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Since the i2c bus is bidirectional, there are certain states (eg. part way through a read) where the slave device is in control of driving the SDA line. On a cold start (power on), the slave devices are all quiescent and will not drive the bus. However, on a warm start (eg. watchdog or jtag restart), it is possible that as the CPU boots, the slave device may be holding the SDA line low. This is a bus busy condition and will prevent the I2C bus master in the CPU from being able to seize the bus during init. The fix for this is to clock the i2c bus sufficiently to ensure that the the slave device finishes its transaction and releases the bus. Once the slave has released the bus, the bus master can properly initialize and assert a STOP condition on the bus. git-svn-id: svn://svn.openpilot.org/OpenPilot/trunk@1349 ebee16cc-31ac-478f-84a7-5cbb03baadba
61 lines
1.9 KiB
C
61 lines
1.9 KiB
C
/**
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******************************************************************************
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* @addtogroup PIOS PIOS Core hardware abstraction layer
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* @{
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* @addtogroup PIOS_I2C I2C Functions
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* @{
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*
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* @file pios_i2c.h
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* @author The OpenPilot Team, http://www.openpilot.org Copyright (C) 2010.
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* Parts by Thorsten Klose (tk@midibox.org)
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* @brief I2C functions header.
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* @see The GNU Public License (GPL) Version 3
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*
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*****************************************************************************/
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/*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#ifndef PIOS_I2C_H
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#define PIOS_I2C_H
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#include <stdbool.h>
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/* Global Types */
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enum pios_i2c_txn_direction {
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PIOS_I2C_TXN_READ,
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PIOS_I2C_TXN_WRITE
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};
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struct pios_i2c_txn {
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uint16_t addr;
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enum pios_i2c_txn_direction rw;
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uint32_t len;
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uint8_t * buf;
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};
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/* Public Functions */
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extern int32_t PIOS_I2C_Init(void);
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extern bool PIOS_I2C_Transfer(uint8_t i2c, const struct pios_i2c_txn txn_list[], uint32_t num_txns);
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extern void PIOS_I2C_EV_IRQ_Handler(uint8_t i2c);
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extern void PIOS_I2C_ER_IRQ_Handler(uint8_t i2c);
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#endif /* PIOS_I2C_H */
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/**
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* @}
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* @}
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*/
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