sw: Add bootrom

sw/bootrom/.gitignore

@@ -0,0 +1,4 @@
+*.bin
+*.elf
+*.hex
+*.vhex

sw/bootrom/boot.ld

@@ -0,0 +1,45 @@
+__heap_size  = 0x80;
+__stack_size = 0x80;
+
+MEMORY
+{
+	ROM (rwx) : ORIGIN = 0x00000000, LENGTH = 0x100
+	RAM (rwx) : ORIGIN = 0x40000000, LENGTH = 0x400
+}
+SECTIONS
+{
+	.text :
+	{
+		*(.boot)
+		*(.text)
+		*(.text)
+		*(.rodata*)
+	} > ROM
+	.data :
+	{
+		*(.sbss)
+		*(.data)
+		*(.bss)
+		*(.rela*)
+		*(COMMON)
+	} > RAM
+
+	.heap :
+	{
+		. = ALIGN(4);
+		PROVIDE ( end = . );
+		_sheap = .;
+		. = . + __heap_size;
+		. = ALIGN(4);
+		_eheap = .;
+	} >RAM
+
+	.stack :
+	{
+		. = ALIGN(4);
+		_estack = .;
+		. = . + __stack_size;
+		. = ALIGN(4);
+		_sstack = .;
+	} >RAM
+}

sw/bootrom/build.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+set -e
+
+riscv64-elf-gcc -mabi=ilp32 -march=rv32i -nostdlib -nostartfiles -ffreestanding -T boot.ld -Os -o bootrom.elf main.c
+#riscv64-elf-objdump -D bootrom.elf
+riscv64-elf-objcopy -O binary bootrom.elf bootrom.bin
+od --endian=little -vtx4 -An -w4 bootrom.bin | tr -d ' ' > bootrom.vhex
+r2 -A -c 'pdf @ sym._start' -q bootrom.elf

sw/bootrom/main.c

@@ -0,0 +1,87 @@
+#include <inttypes.h>
+
+#define UART0_BASE 0x81000000
+#define UART0_SR (*((volatile uint32_t *) (UART0_BASE + 0x00)))
+#define UART0_DR (*((volatile uint32_t *) (UART0_BASE + 0x04)))
+
+#define UART0_SR_RX_DATA_EMPTY (1 << 0)
+#define UART0_SR_TX_FULL (1 << 1)
+
+/*
+// Set up stack pointer
+asm("_start:\
+	xor sp, sp, sp;\
+	lui sp, 0x80100;\
+	j main;\
+");
+*/
+
+__attribute__((noreturn)) void _start() {
+	uint8_t state = 0;
+	uint8_t c;
+	uint8_t opcode;
+	uint8_t *ptr;
+	uint32_t length;
+
+	/*while (1) {
+		while (UART0_SR & UART0_SR_RX_DATA_EMPTY);
+		c = UART0_DR;
+		while (UART0_SR & UART0_SR_TX_FULL);
+		UART0_DR = c;
+	}*/
+
+	while (1) {
+		while (UART0_SR & UART0_SR_RX_DATA_EMPTY);
+		c = UART0_DR;
+		state++;
+		switch (state) {
+			case 1: // Opcode
+				opcode = c;
+				ptr = 0;
+				length = 0;
+				if (c == 0) // NOP
+					state = 0;
+				break;
+			case 2: // Address
+			case 3:
+			case 4:
+			case 5:
+				ptr = (uint8_t*)(((uint32_t)ptr << 8) | c);
+				if (state != 5)
+					break;
+				if (opcode == 3) { // Jump
+					//((void (*)()) ptr)();
+					asm("jalr %0" : : "r"(ptr)); // Not sure why, but the jump above causes GCC to save variables to the stack at the beginning of this function
+					__builtin_unreachable();
+				}
+				break;
+			case 6: // Length
+			case 7:
+			case 8:
+			case 9:
+				length = (length << 8) | c;
+				if (state != 9)
+					break;
+				if (opcode == 2) { // Read
+					for (; length > 0; length--) {
+						while (UART0_SR & UART0_SR_TX_FULL);
+						UART0_DR = *(ptr);
+						ptr++;
+					}
+					state = 0;
+				}
+				break;
+			case 10: // Write byte by byte
+				*(ptr++) = c;
+				if (--length == 0) {
+					state = 0;
+				} else {
+					state--; // Stay in this state
+				}
+				break;
+			default:
+				break;
+		}
+	}
+	__builtin_unreachable();
+}