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|
`include "util.svh"
module top
#( ADDR_BITS = 14
, DATA_BITS = 12
)
( input bit clk // verilator public
, input bit reset_n // verilator public
);
bit reset = 0;
bit have_reset = 0;
always_ff @(posedge clk) if (reset) have_reset <= 1;
assign reset = !reset_n || !have_reset;
bit mem_ready; `define mem_ready `past(mem_ready)
bit mem_valid;
bit mem_write;
bit [ADDR_BITS-1:0] mem_address;
bit [DATA_BITS-1:0] mem_write_data;
bit mem_read_valid; `define mem_read_valid `past(mem_read_valid)
bit [DATA_BITS-1:0] mem_read_data; `define mem_read_data `past(mem_read_data)
mem
#( .ADDR_BITS(ADDR_BITS)
, .DATA_BITS(DATA_BITS)
, .INIT_FILE("mem/mem.hex")
)
memory
( .clk(clk)
, .reset(reset)
, .ready(mem_ready)
, .valid(mem_valid)
, .address(mem_address)
, .write(mem_write)
, .write_data(mem_write_data)
, .read_valid(mem_read_valid)
, .read_data(mem_read_data)
);
bit rx_ready;
bit rx_valid;
bit [7:0] rx_data;
bit tx_ready;
bit tx_valid;
bit [7:0] tx_data;
jtag_uart
#( .INSTANCE(0)
) uart0
( .clk(clk)
, .reset(reset)
, .rx_ready(rx_ready)
, .rx_valid(rx_valid) `define rx_valid `past(rx_valid)
, .rx_data(rx_data) `define rx_data `past(rx_data)
, .tx_ready(tx_ready) `define tx_ready `past(tx_ready)
, .tx_valid(tx_valid)
, .tx_data(tx_data)
);
bit [DATA_BITS-1:0] pc;
bit [3:0] opcode;
bit [7:0] operand;
bit [DATA_BITS-1:0] acc;
bit [DATA_BITS-1:0] idx;
bit [ADDR_BITS-1:0] address;
bit [DATA_BITS-1:0] sign_extended_operand;
enum
{ FETCH
, DECODE
, INDIRECT
, INDIRECTED
, AGEN
, MEMORY
, HALT
} state;
always_ff @(posedge clk) begin
if (reset) begin
mem_valid = 0;
rx_ready = 0;
tx_valid = 0;
tx_data = 0;
pc = 0;
acc = 0;
idx = 0;
state = state.first;
end else begin
`ifdef DEBUG $display("s=%0d pc=%x (acc=%x idx=%x) (mem %b:%x)", state, pc, acc, idx, `mem_read_valid, `mem_read_data); `endif
if (`tx_ready) tx_valid = 0;
case (state)
FETCH: begin
`ifdef DEBUG $display("\tfetch"); `endif
mem_valid = 1;
mem_address = {2'b0, pc};
mem_write = 0;
if (`mem_ready) begin
state = DECODE;
++pc;
end
end
DECODE: begin
mem_valid = 0;
mem_write = 0;
if (`mem_read_valid) begin
state = FETCH;
{opcode, operand} = `mem_read_data;
sign_extended_operand = {{(DATA_BITS-8){operand[7]}}, operand};
`ifdef DEBUG $display("\tdecode %x:%x", opcode, operand); `endif
case (opcode)
'h0: acc = sign_extended_operand;
'h1, 'h2: begin
address = {7'b0, operand[6:0]};
state = operand[7] ? INDIRECT : AGEN;
end
'h3: if (acc != sign_extended_operand) ++pc;
'h4: pc = pc + sign_extended_operand;
'h5: begin
mem_write_data = acc % 10 + 'h30;
acc = acc / 10;
address = {7'b0, operand[6:0]};
state = operand[7] ? INDIRECT : AGEN;
end
'hf: begin
if (operand[0]) ++acc;
if (operand[1]) --acc;
if (operand[2]) ++idx;
if (operand[3]) --idx;
if (operand[4]) {idx, acc} = {acc, idx};
if (operand[5]) idx = acc;
if (operand[6]) state = MEMORY;
if (operand[7]) state = HALT;
end
endcase
end
end
INDIRECT: begin
mem_valid = 1;
mem_write = 0;
mem_address = address;
state = `mem_ready ? INDIRECTED : INDIRECT;
end
INDIRECTED: begin
if (`mem_ready) begin
mem_valid = 0;
mem_write = 0;
end
if (`mem_read_valid) begin
address = `mem_read_data;
state = AGEN;
end
end
AGEN: begin
mem_valid = 0;
mem_write = 0;
state = FETCH;
`ifdef DEBUG $display("\tagen"); `endif
case (opcode)
'h1: begin
mem_valid = 1;
mem_address = address + idx;
state = `mem_ready ? MEMORY : AGEN;
end
'h2: begin
mem_valid = 1;
mem_address = address + idx;
mem_write = 1;
mem_write_data = acc;
state = `mem_ready ? FETCH : AGEN;
end
'h5: begin
mem_valid = 1;
mem_address = address + idx;
mem_write = 1;
state = `mem_ready ? FETCH : AGEN;
end
endcase
end
MEMORY: begin
if (`mem_ready) begin
mem_valid = 0;
mem_write = 0;
end
state = FETCH;
`ifdef DEBUG $display("\tstall"); `endif
case (opcode)
'h1: begin
if (`mem_read_valid) begin
acc = acc + `mem_read_data;
end else begin
state = MEMORY;
end
end
'hf: begin
if (operand[6]) begin
if (tx_valid) begin
state = MEMORY;
end else begin
tx_valid = 1;
tx_data = acc[7:0];
end
end
end
endcase
end
HALT: begin
$display("Reached halt state.");
$finish;
end
endcase
`ifdef DEBUG if (mem_valid) $display("\tmem addr=%x w=%b", mem_address, mem_write); `endif
end
end
endmodule
|
