i2c_bit.c

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/*
 * 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.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <stddef.h>
#include <stdint.h>
#include <errno.h>
#include <string.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 ) {
        DBG2 ( "%c", ( 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 ) {
        DBG2 ( "%c", ( state ? '1' : '0' ) );
        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 ) {
        int state;
        state = read_bit ( basher, I2C_BIT_SDA );
        DBG2 ( "%c", ( state ? '+' : '-' ) );
        return state;
}

/**
 * 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;
        int ack;

        /* Send byte */
        DBG2 ( "[send %02x]", byte );
        for ( i = 8 ; i ; i-- ) {
                i2c_send_bit ( basher, byte & 0x80 );
                byte <<= 1;
        }

        /* Check for acknowledgement from slave */
        ack = ( i2c_recv_bit ( basher ) == 0 );
        DBG2 ( "%s", ( ack ? "[acked]" : "[not acked]" ) );

        return ( ack ? 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 byte = 0;
        int i;

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

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

        DBG2 ( "[rcvd %02x]", byte );
        return byte;
}

/**
 * Select I2C device for reading or writing
 *
 * @v basher            Bit-bashing interface
 * @v i2cdev            I2C device
 * @v offset            Starting offset within the 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 offset, unsigned int direction ) {
        unsigned int address;
        int shift;
        unsigned int byte;
        int rc;

        i2c_start ( basher );

        /* Calculate address to appear on bus */
        address = ( ( ( i2cdev->dev_addr |
                        ( offset >> ( 8 * i2cdev->word_addr_len ) ) ) << 1 )
                    | direction );

        /* Send address a byte at a time */
        for ( shift = ( 8 * ( i2cdev->dev_addr_len - 1 ) ) ;
              shift >= 0 ; shift -= 8 ) {
                byte = ( ( address >> shift ) & 0xff );
                if ( ( rc = i2c_send_byte ( basher, byte ) ) != 0 )
                        return rc;
        }

        return 0;
}

/**
 * Reset I2C bus
 *
 * @v basher            Bit-bashing interface
 * @ret rc              Return status code
 *
 * i2c devices often don't have a reset line, so even a reboot or
 * system power cycle is sometimes not enough to bring them back to a
 * known state.
 */
static int i2c_reset ( struct bit_basher *basher ) {
        unsigned int i;
        int sda;

        /* Clock through several cycles, waiting for an opportunity to
         * pull SDA low while SCL is high (which creates a start
         * condition).
         */
        setscl ( basher, 0 );
        setsda ( basher, 1 );
        for ( i = 0 ; i < I2C_RESET_MAX_CYCLES ; i++ ) {
                setscl ( basher, 1 );
                sda = getsda ( basher );
                if ( sda ) {
                        /* Now that the device will see a start, issue it */
                        i2c_start ( basher );
                        /* Stop the bus to leave it in a known good state */
                        i2c_stop ( basher );
                        DBGC ( basher, "I2CBIT %p reset after %d attempts\n",
                               basher, ( i + 1 ) );
                        return 0;
                }
                setscl ( basher, 0 );
        }

        DBGC ( basher, "I2CBIT %p could not reset after %d attempts\n",
               basher, i );
        return -ETIMEDOUT;
}

/**
 * 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;

        DBGC ( basher, "I2CBIT %p reading from device %x: ",
               basher, i2cdev->dev_addr );

        for ( ; ; data++, offset++ ) {

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

                /* Read byte */
                *data = i2c_recv_byte ( basher );
                DBGC ( basher, "%02x ", *data );
        }
        
        DBGC ( basher, "%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;

        DBGC ( basher, "I2CBIT %p writing to device %x: ",
               basher, i2cdev->dev_addr );

        for ( ; ; data++, offset++ ) {

                /* Select device for writing */
                if ( ( rc = i2c_select ( basher, i2cdev, offset,
                                         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 */
                DBGC ( basher, "%02x ", *data );
                if ( ( rc = i2c_send_byte ( basher, *data ) ) != 0 )
                        break;
        }
        
        DBGC ( basher, "%s\n", ( rc ? "failed" : "" ) );
        i2c_stop ( basher );
        return rc;
}

/**
 * Initialise I2C bit-bashing interface
 *
 * @v i2cbit            I2C bit-bashing interface
 * @v bash_op           Bit-basher operations
 */
int init_i2c_bit_basher ( struct i2c_bit_basher *i2cbit,
                          struct bit_basher_operations *bash_op ) {
        struct bit_basher *basher = &i2cbit->basher;
        int rc;

        /* Initialise data structures */
        basher->op = bash_op;
        assert ( basher->op->read != NULL );
        assert ( basher->op->write != NULL );
        i2cbit->i2c.read = i2c_bit_read;
        i2cbit->i2c.write = i2c_bit_write;

        /* Reset I2C bus */
        if ( ( rc = i2c_reset ( basher ) ) != 0 ) {
                DBGC ( basher, "I2CBIT %p could not reset I2C bus: %s\n",
                       basher, strerror ( rc ) );
                return rc;
        }

        return 0;
}