Add scripts/presyn/ example

scripts/presyn/.gitignore

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+firmware.bin
+firmware.elf
+firmware.hex
+firmware.map
+picorv32_presyn.v
+testbench.vcd
+testbench.vvp

scripts/presyn/Makefile

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+
+TOOLCHAIN_PREFIX = /opt/riscv32ic/bin/riscv32-unknown-elf-
+
+run: testbench.vvp firmware.hex
+	vvp -N testbench.vvp
+
+firmware.hex: firmware.S firmware.c firmware.lds
+	$(TOOLCHAIN_PREFIX)gcc -Os -ffreestanding -nostdlib -o firmware.elf firmware.S firmware.c \
+		 --std=gnu99 -Wl,-Bstatic,-T,firmware.lds,-Map,firmware.map,--strip-debug -lgcc
+	$(TOOLCHAIN_PREFIX)objcopy -O binary firmware.elf firmware.bin
+	python3 ../../firmware/makehex.py firmware.bin 4096 > firmware.hex
+
+picorv32_presyn.v: picorv32_presyn.ys picorv32_regs.txt ../../picorv32.v
+	yosys -v0 picorv32_presyn.ys
+
+testbench.vvp: testbench.v picorv32_presyn.v
+	iverilog -o testbench.vvp testbench.v picorv32_presyn.v
+
+clean:
+	rm -f firmware.bin firmware.elf firmware.hex firmware.map
+	rm -f picorv32_presyn.v testbench.vvp testbench.vcd
+

scripts/presyn/README

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+A simple example for how to use Yosys to "pre-synthesize" PicoRV32 in
+a way that can utilize an external memory module for the register file.
+
+See also:
+https://github.com/cliffordwolf/picorv32/issues/30

scripts/presyn/firmware.S

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+.section .init
+.global main
+
+entry:
+
+/* zero-initialize all registers */
+addi x1, zero, 0
+addi x2, zero, 0
+addi x3, zero, 0
+addi x4, zero, 0
+addi x5, zero, 0
+addi x6, zero, 0
+addi x7, zero, 0
+addi x8, zero, 0
+addi x9, zero, 0
+addi x10, zero, 0
+addi x11, zero, 0
+addi x12, zero, 0
+addi x13, zero, 0
+addi x14, zero, 0
+addi x15, zero, 0
+addi x16, zero, 0
+addi x17, zero, 0
+addi x18, zero, 0
+addi x19, zero, 0
+addi x20, zero, 0
+addi x21, zero, 0
+addi x22, zero, 0
+addi x23, zero, 0
+addi x24, zero, 0
+addi x25, zero, 0
+addi x26, zero, 0
+addi x27, zero, 0
+addi x28, zero, 0
+addi x29, zero, 0
+addi x30, zero, 0
+addi x31, zero, 0
+
+/* set stack pointer */
+lui sp, %hi(16*1024)
+addi sp, sp, %lo(16*1024)
+
+/* call main */
+jal ra, main
+
+/* break */
+ebreak

scripts/presyn/firmware.c

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+void putc(char c)
+{
+	*(volatile char*)0x10000000 = c;
+}
+
+void puts(const char *s)
+{
+	while (*s) putc(*s++);
+}
+
+void *memcpy(void *dest, const void *src, int n)
+{
+	while (n) {
+		n--;
+		((char*)dest)[n] = ((char*)src)[n];
+	}
+	return dest;
+}
+
+void main()
+{
+	char message[] = "$Uryyb+Jbeyq!+Vs+lbh+pna+ernq+guvf+zrffntr+gura$gur+CvpbEI32+PCH"
+			"+frrzf+gb+or+jbexvat+whfg+svar.$$++++++++++++++++GRFG+CNFFRQ!$$";
+	for (int i = 0; message[i]; i++)
+		switch (message[i])
+		{
+		case 'a' ... 'm':
+		case 'A' ... 'M':
+			message[i] += 13;
+			break;
+		case 'n' ... 'z':
+		case 'N' ... 'Z':
+			message[i] -= 13;
+			break;
+		case '$':
+			message[i] = '\n';
+			break;
+		case '+':
+			message[i] = ' ';
+			break;
+		}
+	puts(message);
+}

