ipxe/src/drivers/bitbash/i2c_bit.c

/*
 * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * 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 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <stddef.h>
#include <stdint.h>
#include <errno.h>
#include <assert.h>
#include <unistd.h>
#include <gpxe/bitbash.h>
#include <gpxe/i2c.h>

/** @file
 *
 * I2C bit-bashing interface
 *
 * This implements a simple I2C master via a bit-bashing interface
 * that provides two lines: SCL (clock) and SDA (data).
 */

/**
 * Delay between output state changes
 *
 * Max rated i2c speed (for the basic i2c protocol) is 100kbps,
 * i.e. 200k clock transitions per second.
 */
static void i2c_delay ( void ) {
	udelay ( I2C_UDELAY );
}

/**
 * Set state of I2C SCL line
 *
 * @v basher		Bit-bashing interface
 * @v state		New state of SCL
 */
static void setscl ( struct bit_basher *basher, int state ) {
	write_bit ( basher, I2C_BIT_SCL, state );
	i2c_delay();
}

/**
 * Set state of I2C SDA line
 *
 * @v basher		Bit-bashing interface
 * @v state		New state of SDA
 */
static void setsda ( struct bit_basher *basher, int state ) {
	write_bit ( basher, I2C_BIT_SDA, state );
	i2c_delay();
}

/**
 * Get state of I2C SDA line
 *
 * @v basher		Bit-bashing interface
 * @ret state		State of SDA
 */
static int getsda ( struct bit_basher *basher ) {
	return read_bit ( basher, I2C_BIT_SDA );
}

/**
 * Send an I2C start condition
 *
 * @v basher		Bit-bashing interface
 */
static void i2c_start ( struct bit_basher *basher ) {
	setscl ( basher, 1 );
	setsda ( basher, 0 );
	setscl ( basher, 0 );
	setsda ( basher, 1 );
}

/**
 * Send an I2C data bit
 *
 * @v basher		Bit-bashing interface
 * @v bit		Bit to send
 */
static void i2c_send_bit ( struct bit_basher *basher, int bit ) {
	setsda ( basher, bit );
	setscl ( basher, 1 );
	setscl ( basher, 0 );
	setsda ( basher, 1 );
}

/**
 * Receive an I2C data bit
 *
 * @v basher		Bit-bashing interface
 * @ret bit		Received bit
 */
static int i2c_recv_bit ( struct bit_basher *basher ) {
	int bit;

	setscl ( basher, 1 );
	bit = getsda ( basher );
	setscl ( basher, 0 );
	return bit;
}

/**
 * Send an I2C stop condition
 *
 * @v basher		Bit-bashing interface
 */
static void i2c_stop ( struct bit_basher *basher ) {
	setsda ( basher, 0 );
	setscl ( basher, 1 );
	setsda ( basher, 1 );
}

/**
 * Send byte via I2C bus and check for acknowledgement
 *
 * @v basher		Bit-bashing interface
 * @v byte		Byte to send
 * @ret rc		Return status code
 *
 * Sends a byte via the I2C bus and checks for an acknowledgement from
 * the slave device.
 */
static int i2c_send_byte ( struct bit_basher *basher, uint8_t byte ) {
	int i;
	
	/* Send byte */
	for ( i = 8 ; i ; i-- ) {
		i2c_send_bit ( basher, byte & 0x80 );
		byte <<= 1;
	}

	/* Check for acknowledgement from slave */
	return ( i2c_recv_bit ( basher ) == 0 ? 0 : -EIO );
}

/**
 * Receive byte via I2C bus
 *
 * @v basher		Bit-bashing interface
 * @ret byte		Received byte
 *
 * Receives a byte via the I2C bus and sends NACK to the slave device.
 */
static uint8_t i2c_recv_byte ( struct bit_basher *basher ) {
	uint8_t value = 0;
	int i;

	/* Receive byte */
	for ( i = 8 ; i ; i-- ) {
		value <<= 1;
		value |= ( i2c_recv_bit ( basher ) & 0x1 );
	}

	/* Send NACK */
	i2c_send_bit ( basher, 1 );

	return value;
}

/**
 * Select I2C device for reading or writing
 *
 * @v basher		Bit-bashing interface
 * @v i2cdev		I2C device
 * @v direction		I2C_READ or I2C_WRITE
 * @ret rc		Return status code
 */
static int i2c_select ( struct bit_basher *basher, struct i2c_device *i2cdev,
			unsigned int direction ) {
	unsigned int address;
	int rc;

	i2c_start ( basher );

