3 `include "single_trigger.v"
4 `include "multiple_trigger.v"
6 `define INST_JMP 3'b000
7 `define INST_JPR 3'b001
8 `define INST_LDN 3'b010
9 `define INST_STO 3'b011
10 `define INST_SUB 3'b100
11 `define INST_SKN 3'b110
12 `define INST_HALT 3'b111
14 `define PC_INC_BUTTON buttons[8]
15 `define PC_DEC_BUTTON buttons[9]
16 `define PAGE_INC_BUTTON buttons[10]
17 `define PAGE_DEC_BUTTON buttons[11]
18 `define PC_CLR_BUTTON buttons[12]
19 `define ACCUM_CLR_BUTTON buttons[13]
20 `define RUN_BUTTON buttons[14]
21 `define EXECUTE_BUTTON buttons[15]
23 function [7:0] reverse (input [7:0] forward);
25 for (i = 0; i < 8; i = i + 1)
26 reverse[7-i] = forward[i];
29 function [7:0] select (input condition, input [7:0] word);
31 select = condition ? word : 8'b00000000;
34 // This is a thirty-two bit accumulator machine identical to the Manchester SSEM.
36 module PROCESSOR (input clk, output [23:0] led, output [3:0] indicators, input [15:0] buttons);
38 // We use two clocks - the main one for all the registers and one for the RAM
39 // The RAM clock is twice as fast as the register one to simulate the effect
40 // of flow through RAM which is not supported on the FPGA
44 PRESCALER #(.BITS(2)) scal0 (.clk(clk), .out(clock));
50 always @ (posedge `RUN_BUTTON) begin
56 // Generate running clock
60 PRESCALER #(.BITS(6)) scal1 (.clk(clock), .out(running_counter));
62 wire running_clk = running & running_counter;
66 wire [4:0] execute_trigger;
68 MULTIPLE_TRIGGER #(.BITS(4)) trig0 (.clk(clock), .trigger_in(!running & `EXECUTE_BUTTON), .trigger_out(execute_trigger));
70 wire [4:0] running_trigger;
72 MULTIPLE_TRIGGER #(.BITS(5)) trig1 (.clk(clock), .trigger_in(running_clk), .trigger_out(running_trigger));
74 wire [4:0] execute = execute_trigger | running_trigger;
80 wire newHalt = execute[3] & (inst == `INST_HALT) ? 1 :
84 always @ (posedge clock) begin
90 // Handle program space
92 // Note that this uses the RAM clock even for the buffer update. Failing to do results in two buffer updates
93 // which leaves the RAM contents unchanged.
97 wire [7:0] reverseButtons = reverse(buttons[7:0]);
99 wire [31:0] buffer = { select(page == 2'b11, reverseButtons), select(page == 2'b10, reverseButtons), select(page == 2'b01, reverseButtons), select(page == 2'b00, reverseButtons) } ^ pOut;
103 wire program_buttons = (buttons[0] | buttons[1] | buttons[2] | buttons[3] | buttons[4] | buttons[5] | buttons[6] | buttons[7]);
105 SINGLE_TRIGGER trig2 (.clk(clk), .trigger_in(program_buttons), .trigger_out(write_trigger));
107 wire [4:0] address = (execute[2] | execute[3]) ? addr : pc;
109 wire [31:0] pIn = execute[2] & (inst == `INST_STO) ? accum : buffer;
111 wire write_enable = (!running & write_trigger) | (execute[2] & (inst == `INST_STO));
113 RAM #(.DATA_BITS(32),.ADDRESS_BITS(5)) programMemory (.clk(clk), .write(write_enable), .addr(address), .in_data(pIn), .out_data(pOut));
119 wire page_prev_trigger;
120 wire page_next_trigger;
122 SINGLE_TRIGGER trig7 (.clk(clock), .trigger_in(`PAGE_DEC_BUTTON), .trigger_out(page_prev_trigger));
123 SINGLE_TRIGGER trig8 (.clk(clock), .trigger_in(`PAGE_INC_BUTTON), .trigger_out(page_next_trigger));
125 wire [1:0] newPage = page_prev_trigger ? (page + 2'b11) : page_next_trigger ? (page + 2'b01) : page;
127 always @ (posedge clock) begin
137 wire [4:0] nextPc = pc + 5'b00001;
138 wire [4:0] prevPc = pc + 5'b11111;
140 wire pc_prev_trigger;
141 wire pc_next_trigger;
142 wire pc_zero_trigger;
144 SINGLE_TRIGGER trig3 (.clk(clock), .trigger_in(`PC_INC_BUTTON), .trigger_out(pc_next_trigger));
145 SINGLE_TRIGGER trig4 (.clk(clock), .trigger_in(`PC_DEC_BUTTON), .trigger_out(pc_prev_trigger));
146 SINGLE_TRIGGER trig5 (.clk(clock), .trigger_in(`PC_CLR_BUTTON), .trigger_out(pc_zero_trigger));
148 wire [4:0] newPc = execute[3] & (inst == `INST_JMP) ? pOut[4:0] :
149 execute[3] & (inst == `INST_JPR) ? pc + pOut[4:0] :
150 execute[3] & (inst == `INST_SKN) & (accum[31] == 1) ? nextPc :
151 !halt & execute[0] ? nextPc :
152 !running & pc_zero_trigger ? 5'b00000 :
153 !running & pc_next_trigger ? nextPc :
154 !running & pc_prev_trigger ? prevPc :
157 always @ (posedge clock) begin
163 // Handle instruction
168 wire [2:0] newInst = execute[1] ? pOut[15:13] :
171 wire [4:0] newAddr = execute[1] ? pOut[4:0] :
174 always @ (posedge clock) begin
182 // Handle accumulator
184 reg [31:0] accum = 0;
186 wire accum_zero_trigger;
188 SINGLE_TRIGGER trig6 (.clk(clock), .trigger_in(`ACCUM_CLR_BUTTON), .trigger_out(accum_zero_trigger));
190 wire [31:0] newAccum = execute[2] & (inst == `INST_LDN) ? 0 - pOut :
191 execute[2] & (inst == `INST_SUB) ? accum - pOut :
192 !running & accum_zero_trigger ? 0 :
195 always @ (posedge clock) begin
201 // Assign the outputs
203 wire [7:0] selectedOut = (page == 2'b00) ? pOut[7:0] :
204 (page == 2'b01) ? pOut[15:8] :
205 (page == 2'b10) ? pOut[23:16] :
208 wire [7:0] selectedAccum = (page == 2'b00) ? accum[7:0] :
209 (page == 2'b01) ? accum[15:8] :
210 (page == 2'b10) ? accum[23:16] :
213 assign led[7:0] = reverse(selectedOut);
214 assign led[15:8] = reverse(selectedAccum);
215 assign led[23:16] = {page, 1'b0, pc};
216 assign indicators = {1'b0, (!running & `EXECUTE_BUTTON) | running_clk, halt, running & !halt};