265 lines
6.3 KiB
C
265 lines
6.3 KiB
C
/*
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* Copyright (c) 2017 Linaro Ltd.
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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/**
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* @file
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* @brief Software driven 'bit-banging' library for I2C
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*
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* This code implements the I2C single master protocol in software by directly
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* manipulating the levels of the SCL and SDA lines of an I2C bus. It supports
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* the Standard-mode and Fast-mode speeds and doesn't support optional
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* protocol feature like 10-bit addresses or clock stretching.
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*
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* Timings and protocol are based Rev. 6 of the I2C specification:
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* http://www.nxp.com/documents/user_manual/UM10204.pdf
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*/
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#include <errno.h>
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#include <kernel.h>
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#include <drivers/i2c.h>
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#include "i2c_bitbang.h"
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/*
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* Indexes into delay table for each part of I2C timing waveform we are
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* interested in. In practice, for Standard and Fast modes, there are only two
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* different numerical values (T_LOW and T_HIGH) so we alias the others to
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* these. (Actually, we're simplifying a little, T_SU_STA could be T_HIGH on
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* Fast mode)
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*/
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#define T_LOW 0
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#define T_HIGH 1
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#define T_SU_STA T_LOW
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#define T_HD_STA T_HIGH
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#define T_SU_STP T_HIGH
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#define T_BUF T_LOW
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#define NS_TO_SYS_CLOCK_HW_CYCLES(ns) \
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((u64_t)sys_clock_hw_cycles_per_sec() * (ns) / NSEC_PER_SEC + 1)
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int i2c_bitbang_configure(struct i2c_bitbang *context, u32_t dev_config)
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{
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/* Check for features we don't support */
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if (I2C_ADDR_10_BITS & dev_config) {
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return -ENOTSUP;
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}
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/* Setup speed to use */
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switch (I2C_SPEED_GET(dev_config)) {
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case I2C_SPEED_STANDARD:
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context->delays[T_LOW] = NS_TO_SYS_CLOCK_HW_CYCLES(4700);
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context->delays[T_HIGH] = NS_TO_SYS_CLOCK_HW_CYCLES(4000);
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break;
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case I2C_SPEED_FAST:
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context->delays[T_LOW] = NS_TO_SYS_CLOCK_HW_CYCLES(1300);
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context->delays[T_HIGH] = NS_TO_SYS_CLOCK_HW_CYCLES(600);
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break;
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default:
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return -ENOTSUP;
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}
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return 0;
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}
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static void i2c_set_scl(struct i2c_bitbang *context, int state)
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{
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context->io->set_scl(context->io_context, state);
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}
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static void i2c_set_sda(struct i2c_bitbang *context, int state)
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{
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context->io->set_sda(context->io_context, state);
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}
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static int i2c_get_sda(struct i2c_bitbang *context)
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{
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return context->io->get_sda(context->io_context);
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}
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static void i2c_delay(unsigned int cycles_to_wait)
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{
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u32_t start = k_cycle_get_32();
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/* Wait until the given number of cycles have passed */
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while (k_cycle_get_32() - start < cycles_to_wait) {
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}
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}
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static void i2c_start(struct i2c_bitbang *context)
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{
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if (!i2c_get_sda(context)) {
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/*
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* SDA is already low, so we need to do something to make it
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* high. Try pulsing clock low to get slave to release SDA.
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*/
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i2c_set_scl(context, 0);
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i2c_delay(context->delays[T_LOW]);
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i2c_set_scl(context, 1);
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i2c_delay(context->delays[T_SU_STA]);
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}
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i2c_set_sda(context, 0);
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i2c_delay(context->delays[T_HD_STA]);
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}
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static void i2c_repeated_start(struct i2c_bitbang *context)
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{
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i2c_delay(context->delays[T_SU_STA]);
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i2c_start(context);
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}
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static void i2c_stop(struct i2c_bitbang *context)
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{
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if (i2c_get_sda(context)) {
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/*
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* SDA is already high, so we need to make it low so that
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* we can create a rising edge. This means we're effectively
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* doing a START.
