| 1 | `include "ram.v" |
| 2 | `include "prescaler.v" |
| 3 | `include "single_trigger.v" |
| 4 | `include "multiple_trigger.v" |
| 5 | |
| 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 |
| 13 | |
| 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] |
| 22 | |
| 23 | function [7:0] reverse (input [7:0] forward); |
| 24 | integer i; |
| 25 | for (i = 0; i < 8; i = i + 1) |
| 26 | reverse[7-i] = forward[i]; |
| 27 | endfunction |
| 28 | |
| 29 | function [7:0] select (input condition, input [7:0] word); |
| 30 | integer i; |
| 31 | select = condition ? word : 8'b00000000; |
| 32 | endfunction |
| 33 | |
| 34 | // This is a thirty-two bit accumulator machine identical to the Manchester SSEM. |
| 35 | |
| 36 | module PROCESSOR (input clk, output [23:0] led, output [3:0] indicators, input [15:0] buttons); |
| 37 | |
| 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 |
| 41 | |
| 42 | wire clock; |
| 43 | |
| 44 | PRESCALER #(.BITS(2)) scal0 (.clk(clk), .out(clock)); |
| 45 | |
| 46 | // Handle running |
| 47 | |
| 48 | reg running = 0; |
| 49 | |
| 50 | always @ (posedge `RUN_BUTTON) begin |
| 51 | |
| 52 | running <= !running; |
| 53 | |
| 54 | end |
| 55 | |
| 56 | // Generate running clock |
| 57 | |
| 58 | wire running_counter; |
| 59 | |
| 60 | PRESCALER #(.BITS(6)) scal1 (.clk(clock), .out(running_counter)); |
| 61 | |
| 62 | wire running_clk = running & running_counter; |
| 63 | |
| 64 | // Handle execution |
| 65 | |
| 66 | wire [4:0] execute_trigger; |
| 67 | |
| 68 | MULTIPLE_TRIGGER #(.BITS(4)) trig0 (.clk(clock), .trigger_in(!running & `EXECUTE_BUTTON), .trigger_out(execute_trigger)); |
| 69 | |
| 70 | wire [4:0] running_trigger; |
| 71 | |
| 72 | MULTIPLE_TRIGGER #(.BITS(5)) trig1 (.clk(clock), .trigger_in(running_clk), .trigger_out(running_trigger)); |
| 73 | |
| 74 | wire [4:0] execute = execute_trigger | running_trigger; |
| 75 | |
| 76 | // Handle halt |
| 77 | |
| 78 | reg halt = 0; |
| 79 | |
| 80 | wire newHalt = execute[3] & (inst == `INST_HALT) ? 1 : |
| 81 | !running ? 0 : |
| 82 | halt; |
| 83 | |
| 84 | always @ (posedge clock) begin |
| 85 | |
| 86 | halt <= newHalt; |
| 87 | |
| 88 | end |
| 89 | |
| 90 | // Handle program space |
| 91 | |
| 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. |
| 94 | |
| 95 | wire [31:0] pOut; |
| 96 | |
| 97 | wire [7:0] reverseButtons = reverse(buttons[7:0]); |
| 98 | |
| 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; |
| 100 | |
| 101 | wire write_trigger; |
| 102 | |
| 103 | wire program_buttons = (buttons[0] | buttons[1] | buttons[2] | buttons[3] | buttons[4] | buttons[5] | buttons[6] | buttons[7]); |
| 104 | |
| 105 | SINGLE_TRIGGER trig2 (.clk(clk), .trigger_in(program_buttons), .trigger_out(write_trigger)); |
| 106 | |
| 107 | wire [4:0] address = (execute[2] | execute[3]) ? addr : pc; |
| 108 | |
| 109 | wire [31:0] pIn = execute[2] & (inst == `INST_STO) ? accum : buffer; |
| 110 | |
| 111 | wire write_enable = (!running & write_trigger) | (execute[2] & (inst == `INST_STO)); |
| 112 | |
| 113 | RAM #(.DATA_BITS(32),.ADDRESS_BITS(5)) programMemory (.clk(clk), .write(write_enable), .addr(address), .in_data(pIn), .out_data(pOut)); |
| 114 | |
| 115 | // Handle page |
| 116 | |
| 117 | reg [1:0] page = 0; |
| 118 | |
| 119 | wire page_prev_trigger; |
| 120 | wire page_next_trigger; |
| 121 | |
| 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)); |
| 124 | |
| 125 | wire [1:0] newPage = page_prev_trigger ? (page + 2'b11) : page_next_trigger ? (page + 2'b01) : page; |
| 126 | |
| 127 | always @ (posedge clock) begin |
| 128 | |
| 129 | page <= newPage; |
| 130 | |
| 131 | end |
| 132 | |
| 133 | // Handle PC |
| 134 | |
| 135 | reg [4:0] pc = 0; |
| 136 | |
| 137 | wire [4:0] nextPc = pc + 5'b00001; |
| 138 | wire [4:0] prevPc = pc + 5'b11111; |
| 139 | |
| 140 | wire pc_prev_trigger; |
| 141 | wire pc_next_trigger; |
| 142 | wire pc_zero_trigger; |
| 143 | |
| 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)); |
| 147 | |
| 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 : |
| 155 | pc; |
| 156 | |
| 157 | always @ (posedge clock) begin |
| 158 | |
| 159 | pc <= newPc; |
| 160 | |
| 161 | end |
| 162 | |
| 163 | // Handle instruction |
| 164 | |
| 165 | reg [2:0] inst = 0; |
| 166 | reg [4:0] addr = 0; |
| 167 | |
| 168 | wire [2:0] newInst = execute[1] ? pOut[15:13] : |
| 169 | inst; |
| 170 | |
| 171 | wire [4:0] newAddr = execute[1] ? pOut[4:0] : |
| 172 | addr; |
| 173 | |
| 174 | always @ (posedge clock) begin |
| 175 | |
| 176 | inst <= newInst; |
| 177 | |
| 178 | addr <= newAddr; |
| 179 | |
| 180 | end |
| 181 | |
| 182 | // Handle accumulator |
| 183 | |
| 184 | reg [31:0] accum = 0; |
| 185 | |
| 186 | wire accum_zero_trigger; |
| 187 | |
| 188 | SINGLE_TRIGGER trig6 (.clk(clock), .trigger_in(`ACCUM_CLR_BUTTON), .trigger_out(accum_zero_trigger)); |
| 189 | |
| 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 : |
| 193 | accum; |
| 194 | |
| 195 | always @ (posedge clock) begin |
| 196 | |
| 197 | accum <= newAccum; |
| 198 | |
| 199 | end |
| 200 | |
| 201 | // Assign the outputs |
| 202 | |
| 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] : |
| 206 | pOut[31:24]; |
| 207 | |
| 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] : |
| 211 | accum[31:24]; |
| 212 | |
| 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}; |
| 217 | |
| 218 | endmodule |
| 219 | |