path: root/mac/main.c

/*
 *   Simple software defined radio lower Medium-Access-Control layer.
 *
 *   Copyright (C) 2008 Michael Buesch <mb@bu3sch.de>
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation; either version 2
 *   of the License, or (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 */

/* Received packets from the PHY look like this:
 *
 * [RF_HEADER] [MAC_HEADER] [PAYLOAD] [CHECKSUM]
 *   3 bytes     3 bytes       var.     CRC-8
 *
 * For a description of the RF_HEADER, see PHY documentation.
 * The payload is opaque and has variable size.
 * The checksum is a CRC-8 over the MAC_HEADER and PAYLOAD.
 *
 * The MAC_HEADER consists of the following fields:
 * [DEST_ADDR] [SRC_ADDR] [SEQ_CTRL]
 *   1 byte      1 byte     1 byte
 *
 * DEST_ADDR is the destination address of the packet.
 * SRC_ADDR is the source address of the packet.
 * SEQ_CTRL is the sequence and fragment control.
 *
 * Transmitted packets look the same, except the RF_HEADER is
 * missing, as it's added in the PHY later.
 */

#include "../mac2phy.h"
#include "../common.h"

#include "util.h"
#include "spi_master.h"
#include "debug.h"

#include <avr/io.h>
#include <avr/interrupt.h>


struct mac_header {
	uint8_t da;
	uint8_t sa;
	uint8_t seq;
} __attribute__((packed));

#define FCS_LEN		1 /* length of the FrameCheckSequence CRC8 */


enum spi_state_id {
	SPI_STATE_IDLE,
	SPI_STATE_GET_RXFRAME_CMD,
	SPI_STATE_GET_RXFRAME,
	SPI_STATE_WAIT_RXFRAME,
	SPI_STATE_PUSH_TXFRAME_CMD,
	SPI_STATE_PUSH_TXFRAME,
	SPI_STATE_WAIT_TXFRAME,
};
struct spi_state {
	/* The SPI statemachine. SPI_STATE_*** */
	uint8_t state;

	union {
		/* Buffer for sending the current command. */
		uint8_t cur_cmd;
		/* Buffer for result codes. */
		uint8_t result_code;
	};
};
static struct spi_state spi_state;

static bool rxpack_available_in_phy;

/* The MAC address of this device. */
static uint8_t mac_address;
/* Promiscuous mode enabled. */
static bool promisc;
/* Bad-packets promiscuous mode enabled. */
static bool promisc_bad;

/* Buffer for a received packet. */
static uint8_t rx_buf[RF_MAX_PACK_SIZE + RF_HEADER_SIZE];
static bool rx_pack_valid;
static uint16_t rx_pack_size;

/* Buffer for a to-be-transmitted packet. */
static uint8_t tx_buf[RF_MAX_PACK_SIZE];
static bool tx_pack_valid;
static uint16_t tx_pack_size;


