From 4a9fda07373feb53c112d9bce2591808b54a5004 Mon Sep 17 00:00:00 2001 From: Clifford Wolf Date: Tue, 30 Jun 2015 16:51:26 +0200 Subject: Improvements in PCPI MUL core --- picorv32.v | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) (limited to 'picorv32.v') diff --git a/picorv32.v b/picorv32.v index 8a02494..bda9da3 100644 --- a/picorv32.v +++ b/picorv32.v @@ -1019,8 +1019,8 @@ endmodule ***************************************************************/ 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, @@ -1062,11 +1062,12 @@ module picorv32_pcpi_mul #( end 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 mul_waiting; reg mul_finish; - integer i; + integer i, j; // carry save accumulator always @* begin @@ -1076,14 +1077,18 @@ module picorv32_pcpi_mul #( next_rs2 = rs2; for (i = 0; i < STEPS_AT_ONCE; i=i+1) begin - if (next_rs1[0]) begin - next_rdt = (next_rd ^ next_rdx) ^ next_rs2; - next_rdx = ((next_rd & next_rdx) | (next_rd & next_rs2) | (next_rdx & next_rs2)) << 1; + this_rs2 = next_rs1[0] ? next_rs2 : 0; + if (CARRY_CHAIN == 0) begin + 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 - next_rdt = next_rd ^ next_rdx; - next_rdx = (next_rd & next_rdx) << 1; + next_rdt = 0; + 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 - next_rd = next_rdt; next_rs1 = next_rs1 >> 1; next_rs2 = next_rs2 << 1; end -- cgit