\n",
" x := x - y\n",
" }.otherwise {\n",
" y := y - x\n",
" }\n",
" }.otherwise {\n",
" y := y - x\n",
" }\n",
" when(y === 0.U) {\n",
" // when y becomes zero computation is over, signal valid data to output\n",
" output.bits.value1 := xInitial\n",
" output.bits.value2 := yInitial\n",
" output.bits.gcd := x\n",
" output.valid := true.B\n",
" busy := false.B\n",
" busy := ! output.ready\n",
" }\n",
" }.otherwise {\n",
" when(input.valid) {\n",
Expand All @@ -450,7 +450,7 @@
" xInitial := bundle.value1\n",
" yInitial := bundle.value2\n",
" busy := true.B\n",
" resultValid := false.B\n",
" output.valid := false.B\n",
" }\n",
" }\n",
"}\n"
Expand Down Expand Up @@ -503,6 +503,36 @@
"}\n"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"// test for backpressure\n",
"test(new DecoupledGcd(16)) { dut =>\n",
" dut.input.initSource().setSourceClock(dut.clock)\n",
" dut.output.initSink().setSinkClock(dut.clock)\n",
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@wunderabt wunderabt May 17, 2021 •
edited
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What I want to do is to use slower clock for the sink so that there is greater chance that a fork + join approach runs into a backpressure scenario but I don't know how to write a ClockDivider here? @edwardcwang or @ducky64 do you maybe have some directions?

"\n",
" val testValues = for { x <- 1 to 10; y <- 1 to 10} yield (x, y)\n",
" val inputSeq = testValues.map { case (x, y) =>\n",
" (new GcdInputBundle(16)).Lit(_.value1 -> x.U, _.value2 -> y.U)\n",
" }\n",
" val resultSeq = testValues.map { case (x, y) =>\n",
" new GcdOutputBundle(16).Lit(_.value1 -> x.U, _.value2 -> y.U, _.gcd -> BigInt(x).gcd(BigInt(y)).U)\n",
" }\n",
"\n",
" for((inputVal, resultVal) <- inputSeq zip resultSeq) {\n",
" dut.input.enqueueNow(inputVal)\n",
" dut.output.ready.poke(false.B)\n",
" for(_ <- 0 to 10) {\n",
" dut.clock.step(1)\n",
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this is my poor mans solution for the clock divider - set the ouput in a non-ready state and idle for come cycles.

" }\n",
" dut.output.expectDequeueNow(resultVal)\n",
" }\n",
"}"
]
},
{
"cell_type": "markdown",
"metadata": {},
Expand Down Expand Up @@ -531,4 +561,4 @@
},
"nbformat": 4,
"nbformat_minor": 2
}
}