scripts/presyn/firmware.lds

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+SECTIONS {
+	.memory : {
+		. = 0x000000;
+		*(.init);
+		*(.text);
+		*(*);
+		. = ALIGN(4);
+		end = .;
+	}
+}
+

scripts/presyn/picorv32_presyn.ys

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+read_verilog ../../picorv32.v
+chparam -set COMPRESSED_ISA 1 picorv32
+prep -top picorv32
+memory_bram -rules picorv32_regs.txt
+write_verilog -noattr picorv32_presyn.v

scripts/presyn/picorv32_regs.txt

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+bram picorv32_regs
+  init 0
+  abits 5
+  dbits 32
+  groups 2
+  ports  2 1
+  wrmode 0 1
+  enable 0 1
+  transp 0 0
+  clocks 1 1
+  clkpol 1 1
+endbram
+
+match picorv32_regs
+  make_transp
+endmatch

scripts/presyn/testbench.v

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+module testbench;
+	reg clk = 1;
+	always #5 clk = ~clk;
+
+	reg resetn = 0;
+	always @(posedge clk) resetn <= 1;
+
+	wire        trap;
+	wire        mem_valid;
+	wire        mem_instr;
+	reg         mem_ready;
+	wire [31:0] mem_addr;
+	wire [31:0] mem_wdata;
+	wire [3:0]  mem_wstrb;
+	reg  [31:0] mem_rdata;
+
+	picorv32 UUT (
+		.clk      (clk      ),
+		.resetn   (resetn   ),
+		.trap     (trap     ),
+		.mem_valid(mem_valid),
+		.mem_instr(mem_instr),
+		.mem_ready(mem_ready),
+		.mem_addr (mem_addr ),
+		.mem_wdata(mem_wdata),
+		.mem_wstrb(mem_wstrb),
+		.mem_rdata(mem_rdata)
+	);
+
+	// 4096 32bit words = 16kB memory
+	localparam MEM_SIZE = 4096;
+
+	reg [31:0] memory [0:MEM_SIZE-1];
+	initial $readmemh("firmware.hex", memory);
+
+	always @(posedge clk) begin
+		mem_ready <= 0;
+		mem_rdata <= 'bx;
+
+		if (resetn && mem_valid && !mem_ready) begin
+			mem_ready <= 1;
+			if (mem_wstrb) begin
+				if (mem_addr == 32'h1000_0000) begin
+					$write("%c", mem_wdata[7:0]);
+					$fflush;
+				end else begin
+					if (mem_wstrb[0]) memory[mem_addr >> 2][ 7: 0] <= mem_wdata[ 7: 0];
+					if (mem_wstrb[1]) memory[mem_addr >> 2][15: 8] <= mem_wdata[15: 8];
+					if (mem_wstrb[2]) memory[mem_addr >> 2][23:16] <= mem_wdata[23:16];
+					if (mem_wstrb[3]) memory[mem_addr >> 2][31:24] <= mem_wdata[31:24];
+				end
+			end else begin
+				mem_rdata <= memory[mem_addr >> 2];
+			end
+		end
+
+		if (resetn && trap) begin
+			$display("TRAP.");
+			$finish;
+		end
+	end
+
+	initial begin
+		$dumpfile("testbench.vcd");
+		$dumpvars(0, testbench);
+	end
+endmodule
+
+module picorv32_regs (
+	input [4:0] A1ADDR, A2ADDR, B1ADDR,
+	output reg [31:0] A1DATA, A2DATA,
+	input [31:0] B1DATA,
+	input B1EN, CLK1
+);
+	reg [31:0] memory [0:31];
+	always @(posedge CLK1) begin
+		A1DATA <= memory[A1ADDR];
+		A2DATA <= memory[A2ADDR];
+		if (B1EN) memory[B1ADDR] <= B1DATA;
+	end
+endmodule