	/* First byte of the address */
	address = i2cdev->address;
	if ( i2cdev->tenbit ) {
		address |= I2C_TENBIT_ADDRESS;
		address >>= 8;
	}
	if ( ( rc = i2c_send_byte ( basher, 
				    ( ( address << 1 ) | direction ) ) ) != 0 )
		return rc;

	/* Second byte of the address (10-bit addresses only) */
	if ( i2cdev->tenbit ) {
		if ( ( rc = i2c_send_byte ( basher,
					    ( i2cdev->address & 0xff ) ) ) !=0)
			return rc;
	}

	return 0;
}

/**
 * Read data from I2C device via bit-bashing interface
 *
 * @v i2c		I2C interface
 * @v i2cdev		I2C device
 * @v offset		Starting offset within the device
 * @v data		Data buffer
 * @v len		Length of data buffer
 * @ret rc		Return status code
 *
 * Note that attempting to read zero bytes of data is a valid way to
 * check for I2C device presence.
 */
static int i2c_bit_read ( struct i2c_interface *i2c,
			  struct i2c_device *i2cdev, unsigned int offset,
			  uint8_t *data, unsigned int len ) {
	struct i2c_bit_basher *i2cbit
		= container_of ( i2c, struct i2c_bit_basher, i2c );
	struct bit_basher *basher = &i2cbit->basher;
	int rc = 0;

	DBG ( "Reading from I2C device %x: ", i2cdev->address );

	while ( 1 ) {

		/* Select device for writing */
		if ( ( rc = i2c_select ( basher, i2cdev, I2C_WRITE ) ) != 0 )
			break;

		/* Abort at end of data */
		if ( ! ( len-- ) )
			break;

		/* Select offset */
		if ( ( rc = i2c_send_byte ( basher, offset++ ) ) != 0 )
			break;
		
		/* Select device for reading */
		if ( ( rc = i2c_select ( basher, i2cdev, I2C_READ ) ) != 0 )
			break;

		/* Read byte */
		*data++ = i2c_recv_byte ( basher );
		DBG ( "%02x ", *(data - 1) );
	}
	
	DBG ( "%s\n", ( rc ? "failed" : "" ) );
	i2c_stop ( basher );
	return rc;
}

/**
 * Write data to I2C device via bit-bashing interface
 *
 * @v i2c		I2C interface
 * @v i2cdev		I2C device
 * @v offset		Starting offset within the device
 * @v data		Data buffer
 * @v len		Length of data buffer
 * @ret rc		Return status code
 *
 * Note that attempting to write zero bytes of data is a valid way to
 * check for I2C device presence.
 */
static int i2c_bit_write ( struct i2c_interface *i2c,
			   struct i2c_device *i2cdev, unsigned int offset,
			   const uint8_t *data, unsigned int len ) {
	struct i2c_bit_basher *i2cbit
		= container_of ( i2c, struct i2c_bit_basher, i2c );
	struct bit_basher *basher = &i2cbit->basher;
	int rc = 0;

	DBG ( "Writing to I2C device %x: ", i2cdev->address );

	while ( 1 ) {

		/* Select device for writing */
		if ( ( rc = i2c_select ( basher, i2cdev, I2C_WRITE ) ) != 0 )
			break;
		
		/* Abort at end of data */
		if ( ! ( len-- ) )
			break;

		/* Select offset */
		if ( ( rc = i2c_send_byte ( basher, offset++ ) ) != 0 )
			break;
		
		/* Write data to device */
		DBG ( "%02x ", *data );
		if ( ( rc = i2c_send_byte ( basher, *data++ ) ) != 0 )
			break;
	}
	
	DBG ( "%s\n", ( rc ? "failed" : "" ) );
	i2c_stop ( basher );
	return rc;
}

/**
 * Initialise I2C bit-bashing interface
 *
 * @v i2cbit		I2C bit-bashing interface
 */
void init_i2c_bit_basher ( struct i2c_bit_basher *i2cbit ) {
	struct bit_basher *basher = &i2cbit->basher;
	
	assert ( basher->op->read != NULL );
	assert ( basher->op->write != NULL );
	i2cbit->i2c.read = i2c_bit_read;
	i2cbit->i2c.write = i2c_bit_write;
	i2c_stop ( basher );
}