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Bit-banging I2C master.
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platform/sky/dev/i2c.c
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platform/sky/dev/i2c.c
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/*
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* Copyright (c) 2006, Swedish Institute of Computer Science
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)$Id: i2c.c,v 1.1 2006/09/27 09:43:55 bg- Exp $
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*/
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/*
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* Small and portable implementation of a bit-banging I2C bus master.
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*
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* The code should port really easily to platforms other than the
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* msp430 but has some hardcoded constants in it.
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*
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* More info at:
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* http://i2c-bus.org/
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* http://www.esacademy.com/faq/i2c/
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*/
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#include <stdio.h>
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#include <io.h>
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#include <contiki.h>
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#include <dev/spi.h>
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#include <dev/leds.h>
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#include "dev/i2c.h"
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/*
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* On the Tmote sky access to I2C/SPI/UART0 must always be exclusive.
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*/
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#define I2C_ENABLE() (i2c_enable())
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#define I2C_DISABLE() (i2c_disable())
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void i2c_enable(void);
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void i2c_disable(void);
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void i2c_start(void);
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unsigned i2c_read(int send_ack);
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int i2c_write(unsigned);
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void i2c_stop(void);
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#define I2C_PxDIR P3DIR
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#define I2C_PxIN P3IN
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#define I2C_PxOUT P3OUT
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#define I2C_PxSEL P3SEL
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/*
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* SDA == P3.1
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* SCL == P3.3
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*/
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#define SDA 1
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#define SCL 3
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#define SDA_0() (I2C_PxDIR |= BV(SDA)) /* SDA Output */
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#define SDA_1() (I2C_PxDIR &= ~BV(SDA)) /* SDA Input */
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#define SDA_IS_1 (I2C_PxIN & BV(SDA))
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#define SCL_0() (I2C_PxDIR |= BV(SCL)) /* SCL Output */
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#define SCL_1() (I2C_PxDIR &= ~BV(SCL)) /* SCL Input */
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#define SCL_IS_1 (I2C_PxIN & BV(SCL))
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/*
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* Should avoid infinite looping while waiting for SCL_IS_1. xxx/bg
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*/
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#define SCL_WAIT_FOR_1() do{}while (!SCL_IS_1)
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#define delay_4_7us() do{ _NOP(); _NOP(); _NOP(); _NOP(); \
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_NOP(); _NOP(); _NOP(); _NOP(); \
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_NOP(); _NOP(); _NOP(); _NOP(); }while(0)
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#define delay_4us() do{ _NOP(); _NOP(); _NOP(); _NOP(); \
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_NOP(); _NOP(); _NOP(); _NOP(); \
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_NOP(); _NOP(); }while(0)
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static unsigned char old_pxsel, old_pxout, old_pxdir;
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/*
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* Grab SDA and SCL pins for exclusive use but remember old
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* configuration so that it may be restored when we are done.
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*/
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void
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i2c_enable(void)
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{
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unsigned char sda_scl = BV(SDA)|BV(SCL);
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old_pxsel = I2C_PxSEL & sda_scl;
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old_pxout = I2C_PxOUT & sda_scl;
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old_pxdir = I2C_PxDIR & sda_scl;
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spi_busy = 1;
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I2C_PxSEL &= ~sda_scl;
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I2C_PxOUT &= ~sda_scl;
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I2C_PxDIR |= BV(SCL); /* SCL Output */
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I2C_PxDIR &= ~BV(SDA); /* SDA Input */
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}
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/*
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* Restore bus to what it was before i2c_enable.
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*
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*/
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void
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i2c_disable(void)
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{
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unsigned char not_sda_scl = ~(BV(SDA)|BV(SCL));
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I2C_PxDIR = (I2C_PxDIR & not_sda_scl) | old_pxdir;
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I2C_PxOUT = (I2C_PxOUT & not_sda_scl) | old_pxout;
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I2C_PxSEL = (I2C_PxSEL & not_sda_scl) | old_pxsel;
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spi_busy = 0;
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}
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void
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i2c_start(void)
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{
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SDA_1();
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SCL_1();
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SCL_WAIT_FOR_1();
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delay_4_7us();
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SDA_0();
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delay_4us();
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SCL_0();
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}
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void
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i2c_stop(void)
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{
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SDA_0();
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delay_4us();
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SCL_1();
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SCL_WAIT_FOR_1();
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SDA_1();
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}
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/*
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* Return true if we received an ACK.
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*/
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int
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i2c_write(unsigned _c)
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{
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unsigned char c = _c;
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unsigned long n;
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int i;
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int ret;
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for (i = 0; i < 8; i++, c <<= 1) {
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if (c & 0x80)
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SDA_1();
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else
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SDA_0();
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SCL_1();
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SCL_WAIT_FOR_1();
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SCL_0();
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}
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SDA_1();
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SCL_1();
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ret = 0; /* Loop waiting for an ACK to arrive. */
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for (n = 0; n < 250000; n++) {
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if (!SDA_IS_1) {
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ret = 1;
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break;
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}
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}
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SCL_WAIT_FOR_1(); /* clock stretching? */
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SCL_0();
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return ret;
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}
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unsigned
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i2c_read(int send_ack)
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{
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int i;
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unsigned char c = 0x00;
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SDA_1();
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for (i = 0; i < 8; i++) {
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c <<= 1;
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SCL_1();
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SCL_WAIT_FOR_1();
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if (SDA_IS_1)
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c |= 0x1;
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SCL_0();
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}
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if (send_ack)
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SDA_0();
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SCL_1();
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SCL_WAIT_FOR_1();
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SCL_0();
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return c;
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}
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43
platform/sky/dev/i2c.h
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43
platform/sky/dev/i2c.h
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@ -0,0 +1,43 @@
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/*
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* Copyright (c) 2006, Swedish Institute of Computer Science
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)$Id: i2c.h,v 1.1 2006/09/27 09:43:55 bg- Exp $
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*/
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#ifndef I2C_H
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#define I2C_H
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void i2c_enable(void);
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void i2c_disable(void);
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void i2c_start(void);
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void i2c_stop(void);
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int i2c_write(unsigned);
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unsigned i2c_read(int send_ack);
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#endif /* I2C_H */
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