fernly: Add two-stage bootloader and get basics working

The romulator only emulates 64k of SPI ROM.  That's not enough for anything
interesting.

Add a second-stage bootloader to send data to Fernvale over serial.  This
will allow us to work around needing code relocations, and allow for much
larger binaries.

fernly-loader.c

@@ -0,0 +1,128 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+int fernvale_reset(void) {
+	int fd;
+	uint8_t b;
+
+	fd = open("/sys/class/gpio/gpio17/value", O_WRONLY);
+	b = '0';
+	write(fd, &b, 1);
+	close(fd);
+	
+	usleep(250000);
+
+	fd = open("/sys/class/gpio/gpio17/value", O_WRONLY);
+	b = '1';
+	write(fd, &b, 1);
+	close(fd);
+
+	return 0;
+}
+
+int fernvale_banner(int fd) {
+	uint8_t b;
+
+	while (-1 != read(fd, &b, 1)) {
+		if (b == '>')
+			return 0;
+		printf("%c", b);
+		fflush(stdout);
+		if (b == '\r')
+			printf("\t");
+	}
+	return -1;
+}
+
+int fernvale_print_line(int fd) {
+	uint8_t b;
+
+	while (-1 != read(fd, &b, 1)) {
+		printf("%c", b);
+		if (b == '\n')
+			return 0;
+	}
+	return -1;
+}
+
+int main(int argc, char **argv) {
+	int serfd, binfd;
+	struct stat stats;
+	int i;
+	
+	if (argc != 2) {
+		printf("Usage: %s firmware.bin\n", argv[0]);
+		exit(1);
+	}
+
+	serfd = open("/dev/ttymxc2", O_RDWR);
+	if (-1 == serfd) {
+		perror("Unable to open serial port");
+		exit(1);
+	}
+
+	binfd = open(argv[1], O_RDONLY);
+	if (-1 == binfd) {
+		perror("Unable to open firmware file");
+		exit(1);
+	}
+
+	if (-1 == fstat(binfd, &stats)) {
+		perror("Unable to get file stats");
+		exit(1);
+	}
+
+	printf("Resetting Fernvale... ");
+	fflush(stdout);
+	fernvale_reset();
+	printf("Ok.\n");
+
+	printf("Waiting for banner... ");
+	fflush(stdout);
+	fernvale_banner(serfd);
+	printf("Ok.\n");
+
+	printf("Writing %d bytes...", (int)stats.st_size);
+	{
+		uint8_t b;
+
+		b = stats.st_size & 0xff;
+		write(serfd, &b, 1);
+
+		b = stats.st_size >> 8 & 0xff;
+		write(serfd, &b, 1);
+
+		b = stats.st_size >> 16 & 0xff;
+		write(serfd, &b, 1);
+
+		b = stats.st_size >> 24 & 0xff;
+		write(serfd, &b, 1);
+	}
+
+	for (i = 0; i < stats.st_size; i++) {
+		uint8_t b;
+		if (-1 == read(binfd, &b, 1)) {
+			perror("Error while reading binary");
+			exit(1);
+		}
+		if (-1 == write(serfd, &b, 1)) {
+			perror("Error while writing binary to serial port");
+			exit(1);
+		}
+	}
+
+	printf(" Done.\n");
+
+	printf("Result: ");
+	fernvale_print_line(serfd);
+
+	close(serfd);
+	close(binfd);
+	return execl("/usr/bin/screen", "screen", "/dev/ttymxc2", "115200", NULL);
+	return 0;
+}

loader.S

@@ -0,0 +1,119 @@
+.text
+
+.global _start
+_start:
+	ldr	r0, =0x7000cffc // stack_start
+	mov	sp, r0
+	mov	r2, #0xffffffff
+	ldr	r1, =0x7000c000 // stack_end
+
+clear_stack:
+	cmp	r1, r0
+	str	r2, [r0]
+	sub	r0, r0, #4
+	bcc	clear_stack
+
+	bl	wdt_disable
+
+	adr	r0, welcome_banner
+	bl	uart_puts
+
+load_program:
+	bl	uart_getc
+	mov	r5, r0
+	lsls	r5, r5, #0
+	mov	r4, r5
+
+	bl	uart_getc
+	mov	r5, r0
+	lsls	r5, r5, #8
+	orr	r4, r5
+
+	bl	uart_getc
+	mov	r5, r0
+	lsls	r5, r5, #16
+	orr	r4, r5
+
+	bl	uart_getc
+	mov	r5, r0
+	lsls	r5, r5, #24
+	orr	r4, r5
+
+# r4 now contains the number of bytes to load.
+# r5 contains the current offset to write to.
+# Load bytes from the serial port into RAM.
+	mov	r5, #0
+loader_loop:
+	bl	uart_getc
+	strb	r0, [r5], #1
+	sub	r4, #1
+	cmp	r4, #0
+	bne	loader_loop
+
+jump_to_new_program:
+	adr	r0, launch_message
+	bl	uart_puts
+	mov	r0, #0
+	mov	pc, r0
+
+.align	4
+welcome_banner:
+.ascii	"Fernvale bootloader\r\nWrite four bytes of program size, then\r\n"
+.asciz	"write program data...\r\n>"
+launch_message:
+.asciz	"Launching program...\r\n"
+.align	4
+
+uart_putc:
+	stmfd	sp!, {lr}
+	ldr	r2, =0xa0080014 // uart offset
+uart_putc_ready_wait:
+	ldrb	r1, [r2]
+	tst	r1, #0x20
+	beq	uart_putc_ready_wait
+
+	sub	r2, r2, #0x14
+	strb	r0, [r2]
+	ldmfd	sp!, {pc}
+
+uart_puts:
+	stmfd	sp!, {lr}
+	mov	r3, r0
+
+uart_puts_loop:
+	ldrb	r0, [r3], #1
+	cmp	r0, #0
+	beq	uart_exit
+	bl	uart_putc
+	b	uart_puts_loop
+uart_exit:
+	ldmfd	sp!, {pc}
+
+uart_getc:
+	stmfd	sp!, {lr}
+	ldr	r2, =0xa0080014 // uart offset
+uart_getc_ready_wait:
+	ldrb	r1, [r2]
+	tst	r1, #0x01
+	beq	uart_getc_ready_wait
+
+	sub	r2, r2, #0x14
+	ldrb	r0, [r2]
+	ldmfd	sp!, {pc}
+
+asm_memcpy:
+	mov	r3, r1
+	add	r3, r3, r2
+
+asm_memcpy_loop:
+	cmp	r1, r3
+	ldrcc	r2, [r1], #4
+	strcc	r2, [r0], #4
+	bcc	asm_memcpy_loop
+	bx	lr
+
+wdt_disable:
+	ldr	r1, =0xa0030000
+	mov	r0, #0x2200
+	str	r0, [r1]
+	bx	lr