PX4-Autopilot/src/lib/drivers/smbus/SMBus.cpp

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/**
 * @file SMBus.cpp
 * SMBus v2.0 protocol implementation.
 *
 * @author Jacob Dahl <dahl.jakejacob@gmail.com>
 *
 * TODO
 *  - Enable SMBus mode at the NuttX level. This may be tricky sharing the bus with i2c.
 *  	i.e STM32f4 see platforms/nuttx/Nuttx/nuttx/arch/arm/src/stm32/stm32f40xxx_i2c.c
 *  - Add remaining SMBus protocol messages as needed
 */

#include "SMBus.hpp"

SMBus::SMBus(int bus_num, uint16_t address) :
	I2C("BATT_SMBUS_I2C", nullptr, bus_num, address, 100000)
{
}

int SMBus::read_word(const uint8_t cmd_code, void *data)
{
	// 2 data bytes + pec byte
	int result = transfer(&cmd_code, 1, (uint8_t *)data, 3);

	if (result == PX4_OK) {
		// Check PEC.
		uint8_t addr = get_device_address() << 1;
		uint8_t full_data_packet[5];
		full_data_packet[0] = addr | 0x00;
		full_data_packet[1] = cmd_code;
		full_data_packet[2] = addr | 0x01;
		memcpy(&full_data_packet[3], data, 2);

		uint8_t pec = get_pec(full_data_packet, sizeof(full_data_packet) / sizeof(full_data_packet[0]));

		if (pec != ((uint8_t *)data)[2]) {
			result = -EINVAL;
		}
	}

	return result;
}

int SMBus::write_word(const uint8_t cmd_code, void *data)
{
	// 2 data bytes + pec byte
	uint8_t buf[5] = {};
	buf[0] = (get_device_address() << 1) | 0x10;
	buf[1] = cmd_code;
	buf[2] = ((uint8_t *)data)[0];
	buf[3] = ((uint8_t *)data)[1];

	buf[4] = get_pec(buf, 4);

	int result = transfer(&buf[1], 4, nullptr, 0);

	return result;
}

int SMBus::block_read(const uint8_t cmd_code, void *data, const uint8_t length, bool use_pec)
{
	unsigned byte_count = 0;
	// addr(wr), cmd_code, addr(r), byte_count, data (32 bytes max), pec
	uint8_t rx_data[32 + 5];

	int result = transfer(&cmd_code, 1, (uint8_t *)&rx_data[3], length + 2);

	uint8_t device_address = get_device_address();
	rx_data[0] = (device_address << 1) | 0x00;
	rx_data[1] = cmd_code;
	rx_data[2] = (device_address << 1) | 0x01;
	byte_count = rx_data[3];

	memcpy(data, &rx_data[4], byte_count);

	if (use_pec) {
		uint8_t pec = get_pec(rx_data, byte_count + 4);

		if (pec != rx_data[byte_count + 4]) {
			result = -EINVAL;
		}
	}

	return result;
}

int SMBus::block_write(const uint8_t cmd_code, void *data, uint8_t byte_count, bool use_pec)
{
	// cmd code[1], byte count[1], data[byte_count] (32max), pec[1] (optional)
	uint8_t buf[32 + 2];

	buf[0] = cmd_code;
	buf[1] = (uint8_t)byte_count;
	memcpy(&buf[2], data, byte_count);

	if (use_pec) {
		uint8_t pec = get_pec(buf, byte_count + 2);
		buf[byte_count + 2] = pec;
		byte_count++;
	}

	unsigned i = 0;
	int result = 0;

	// If block_write fails, try up to 10 times.
	while (i < 10 && ((result = transfer((uint8_t *)buf, byte_count + 2, nullptr, 0)) != PX4_OK)) {
		i++;
	}

	if (i == 10 || result) {
		PX4_WARN("Block_write failed %d times", i);
		result = -EINVAL;
	}

	return result;
}

uint8_t SMBus::get_pec(uint8_t *buff, const uint8_t len)
{
	// Initialise CRC to zero.
	uint8_t crc = 0;
	uint8_t shift_register = 0;
	bool invert_crc;

	// Calculate crc for each byte in the stream.
	for (uint8_t i = 0; i < len; i++) {
		// Load next data byte into the shift register
		shift_register = buff[i];

		// Calculate crc for each bit in the current byte.
		for (uint8_t j = 0; j < 8; j++) {
			invert_crc = (crc ^ shift_register) & 0x80;
			crc <<= 1;
			shift_register <<= 1;

			if (invert_crc) {
				crc ^= SMBUS_PEC_POLYNOMIAL;
			}
		}
	}

	return crc;
}