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Bit-banging I2C master.

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bg- 2006-09-27 09:43:55 +00:00
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commit fa02e72526
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platform/sky/dev/i2c.c Normal file
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/*
* Copyright (c) 2006, Swedish Institute of Computer Science
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)$Id: i2c.c,v 1.1 2006/09/27 09:43:55 bg- Exp $
*/
/*
* Small and portable implementation of a bit-banging I2C bus master.
*
* The code should port really easily to platforms other than the
* msp430 but has some hardcoded constants in it.
*
* More info at:
* http://i2c-bus.org/
* http://www.esacademy.com/faq/i2c/
*/
#include <stdio.h>
#include <io.h>
#include <contiki.h>
#include <dev/spi.h>
#include <dev/leds.h>
#include "dev/i2c.h"
/*
* On the Tmote sky access to I2C/SPI/UART0 must always be exclusive.
*/
#define I2C_ENABLE() (i2c_enable())
#define I2C_DISABLE() (i2c_disable())
void i2c_enable(void);
void i2c_disable(void);
void i2c_start(void);
unsigned i2c_read(int send_ack);
int i2c_write(unsigned);
void i2c_stop(void);
#define I2C_PxDIR P3DIR
#define I2C_PxIN P3IN
#define I2C_PxOUT P3OUT
#define I2C_PxSEL P3SEL
/*
* SDA == P3.1
* SCL == P3.3
*/
#define SDA 1
#define SCL 3
#define SDA_0() (I2C_PxDIR |= BV(SDA)) /* SDA Output */
#define SDA_1() (I2C_PxDIR &= ~BV(SDA)) /* SDA Input */
#define SDA_IS_1 (I2C_PxIN & BV(SDA))
#define SCL_0() (I2C_PxDIR |= BV(SCL)) /* SCL Output */
#define SCL_1() (I2C_PxDIR &= ~BV(SCL)) /* SCL Input */
#define SCL_IS_1 (I2C_PxIN & BV(SCL))
/*
* Should avoid infinite looping while waiting for SCL_IS_1. xxx/bg
*/
#define SCL_WAIT_FOR_1() do{}while (!SCL_IS_1)
#define delay_4_7us() do{ _NOP(); _NOP(); _NOP(); _NOP(); \
_NOP(); _NOP(); _NOP(); _NOP(); \
_NOP(); _NOP(); _NOP(); _NOP(); }while(0)
#define delay_4us() do{ _NOP(); _NOP(); _NOP(); _NOP(); \
_NOP(); _NOP(); _NOP(); _NOP(); \
_NOP(); _NOP(); }while(0)
static unsigned char old_pxsel, old_pxout, old_pxdir;
/*
* Grab SDA and SCL pins for exclusive use but remember old
* configuration so that it may be restored when we are done.
*/
void
i2c_enable(void)
{
unsigned char sda_scl = BV(SDA)|BV(SCL);
old_pxsel = I2C_PxSEL & sda_scl;
old_pxout = I2C_PxOUT & sda_scl;
old_pxdir = I2C_PxDIR & sda_scl;
spi_busy = 1;
I2C_PxSEL &= ~sda_scl;
I2C_PxOUT &= ~sda_scl;
I2C_PxDIR |= BV(SCL); /* SCL Output */
I2C_PxDIR &= ~BV(SDA); /* SDA Input */
}
/*
* Restore bus to what it was before i2c_enable.
*
*/
void
i2c_disable(void)
{
unsigned char not_sda_scl = ~(BV(SDA)|BV(SCL));
I2C_PxDIR = (I2C_PxDIR & not_sda_scl) | old_pxdir;
I2C_PxOUT = (I2C_PxOUT & not_sda_scl) | old_pxout;
I2C_PxSEL = (I2C_PxSEL & not_sda_scl) | old_pxsel;
spi_busy = 0;
}
void
i2c_start(void)
{
SDA_1();
SCL_1();
SCL_WAIT_FOR_1();
delay_4_7us();
SDA_0();
delay_4us();
SCL_0();
}
void
i2c_stop(void)
{
SDA_0();
delay_4us();
SCL_1();
SCL_WAIT_FOR_1();
SDA_1();
}
/*
* Return true if we received an ACK.
*/
int
i2c_write(unsigned _c)
{
unsigned char c = _c;
unsigned long n;
int i;
int ret;
for (i = 0; i < 8; i++, c <<= 1) {
if (c & 0x80)
SDA_1();
else
SDA_0();
SCL_1();
SCL_WAIT_FOR_1();
SCL_0();
}
SDA_1();
SCL_1();
ret = 0; /* Loop waiting for an ACK to arrive. */
for (n = 0; n < 250000; n++) {
if (!SDA_IS_1) {
ret = 1;
break;
}
}
SCL_WAIT_FOR_1(); /* clock stretching? */
SCL_0();
return ret;
}
unsigned
i2c_read(int send_ack)
{
int i;
unsigned char c = 0x00;
SDA_1();
for (i = 0; i < 8; i++) {
c <<= 1;
SCL_1();
SCL_WAIT_FOR_1();
if (SDA_IS_1)
c |= 0x1;
SCL_0();
}
if (send_ack)
SDA_0();
SCL_1();
SCL_WAIT_FOR_1();
SCL_0();
return c;
}

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platform/sky/dev/i2c.h Normal file
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/*
* Copyright (c) 2006, Swedish Institute of Computer Science
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)$Id: i2c.h,v 1.1 2006/09/27 09:43:55 bg- Exp $
*/
#ifndef I2C_H
#define I2C_H
void i2c_enable(void);
void i2c_disable(void);
void i2c_start(void);
void i2c_stop(void);
int i2c_write(unsigned);
unsigned i2c_read(int send_ack);
#endif /* I2C_H */