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i2c: use open drain for output rather than flipping between input and output.

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This commit is contained in:
ourairquality 2016-09-01 21:18:09 +10:00
parent 7041c014bb
commit e6eda5c3ff
1 changed files with 16 additions and 17 deletions
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33
extras/i2c/i2c.c
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@ -49,48 +49,47 @@ void i2c_init(uint8_t scl_pin, uint8_t sda_pin)
gpio_set_pullup(g_scl_pin, 1, 1);
gpio_set_pullup(g_sda_pin, 1, 1);
// I2C bus idle state.
gpio_enable(g_scl_pin, GPIO_INPUT);
gpio_enable(g_scl_pin, GPIO_INPUT);
gpio_enable(g_scl_pin, GPIO_OUT_OPEN_DRAIN);
gpio_enable(g_sda_pin, GPIO_OUT_OPEN_DRAIN);
// Set the pins to a low output state for when they are configured
// as outputs.
gpio_write(g_scl_pin, 0);
gpio_write(g_sda_pin, 0);
// I2C bus idle state.
gpio_write(g_scl_pin, 1);
gpio_write(g_sda_pin, 1);
}
static void i2c_delay(void)
static inline void i2c_delay(void)
{
sdk_os_delay_us(CLK_HALF_PERIOD_US);
}
// Set SCL as input, allowing it to float high, and return current
// level of line, 0 or 1
static bool read_scl(void)
static inline bool read_scl(void)
{
gpio_enable(g_scl_pin, GPIO_INPUT);
gpio_write(g_scl_pin, 1);
return gpio_read(g_scl_pin); // Clock high, valid ACK
}
// Set SDA as input and return current level of line, 0 or 1
static bool read_sda(void)
// Set SDA as input, allowing it to float high, and return current
// level of line, 0 or 1
static inline bool read_sda(void)
{
gpio_enable(g_sda_pin, GPIO_INPUT);
gpio_write(g_sda_pin, 1);
// TODO: Without this delay we get arbitration lost in i2c_stop
i2c_delay();
return gpio_read(g_sda_pin); // Clock high, valid ACK
}
// Actively drive SCL signal low
static void clear_scl(void)
static inline void clear_scl(void)
{
gpio_enable(g_scl_pin, GPIO_OUT_OPEN_DRAIN);
gpio_write(g_scl_pin, 0);
}
// Actively drive SDA signal low
static void clear_sda(void)
static inline void clear_sda(void)
{
gpio_enable(g_sda_pin, GPIO_OUT_OPEN_DRAIN);
gpio_write(g_sda_pin, 0);
}
// Output start condition