#define F_CPU 8000000
#include <stdint.h>
#include <stdbool.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <util/delay.h>

const uint8_t __signature[3] __attribute__((section (".signature"), used)) =
        { SIGNATURE_2, SIGNATURE_1, SIGNATURE_0 };

#include "uart.c"

#define B_SCK	5
#define B_MISO	4
#define B_MOSI	3
#define B_SS	2

#define spi_ss(x)	PORTB = ((x) << B_SS) | 0x3;

static volatile bool canint = false;

ISR(INT0_vect)
{
	uart_puts("can: interrupt\n");
	canint = true;	
}

static uint8_t spi_wrrd(uint8_t out)
{
	SPDR = out;
	while (!(SPSR & (1 << SPIF)))
		;
	return SPDR;
}

static void spi_performpgm(const uint8_t * PROGMEM cmds, uint8_t len)
{
	const uint8_t * PROGMEM end = cmds + len;
	uint8_t c;

	spi_ss(0);
	while (cmds < end) {
		c = pgm_read_byte(cmds);
		spi_wrrd(c);
		cmds++;
	}
	spi_ss(1);
}
#define spi_perform(...) do { \
	static const uint8_t _mycmds[] PROGMEM = { __VA_ARGS__ }; \
	spi_performpgm(_mycmds, sizeof(_mycmds)); } while (0)

/* CAN configuration:
 *
 * CNF1	SJW	= 1TQ	00xxxxxx
 * 	BRP	= /12	xx001011	(16 MHz assumed)
 * 	= 0x0b
 * CNF2 BTLMODE = cfg	1xxxxxxx
 * 	SAM	= once	x0xxxxxx
 * 	PS1	= 1TQ	xx000xxx
 * 	prop	= 2TQ	xxxxx001
 * 	= 0x81
 * CNF3	WAKFIL	= off	x0xxxxxx
 * 	PS2	= 2TQ	xxxxx001
 * 	= 0x01
 */

#define MCP2515_WRITE	0x02
#define MCP2515_READ	0x03
#define MCP2515_RTS	0x80

#define A_CNF3		0x28
#define A_CANINTF	0x2c
#define A_CANCTRL	0x2f
#define A_TXB0CTRL	0x30
#define A_TXB0SIDH	0x31
#define A_RXB1CTRL	0x70

static void can_init(void)
{
	spi_perform(MCP2515_WRITE, A_CANCTRL,
		0x80);	/* CANCTRL: config mode */
	spi_perform(MCP2515_WRITE, A_CNF3,
		0x01,	/* CNF3 */
		0x81,	/* CNF2 */
		0x0b,	/* CNF1 */
		0xa4	/* CANINTE: MERRE, ERRIE, TX0IE */
	);
	spi_perform(MCP2515_WRITE, A_RXB1CTRL,
		0x60);	/* x, RXM, x, RXRTR, FILHIT */
	spi_perform(MCP2515_WRITE, A_CANCTRL,
		0x00);	/* CANCTRL: normal mode */
}

static uint8_t can_CANSTAT(void)
{
	uint8_t canstat;

	spi_ss(0);
	spi_wrrd(0x03);
	spi_wrrd(0x2e);	/* addr(CANCTRL) */
	canstat = spi_wrrd(0xff);	/* CANSTAT */
	spi_ss(1);
	uart_puts("can: CANSTAT ");
	uart_puthex(canstat);
	uart_puts("\n");
	return canstat;
}

static void can_send(void)
{
	uart_puts("can: transmit\n");
	spi_perform(MCP2515_WRITE, A_TXB0SIDH,
		0x55,	/* ID 10:3 */
		0x40,	/* ID 2:0, x, EXIDE, x, EID 17:16 */
		0x00,	/* EID 15:8 */
		0x00,	/* EID 7:0 */
		0x00);	/* x, RTR, xx, DLC */
	spi_perform(MCP2515_RTS | 0x01);
}

static void can_int(void)
{
	uint8_t canintf, eflg, canstat;

	uart_puts("can: irqh<");

	spi_ss(0);
	spi_wrrd(MCP2515_READ);
	spi_wrrd(A_CANINTF);
	canintf	= spi_wrrd(0xff);
	eflg	= spi_wrrd(0xff);
	canstat = spi_wrrd(0xff);
	spi_ss(1);

	uart_puthex(canintf);
	uart_puthex(eflg);
	uart_puthex(canstat);
	uart_puts(">\n");

	if (canintf & 0x80 || canintf & 0x04) {
		uint8_t txb0ctrl;
		spi_ss(0);
		spi_wrrd(0x03);
		spi_wrrd(0x30);
		txb0ctrl = spi_wrrd(0xff);
		spi_ss(1);
		uart_puts("can: TXB0CTRL ");
		uart_puthex(txb0ctrl);
		uart_puts("\n");
	}
	if (canintf & 0x02) {
		uint8_t rxb1dlc, c;
		uart_puts("can: RX1IF\n");
		spi_ss(0);
		spi_wrrd(0x94);
		uart_puthex(spi_wrrd(0xff));
		uart_puthex(spi_wrrd(0xff));
		uart_puthex(spi_wrrd(0xff));
		uart_puthex(spi_wrrd(0xff));
		rxb1dlc = spi_wrrd(0xff);
		uart_puthex(rxb1dlc);
		uart_puts("\n");
		for (c = 0; c < rxb1dlc; c++)
			uart_puthex(spi_wrrd(0xff));
		uart_puts("\n");
		spi_ss(1);
	}

	spi_perform(MCP2515_WRITE, A_CANINTF, 0x00);
}

int main(void)
{
	uint8_t status;

	uart_init();

	spi_ss(1);
	DDRB = (1 << B_SCK) | (1 << B_MOSI) | (1 << B_SS);

	/* divisor: 0 0 0 = fosc / 4 = 2 MHz */
	SPCR = (1 << SPE) | (1 << MSTR);

	/* INT0 */
	EICRA = (1 << ISC01);
	EIMSK = (1 << INT0);

	sei();

	uart_puts("\nspi: init ok\n");
	_delay_ms(50);

	spi_ss(0);
	spi_wrrd(0xc0);
	spi_ss(1);

	_delay_ms(50);
	spi_ss(0);
	spi_wrrd(0xb0);
	status = spi_wrrd(0xff);
	spi_ss(1);
	uart_puts("can: status ");
	uart_puthex(status);
	uart_puts("\n");

	can_init();
	can_CANSTAT();

	while (1) {
		if (canint) {
			canint = false;
			can_int();
		}
		_delay_ms(25);
	}
}

void __do_copy_data(void) __attribute__((naked, section (".init4"), used));
void __do_copy_data(void) { }