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*/
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i2c_delay(context->delays[T_SU_STA]);
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i2c_set_sda(context, 0);
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i2c_delay(context->delays[T_HD_STA]);
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}
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i2c_delay(context->delays[T_SU_STP]);
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i2c_set_sda(context, 1);
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i2c_delay(context->delays[T_BUF]); /* In case we start again too soon */
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}
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static void i2c_write_bit(struct i2c_bitbang *context, int bit)
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{
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i2c_set_scl(context, 0);
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/* SDA hold time is zero, so no need for a delay here */
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i2c_set_sda(context, bit);
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i2c_delay(context->delays[T_LOW]);
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i2c_set_scl(context, 1);
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i2c_delay(context->delays[T_HIGH]);
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}
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static bool i2c_read_bit(struct i2c_bitbang *context)
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{
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bool bit;
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i2c_set_scl(context, 0);
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/* SDA hold time is zero, so no need for a delay here */
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i2c_set_sda(context, 1); /* Stop driving low, so slave has control */
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i2c_delay(context->delays[T_LOW]);
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bit = i2c_get_sda(context);
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i2c_set_scl(context, 1);
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i2c_delay(context->delays[T_HIGH]);
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return bit;
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}
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static bool i2c_write_byte(struct i2c_bitbang *context, u8_t byte)
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{
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u8_t mask = 1 << 7;
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do {
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i2c_write_bit(context, byte & mask);
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} while (mask >>= 1);
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/* Return inverted ACK bit, i.e. 'true' for ACK, 'false' for NACK */
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return !i2c_read_bit(context);
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}
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static u8_t i2c_read_byte(struct i2c_bitbang *context)
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{
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unsigned int byte = 1U;
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do {
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byte <<= 1;
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byte |= i2c_read_bit(context);
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} while (!(byte & (1 << 8)));
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return byte;
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}
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int i2c_bitbang_transfer(struct i2c_bitbang *context,
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struct i2c_msg *msgs, u8_t num_msgs,
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u16_t slave_address)
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{
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u8_t *buf, *buf_end;
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unsigned int flags;
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int result = -EIO;
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if (!num_msgs) {
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return 0;
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}
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/* We want an initial Start condition */
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flags = I2C_MSG_RESTART;
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/* Make sure we're in a good state so slave recognises the Start */
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i2c_set_scl(context, 1);
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flags |= I2C_MSG_STOP;
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do {
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/* Stop flag from previous message? */
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if (flags & I2C_MSG_STOP) {
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i2c_stop(context);
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}
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/* Forget old flags except start flag */
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flags &= I2C_MSG_RESTART;
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/* Start condition? */
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if (flags & I2C_MSG_RESTART) {
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i2c_start(context);
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} else if (msgs->flags & I2C_MSG_RESTART) {
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i2c_repeated_start(context);
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}
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/* Get flags for new message */
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flags |= msgs->flags;
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/* Send address after any Start condition */
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if (flags & I2C_MSG_RESTART) {
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unsigned int byte0 = slave_address << 1;
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byte0 |= (flags & I2C_MSG_RW_MASK) == I2C_MSG_READ;
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if (!i2c_write_byte(context, byte0)) {
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goto finish; /* No ACK received */
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}
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flags &= ~I2C_MSG_RESTART;
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}
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/* Transfer data */
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buf = msgs->buf;
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buf_end = buf + msgs->len;
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if ((flags & I2C_MSG_RW_MASK) == I2C_MSG_READ) {
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/* Read */
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while (buf < buf_end) {
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*buf++ = i2c_read_byte(context);
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/* ACK the byte, except for the last one */
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i2c_write_bit(context, buf == buf_end);
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}
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} else {
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/* Write */
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while (buf < buf_end) {
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if (!i2c_write_byte(context, *buf++)) {
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goto finish; /* No ACK received */
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}
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}
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}
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/* Next message */
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msgs++;
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num_msgs--;
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} while (num_msgs);
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/* Complete without error */
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result = 0;
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finish:
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i2c_stop(context);
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return result;
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}
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void i2c_bitbang_init(struct i2c_bitbang *context,
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const struct i2c_bitbang_io *io, void *io_context)
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{
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context->io = io;
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context->io_context = io_context;
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i2c_bitbang_configure(context, I2C_SPEED_STANDARD << I2C_SPEED_SHIFT);
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}
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