static inline uint8_t crc8(uint8_t crc, uint8_t data)
{
	/* Polynomial:   x^8 + x^7 + x^6 + x^4 + x^2 + 1   */
	static const prog_uint8_t t[] = {
		0x00, 0xF7, 0xB9, 0x4E, 0x25, 0xD2, 0x9C, 0x6B,
		0x4A, 0xBD, 0xF3, 0x04, 0x6F, 0x98, 0xD6, 0x21,
		0x94, 0x63, 0x2D, 0xDA, 0xB1, 0x46, 0x08, 0xFF,
		0xDE, 0x29, 0x67, 0x90, 0xFB, 0x0C, 0x42, 0xB5,
		0x7F, 0x88, 0xC6, 0x31, 0x5A, 0xAD, 0xE3, 0x14,
		0x35, 0xC2, 0x8C, 0x7B, 0x10, 0xE7, 0xA9, 0x5E,
		0xEB, 0x1C, 0x52, 0xA5, 0xCE, 0x39, 0x77, 0x80,
		0xA1, 0x56, 0x18, 0xEF, 0x84, 0x73, 0x3D, 0xCA,
		0xFE, 0x09, 0x47, 0xB0, 0xDB, 0x2C, 0x62, 0x95,
		0xB4, 0x43, 0x0D, 0xFA, 0x91, 0x66, 0x28, 0xDF,
		0x6A, 0x9D, 0xD3, 0x24, 0x4F, 0xB8, 0xF6, 0x01,
		0x20, 0xD7, 0x99, 0x6E, 0x05, 0xF2, 0xBC, 0x4B,
		0x81, 0x76, 0x38, 0xCF, 0xA4, 0x53, 0x1D, 0xEA,
		0xCB, 0x3C, 0x72, 0x85, 0xEE, 0x19, 0x57, 0xA0,
		0x15, 0xE2, 0xAC, 0x5B, 0x30, 0xC7, 0x89, 0x7E,
		0x5F, 0xA8, 0xE6, 0x11, 0x7A, 0x8D, 0xC3, 0x34,
		0xAB, 0x5C, 0x12, 0xE5, 0x8E, 0x79, 0x37, 0xC0,
		0xE1, 0x16, 0x58, 0xAF, 0xC4, 0x33, 0x7D, 0x8A,
		0x3F, 0xC8, 0x86, 0x71, 0x1A, 0xED, 0xA3, 0x54,
		0x75, 0x82, 0xCC, 0x3B, 0x50, 0xA7, 0xE9, 0x1E,
		0xD4, 0x23, 0x6D, 0x9A, 0xF1, 0x06, 0x48, 0xBF,
		0x9E, 0x69, 0x27, 0xD0, 0xBB, 0x4C, 0x02, 0xF5,
		0x40, 0xB7, 0xF9, 0x0E, 0x65, 0x92, 0xDC, 0x2B,
		0x0A, 0xFD, 0xB3, 0x44, 0x2F, 0xD8, 0x96, 0x61,
		0x55, 0xA2, 0xEC, 0x1B, 0x70, 0x87, 0xC9, 0x3E,
		0x1F, 0xE8, 0xA6, 0x51, 0x3A, 0xCD, 0x83, 0x74,
		0xC1, 0x36, 0x78, 0x8F, 0xE4, 0x13, 0x5D, 0xAA,
		0x8B, 0x7C, 0x32, 0xC5, 0xAE, 0x59, 0x17, 0xE0,
		0x2A, 0xDD, 0x93, 0x64, 0x0F, 0xF8, 0xB6, 0x41,
		0x60, 0x97, 0xD9, 0x2E, 0x45, 0xB2, 0xFC, 0x0B,
		0xBE, 0x49, 0x07, 0xF0, 0x9B, 0x6C, 0x22, 0xD5,
		0xF4, 0x03, 0x4D, 0xBA, 0xD1, 0x26, 0x68, 0x9F,
	};
	return pgm_read_byte(&(t[crc ^ data]));
}

static inline uint8_t crc8_buffer(const void *_buf, uint16_t size)
{
	const uint8_t *buf = _buf;
	uint16_t i;
	uint8_t crc = 0xFF;

	for (i = 0; i < size; i++)
		crc = crc8(crc, buf[i]);
	crc ^= 0xFF;

	return crc;
}

/* RX-packet available notification interrupt from the PHY. */
ISR(INT0_vect)
{
	rxpack_available_in_phy = 1;
}

/* Completion callback from SPI-master code. */
void spi_master_xfer_complete(uint16_t size)
{
	switch (spi_state.state) {
	case SPI_STATE_GET_RXFRAME_CMD:
		spi_master_fetch(&spi_state.result_code,
				 sizeof(spi_state.result_code));
		spi_state.state = SPI_STATE_GET_RXFRAME;
		break;
	case SPI_STATE_GET_RXFRAME:
		if (size != sizeof(spi_state.result_code))
			return;
		if (spi_state.result_code != SPI_ERR_NONE)
			return;
		spi_master_fetch(rx_buf, sizeof(rx_buf));
		spi_state.state = SPI_STATE_WAIT_RXFRAME;
		break;
	case SPI_STATE_WAIT_RXFRAME:
		spi_state.state = SPI_STATE_IDLE;
		if (size && (size < sizeof(rx_buf))) {
			rx_pack_size = size;
			mb();
			rx_pack_valid = 1;
		}
		break;

