/* bootROM, a very small bootloader for $NAME
 *
 * protocol details:
 * abbrv: H = Host, CPU = C
 *
 * value/cmd              | direction | comment
 * ------------------------------------------------------------
 * 'H'                    | H -> C    | enter bootROM ("HI")
 * 'O'                    | C -> H    | ack bootROM entry ("OH HAI")
 *
 * 'W'0xZZZZZZZZ0xYYYYYYYY| H -> C    | write instr (0xYY...Y) to
 *                                    | address (0xZZ...Z)
 * 'D'                    | C -> H    | instr write done
 *
 * 'R'0xZZZZZZZZ          | H -> C    | read instr from address (0xZZ..Z)
 * 'F'0xYYYYYYYY          | C -> H    | instr read done and return instr
 *
 * 'Q'0xZZZZZZZZ0xYYYYYYYY| H -> C    | write data (0xYY...Y) to
 *                                    | address (0xZZ...Z)
 * 'A'                    | C -> H    | data write done
 *
 * 'T'0xZZZZZZZZ          | H -> C    | read data from address (0xZZ..Z)
 * 'G'0xYYYYYYYY          | C -> H    | read done and return data
 *
 * 'J'0xZZZZZZZZ          | H -> C    | jump to address (0xZZ...Z)
 */

#define UART_BASE 0x1000
#define UART_STATUS (UART_BASE+0x4)
#define UART_RECV (UART_BASE+0x8)
#define UART_TRANS (UART_BASE+0xC)
#define UART_BAUD (UART_BAUD+0x10)

#define UART_TRANS_EMPTY 0
#define UART_RECV_NEW 1

/* TODO:
 * - uart: clear new_receive bit after the byte is copied?
 *   (implementation issue...)
 */

/* {d,i}{read,write}{8,32}:
 * d ... data space
 * i ... instruction space
 */

typedef unsigned char u8;
typedef unsigned int u32;

void send_byte(u8 x)
{
	while(!(dread32(UART_STATUS) & (1 << UART_TRANS_EMPTY)));
	dwrite8(UART_TRANS, x);
}

void send_word(u32 x)
{
	send_byte((x >> 0) & 0xff);
	send_byte((x >> 8) & 0xff);
	send_byte((x >> 16) & 0xff);
	send_byte((x >> 24) & 0xff);
}

u8 recv_byte(void)
{
	u8 ret;
	while(!(dread32(UART_STATUS) & (1 << UART_RECV_NEW)));
	ret = dread8(UART_RECV);
}

u32 recv_word(void)
{
	u32 ret = 0;
	ret |= recv_byte() << 0;
	ret |= recv_byte() << 8;
	ret |= recv_byte() << 16;
	ret |= recv_byte() << 24;
}

void bootrom(void)
{
	u8 cmd;
	u32 addr, instr;
	for(;;) {
		cmd = recv_byte();
		switch(cmd) {
			case 'W':
				addr = recv_word();
				instr = recv_word();
				/* write to programm space */
				iwrite32(addr, instr);
				send_byte('D');
				break;
			case 'R':
				addr = recv_word();
				instr = iread32(addr);
				send_byte('F');
				send_word(instr);
				break;
			case 'Q':
				addr = recv_word();
				instr = recv_word();
				/* write to data space */
				dwrite32(addr, instr);
				send_byte('A');
				break;
			case 'T':
				addr = recv_word();
				instr = dread32(addr);
				send_byte('G');
				send_word(instr);
				break;
			case 'J':
				addr = recv_word();
				jump_to_instr_mem(addr);
				/* this should never return ;) */
				break;
			case 'H':
			default:
				/* OH HAI */
				send_byte('O');
				break;
		}
	}
}

#define TIMEOUT_START 0x13371337
#define DEFAULT_PROG_START 0x200

void main(void)
{
	/* wait for timeout */
	u32 to = TIMEOUT_START;
	u8 rec;

	/* until to is zeros */
	while(to != 0) {
		to--;
		if(dread32(UART_STATUS) & (1 << UART_RECV_NEW)) {
			rec = read8(UART_RECV);
			if(rec == 'H') {
				send_byte('O');
				bootrom();
			}
		}
	}

	/* after timeout jump to instr. mem plz */
	jump_to_instr_mem(DEFAULT_PROG_START);
}