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bit-string-accelerator

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bit-string-accelerator / rtl /bit_accelerator.sv
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// Bit-string accelerator: one GET/TEST/SET/CLEAR/TOGGLE per operation on a
// 64-bit-word memory. See docs/verification.md for the interface contract.
//
// effective_bit = (base_address << 3) + bit_offset (mod 2^64)
// mem_addr = (effective_bit >> 6) << 3 (8-byte aligned)
// bit index = effective_bit[5:0] (LSB-first)
//
// result_valid is a one-cycle pulse; error and result_bit are valid in that
// same cycle. On error, result_bit holds its previous value.
module bit_accelerator #(
parameter int ADDR_W=64,
parameter int WORD_W=64
)(
input logic clk,input logic reset,
input logic op_valid, output logic op_ready,
input logic [ADDR_W-1:0] base_address,
input logic [63:0] bit_offset,
input logic [2:0] operation,
output logic result_valid, output logic result_bit, output logic error,
output logic mem_valid, output logic mem_write,
output logic [ADDR_W-1:0] mem_addr,
output logic [WORD_W-1:0] mem_wdata,
output logic [WORD_W/8-1:0] mem_wstrb,
input logic mem_ready, input logic mem_rvalid,
input logic [WORD_W-1:0] mem_rdata, input logic mem_fault
);
localparam logic [2:0] OP_GET=3'b000, OP_TEST=3'b001, OP_SET=3'b010,
OP_CLEAR=3'b011, OP_TOGGLE=3'b100;
typedef enum logic [2:0] {IDLE,READ_REQ,READ_WAIT,WRITE_REQ,WRITE_WAIT,RESP} state_t;
state_t state;
logic [ADDR_W-1:0] req_addr;
logic [63:0] eff_bit;
logic [5:0] bit_idx_q;
logic err_q; // error latched during the operation, reported with result_valid
logic [2:0] op_q;
logic old_bit_q;
logic [WORD_W-1:0] new_word_q;
logic [WORD_W-1:0] shifted_one;
assign op_ready = (state == IDLE) && !reset;
assign mem_valid = (state == READ_REQ || state == WRITE_REQ);
assign mem_write = (state == WRITE_REQ);
assign mem_addr = req_addr;
assign mem_wdata = new_word_q;
assign mem_wstrb = {WORD_W/8{1'b1}};
assign shifted_one = ({{(WORD_W-1){1'b0}},1'b1} << bit_idx_q);
assign eff_bit = (64'(base_address) << 3) + bit_offset;
always_ff @(posedge clk) begin
if (reset) begin
state <= IDLE; result_valid <= 1'b0; result_bit <= 1'b0; error <= 1'b0;
req_addr <= '0; bit_idx_q <= '0; err_q <= 1'b0;
op_q <= OP_GET; old_bit_q <= 1'b0; new_word_q <= '0;
end else begin
result_valid <= 1'b0; error <= 1'b0;
case (state)
IDLE: if (op_valid) begin
op_q <= operation;
err_q <= 1'b0;
bit_idx_q <= eff_bit[5:0];
req_addr <= ADDR_W'((eff_bit >> 6) << 3);
state <= READ_REQ;
end
READ_REQ: if (mem_ready) state <= READ_WAIT;
READ_WAIT: if (mem_fault) begin err_q <= 1'b1; state <= RESP; end
else if (mem_rvalid) begin
old_bit_q <= mem_rdata[bit_idx_q];
case (op_q)
OP_GET, OP_TEST: state <= RESP;
OP_SET: begin new_word_q <= mem_rdata | shifted_one; state <= WRITE_REQ; end
OP_CLEAR: begin new_word_q <= mem_rdata & ~shifted_one; state <= WRITE_REQ; end
OP_TOGGLE: begin new_word_q <= mem_rdata ^ shifted_one; state <= WRITE_REQ; end
default: begin err_q <= 1'b1; state <= RESP; end
endcase
end
WRITE_REQ: if (mem_ready) state <= WRITE_WAIT;
WRITE_WAIT: begin
if (mem_fault) err_q <= 1'b1;
state <= RESP;
end
RESP: begin
result_valid <= 1'b1;
error <= err_q;
if (!err_q) begin
case (op_q)
OP_GET, OP_TEST: result_bit <= old_bit_q;
OP_SET: result_bit <= 1'b1;
OP_CLEAR: result_bit <= 1'b0;
OP_TOGGLE: result_bit <= ~old_bit_q;
default: result_bit <= 1'b0;
endcase
end
state <= IDLE;
end
default: state <= IDLE;
endcase
end
end
endmodule