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plic implementation optimizations

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bbracker 2021-05-19 18:10:48 +00:00
parent 979a9bf037
commit bf6337f2f7
1 changed files with 28 additions and 35 deletions
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63
wally-pipelined/src/uncore/plic.sv
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@ -48,7 +48,7 @@ module plic (
localparam N=`PLIC_NUM_SRC; // should not exceed 63; does not inlcude source 0, which does not connect to anything according to spec
logic memwrite, memread, initTrans;
logic [27:0] entry, entryd;
logic [23:0] entry, entryd;
logic [31:0] Din, Dout;
logic [N:1] requests;
@ -66,12 +66,12 @@ module plic (
// =======
// AHB I/O
// =======
assign entry = {HADDR[27:2],2'b0};
assign entry = {HADDR[23:2],2'b0};
assign initTrans = HREADY & HSELPLIC & (HTRANS != 2'b00);
assign memread = initTrans & ~HWRITE;
// entryd and memwrite are delayed by a cycle because AHB controller waits a cycle before outputting write data
flopr #(1) memwriteflop(HCLK, ~HRESETn, initTrans & HWRITE, memwrite);
flopr #(28) entrydflop(HCLK, ~HRESETn, entry, entryd);
flopr #(24) entrydflop(HCLK, ~HRESETn, entry, entryd);
assign HRESPPLIC = 0; // OK
assign HREADYPLIC = 1'b1; // PLIC never takes >1 cycle to respond
@ -109,33 +109,33 @@ module plic (
end else begin
if (memwrite)
casez(entryd)
28'hc0000??: intPriority[entryd[7:2]] <= #1 Din[2:0];
24'h0000??: intPriority[entryd[7:2]] <= #1 Din[2:0];
`ifdef PLIC_NUM_SRC_LT_32
28'hc002000: intEn[N:1] <= #1 Din[N:1];
24'h002000: intEn[N:1] <= #1 Din[N:1];
`endif
`ifndef PLIC_NUM_SRC_LT_32
28'hc002000: intEn[31:1] <= #1 Din[31:1];
28'hc002004: intEn[N:32] <= #1 Din[31:0];
24'h002000: intEn[31:1] <= #1 Din[31:1];
24'h002004: intEn[N:32] <= #1 Din[31:0];
`endif
28'hc200000: intThreshold[2:0] <= #1 Din[2:0];
28'hc200004: intInProgress <= #1 intInProgress & ~(1'b1 << (Din[5:0]-1)); // lower "InProgress" to signify completion
24'h200000: intThreshold[2:0] <= #1 Din[2:0];
24'h200004: intInProgress <= #1 intInProgress & ~(1'b1 << (Din[5:0]-1)); // lower "InProgress" to signify completion
endcase
// reading
if (memread)
casez(entry)
28'hc0000??: Dout <= #1 {{(`XLEN-3){1'b0}},intPriority[entry[7:2]]};
24'h0000??: Dout <= #1 {{(`XLEN-3){1'b0}},intPriority[entry[7:2]]};
`ifdef PLIC_NUM_SRC_LT_32
28'hc001000: Dout <= #1 {{(31-N){1'b0}},intPending[N:1],1'b0};
28'hc002000: Dout <= #1 {{(31-N){1'b0}},intEn[N:1],1'b0};
24'h001000: Dout <= #1 {{(31-N){1'b0}},intPending[N:1],1'b0};
24'h002000: Dout <= #1 {{(31-N){1'b0}},intEn[N:1],1'b0};
`endif
`ifndef PLIC_NUM_SRC_LT_32
28'hc001000: Dout <= #1 {intPending[31:1],1'b0};
28'hc001004: Dout <= #1 {{(63-N){1'b0}},intPending[N:32]};
28'hc002000: Dout <= #1 {intEn[31:1],1'b0};
28'hc002004: Dout <= #1 {{(63-N){1'b0}},intEn[N:32]};
24'h001000: Dout <= #1 {intPending[31:1],1'b0};
24'h001004: Dout <= #1 {{(63-N){1'b0}},intPending[N:32]};
24'h002000: Dout <= #1 {intEn[31:1],1'b0};
24'h002004: Dout <= #1 {{(63-N){1'b0}},intEn[N:32]};
`endif
28'hc200000: Dout <= #1 {29'b0,intThreshold[2:0]};
28'hc200004: begin
24'h200000: Dout <= #1 {29'b0,intThreshold[2:0]};
24'h200004: begin
Dout <= #1 {26'b0,intClaim};
intInProgress <= #1 intInProgress | (1'b1 << (intClaim-1)); // claimed requests are currently in progress of being serviced until they are completed
end
@ -160,7 +160,7 @@ module plic (
// pending updates
// *** verify that this matches the expectations of the things that make requests (in terms of timing, edge-triggered vs level-triggered)
assign nextIntPending = (intPending | (requests & ~intInProgress)) // requests should raise intPending except when their service routine is already in progress
& ~(((entry == 28'hc200004) && memread) << (intClaim-1)); // clear pending bit when claim register is read
& ~(((entry == 24'h200004) && memread) << (intClaim-1)); // clear pending bit when claim register is read
flopr #(N) intPendingFlop(HCLK,~HRESETn,nextIntPending,intPending);
// pending array - indexed by priority_lvl x source_ID
@ -212,22 +212,15 @@ module plic (
end
// create threshold mask
// *** I think this commented out version would be nice, but linter complains about circular logic
//assign threshMask[7:1] = {~(7==intThreshold),
// ~(6==intThreshold) & threshMask[7],
// ~(5==intThreshold) & threshMask[6],
// ~(4==intThreshold) & threshMask[5],
// ~(3==intThreshold) & threshMask[4],
// ~(2==intThreshold) & threshMask[3],
// ~(1==intThreshold) & threshMask[2]};
// *** verify that this alternate version does not synthesize to 7 separate comparators
assign threshMask[7:1] = {(7>intThreshold),
(6>intThreshold),
(5>intThreshold),
(4>intThreshold),
(3>intThreshold),
(2>intThreshold),
(1>intThreshold)};
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];
end
// is the max priority > threshold?
// *** would it be any better to first priority encode maxPriority into binary and then ">" with threshold?
assign ExtIntM = |(threshMask & pendingPGrouped);