From 004cac91e1759a39f41df5e5cd6de52ee49e29c5 Mon Sep 17 00:00:00 2001
From: David Harris <david_harris@hmc.edu>
Date: Sun, 4 Jul 2021 19:17:15 -0400
Subject: [PATCH] Simplified PLIC with generate
---
wally-pipelined/src/uncore/plic.sv | 44 ++++++++++++------------------
1 file changed, 18 insertions(+), 26 deletions(-)
diff --git a/wally-pipelined/src/uncore/plic.sv b/wally-pipelined/src/uncore/plic.sv
index 70c72189..ef7ecdd5 100644
--- a/wally-pipelined/src/uncore/plic.sv
+++ b/wally-pipelined/src/uncore/plic.sv
@@ -170,24 +170,18 @@ module plic (
for (i=1; i<=N; i=i+1) begin: pendingbit
// *** make sure that this synthesizes into N decoders, not 7*N 3-bit equality comparators (right?)
assign pendingArray[j][i] = (intPriority[i]==j) & intEn[i] & intPending[i];
-/* assign pendingArray[6][i] = (intPriority[i]==6) & intEn[i] & intPending[i];
- assign pendingArray[5][i] = (intPriority[i]==5) & intEn[i] & intPending[i];
- assign pendingArray[4][i] = (intPriority[i]==4) & intEn[i] & intPending[i];
- assign pendingArray[3][i] = (intPriority[i]==3) & intEn[i] & intPending[i];
- assign pendingArray[2][i] = (intPriority[i]==2) & intEn[i] & intPending[i];
- assign pendingArray[1][i] = (intPriority[i]==1) & intEn[i] & intPending[i]; */
end
end
endgenerate
// pending array, except grouped by priority
-/* assign pendingPGrouped[7:1] = {|pendingArray[7],
+ assign pendingPGrouped[7:1] = {|pendingArray[7],
|pendingArray[6],
|pendingArray[5],
|pendingArray[4],
|pendingArray[3],
|pendingArray[2],
- |pendingArray[1]}; */
- assign pendingPGrouped = pendingArray.or;
+ |pendingArray[1]};
+ //assign pendingPGrouped = pendingArray.or;
// pendingPGrouped, except only topmost priority is active
assign pendingMaxP[7:1] = {pendingPGrouped[7],
@@ -206,26 +200,24 @@ module plic (
| ({N{pendingMaxP[2]}} & pendingArray[2])
| ({N{pendingMaxP[1]}} & pendingArray[1]);
// find the lowest ID amongst active interrupts at the highest priority
- genvar k;
- // *** verify that this synthesizes to a reasonable priority encoder and that j doesn't actually exist in hardware
- generate
- always_comb begin
- intClaim = 6'b0;
- for(k=N; k>0; k=k-1) begin:priorityenc
- if(pendingRequestsAtMaxP[k]) intClaim = k;
- end
+ int k;
+ // *** verify that this synthesizes to a reasonable priority encoder and that k doesn't actually exist in hardware
+ always_comb begin
+ intClaim = 6'b0;
+ for(k=N; k>0; k=k-1) begin
+ if(pendingRequestsAtMaxP[k]) intClaim = k[5:0];
end
- endgenerate
+ end
// create threshold mask
- always_comb begin
- threshMask[7] = ~(7==intThreshold);
- threshMask[6] = ~(6==intThreshold) & threshMask[7];
- threshMask[5] = ~(5==intThreshold) & threshMask[6];
- threshMask[4] = ~(4==intThreshold) & threshMask[5];
- threshMask[3] = ~(3==intThreshold) & threshMask[4];
- threshMask[2] = ~(2==intThreshold) & threshMask[3];
- threshMask[1] = ~(1==intThreshold) & threshMask[2];
+ always_comb begin
+ threshMask[7] = (intThreshold != 7);
+ threshMask[6] = (intThreshold != 6) & threshMask[7];
+ threshMask[5] = (intThreshold != 5) & threshMask[6];
+ threshMask[4] = (intThreshold != 4) & threshMask[5];
+ threshMask[3] = (intThreshold != 3) & threshMask[4];
+ threshMask[2] = (intThreshold != 2) & threshMask[3];
+ threshMask[1] = (intThreshold != 1) & threshMask[2];
end
// is the max priority > threshold?
// *** would it be any better to first priority encode maxPriority into binary and then ">" with threshold?