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Improvements in PCPI MUL core

This commit is contained in:
Clifford Wolf 2015-06-30 16:51:26 +02:00
parent 9d809eb0d9
commit 4a9fda0737
1 changed files with 15 additions and 10 deletions
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25
picorv32.v
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@ -1019,8 +1019,8 @@ endmodule
***************************************************************/ ***************************************************************/
module picorv32_pcpi_mul #( module picorv32_pcpi_mul #(
// increasing this parameter increases performance and core size parameter STEPS_AT_ONCE = 1,
parameter STEPS_AT_ONCE = 1 parameter CARRY_CHAIN = 4
) ( ) (
input clk, resetn, input clk, resetn,
@ -1062,11 +1062,12 @@ module picorv32_pcpi_mul #(
end end
reg [63:0] rs1, rs2, rd, rdx; reg [63:0] rs1, rs2, rd, rdx;
reg [63:0] next_rs1, next_rs2, next_rd, next_rdx, next_rdt; reg [63:0] next_rs1, next_rs2, this_rs2;
reg [63:0] next_rd, next_rdx, next_rdt;
reg [6:0] mul_counter; reg [6:0] mul_counter;
reg mul_waiting; reg mul_waiting;
reg mul_finish; reg mul_finish;
integer i; integer i, j;
// carry save accumulator // carry save accumulator
always @* begin always @* begin
@ -1076,14 +1077,18 @@ module picorv32_pcpi_mul #(
next_rs2 = rs2; next_rs2 = rs2;
for (i = 0; i < STEPS_AT_ONCE; i=i+1) begin for (i = 0; i < STEPS_AT_ONCE; i=i+1) begin
if (next_rs1[0]) begin this_rs2 = next_rs1[0] ? next_rs2 : 0;
next_rdt = (next_rd ^ next_rdx) ^ next_rs2; if (CARRY_CHAIN == 0) begin
next_rdx = ((next_rd & next_rdx) | (next_rd & next_rs2) | (next_rdx & next_rs2)) << 1; next_rdt = next_rd ^ next_rdx ^ this_rs2;
next_rdx = ((next_rd & next_rdx) | (next_rd & this_rs2) | (next_rdx & this_rs2)) << 1;
next_rd = next_rdt;
end else begin end else begin
next_rdt = next_rd ^ next_rdx; next_rdt = 0;
next_rdx = (next_rd & next_rdx) << 1; for (j = 0; j < 64; j = j + CARRY_CHAIN)
{next_rdt[j+CARRY_CHAIN-1], next_rd[j +: CARRY_CHAIN]} =
next_rd[j +: CARRY_CHAIN] + next_rdx[j +: CARRY_CHAIN] + this_rs2[j +: CARRY_CHAIN];
next_rdx = next_rdt << 1;
end end
next_rd = next_rdt;
next_rs1 = next_rs1 >> 1; next_rs1 = next_rs1 >> 1;
next_rs2 = next_rs2 << 1; next_rs2 = next_rs2 << 1;
end end