	case SPI_STATE_PUSH_TXFRAME_CMD:
		spi_master_fetch(&spi_state.result_code,
				 sizeof(spi_state.result_code));
		spi_state.state = SPI_STATE_PUSH_TXFRAME;
		break;
	case SPI_STATE_PUSH_TXFRAME:
		if (size != sizeof(spi_state.result_code))
			return;
		if (spi_state.result_code == SPI_ERR_BUSY) {
			/* Retry */
			spi_state.cur_cmd = SPI_CMD_TXFRAME;
			spi_master_xmit(&spi_state.cur_cmd, sizeof(spi_state.cur_cmd));
			spi_state.state = SPI_STATE_PUSH_TXFRAME_CMD;
			return;
		}
		if (spi_state.result_code != SPI_ERR_NONE)
			return;
		spi_master_xmit(tx_buf, tx_pack_size);
		spi_state.state = SPI_STATE_WAIT_TXFRAME;
		break;
	case SPI_STATE_WAIT_TXFRAME:
		spi_state.state = SPI_STATE_IDLE;
		mb();
		tx_pack_valid = 0;
		break;
	}
}

static void phy_interface_init(void)
{
	/* The PHY notifies us via INT0 if an received packet
	 * is available. The IRQ is triggered by rising edge. */
	MCUCR |= (1 << ISC00) | (1 << ISC01);
	GICR |= (1 << INT0); /* Enable INT0 */
	GIFR |= (1 << INTF0); /* Clear IRQ */

	spi_state.state = SPI_STATE_IDLE;
	spi_master_init();
}

/* There's another received packet available in the PHY.
 * Trigger the transfer of the packet to the MAC. */
static int8_t fetch_rxpack_from_phy(void)
{
	if (spi_state.state != SPI_STATE_IDLE)
		return -1; /* SPI is already doing something. */
	if (rx_pack_valid)
		return -1; /* Buffer is still filled. */

	spi_state.cur_cmd = SPI_CMD_RXFRAME;
	spi_master_xmit(&spi_state.cur_cmd, sizeof(spi_state.cur_cmd));
	spi_state.state = SPI_STATE_GET_RXFRAME_CMD;

	return 0;
}

static int8_t checksum_received_packet(void)
{
	uint8_t expected_crc, calculated_crc;

	if (promisc_bad)
		return 0;
	calculated_crc = crc8_buffer(rx_buf + RF_HEADER_SIZE,
				     rx_pack_size - FCS_LEN - RF_HEADER_SIZE);
	expected_crc = rx_buf[rx_pack_size - 1];
	if (calculated_crc != expected_crc)
		return -1;

	return 0;
}

static int8_t destination_filter(void)
{
	const struct mac_header *hdr = (struct mac_header *)(rx_buf + RF_HEADER_SIZE);

	if (promisc)
		return 0;
	if (hdr->da != mac_address)
		return -1;

	return 0;
}

/* There's a fresh RX-packet in the MAC RX buffer.
 * Handle it and push it to the host. */
static void handle_received_packet(void)
{
	int8_t err;

	if (rx_pack_size < RF_HEADER_SIZE + sizeof(struct mac_header) + FCS_LEN)
		goto drop;
	err = checksum_received_packet();
	if (err)
		goto drop;
	err = destination_filter();
	if (err)
		goto drop;

	//TODO
debug_flip();
goto drop;

	return;

drop:
	mb();
	rx_pack_valid = 0;
	mb();
}

int main(void)
{
	int8_t err;

	cli();

	debug_initialize();
	phy_interface_init();

	sei();

	while (1) {
		/* Run at least 1uS with interrupts enabled. */
		udelay(1);

		cli();
		if (rxpack_available_in_phy) {
			err = fetch_rxpack_from_phy();
			if (!err)
				rxpack_available_in_phy = 0;
		}
		sei();

		mb();
		if (rx_pack_valid)
			handle_received_packet();
	}
}