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i2c: increase the default clock strech timeout to 250msec.

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This also redefines the timeout in FreeRTOS clock ticks, and implements a two
stage wait: firstly spinning sampling frequently, and then falling back to a
longer wait while sampling less frequently and yielding.
This commit is contained in:
Our Air Quality 2018-06-15 08:22:29 +10:00
parent d9c5f2eaa2
commit c8c7f97290
2 changed files with 42 additions and 23 deletions
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54
extras/i2c/i2c.c
View file

@ -66,7 +66,7 @@ typedef struct i2c_bus_description
bool started;
bool flag;
bool force;
uint32_t clk_stretch;
TickType_t clk_stretch;
} i2c_bus_description_t;
static i2c_bus_description_t i2c_bus[I2C_MAX_BUS];
@ -183,7 +183,7 @@ int i2c_set_frequency_hz(uint8_t bus, uint32_t freq)
return not_ok ? -EINVAL : 0;
}
void i2c_set_clock_stretch(uint8_t bus, uint32_t clk_stretch)
void i2c_set_clock_stretch(uint8_t bus, TickType_t clk_stretch)
{
i2c_bus[bus].clk_stretch = clk_stretch;
}
@ -235,13 +235,46 @@ static inline void clear_sda(uint8_t bus)
#endif
}
static inline void set_scl(uint8_t bus)
#define I2C_CLK_STRETCH_SPIN 1024
static void set_scl(uint8_t bus)
{
#if I2C_USE_GPIO16 == 1
gpio_write(i2c_bus[bus].g_scl_pin, 1);
#else
GPIO.OUT_SET = i2c_bus[bus].g_scl_mask;
#endif
// Clock stretching.
// Spin sampling frequently.
uint32_t clk_stretch_spin = I2C_CLK_STRETCH_SPIN;
do {
if (read_scl(bus)) {
return;
}
clk_stretch_spin--;
} while (clk_stretch_spin);
// Fall back to a longer wait, sampling less frequently.
TickType_t clk_stretch = i2c_bus[bus].clk_stretch;
TickType_t start = xTaskGetTickCount();
do {
vTaskDelay(20 / portTICK_PERIOD_MS);
if (read_scl(bus)) {
return;
}
TickType_t elapsed = xTaskGetTickCount() - start;
if (elapsed > clk_stretch) {
break;
}
} while (1);
debug("bus %u clock stretch timeout", bus);
}
static inline void set_sda(uint8_t bus)
@ -265,10 +298,7 @@ void i2c_start(uint8_t bus)
// Set SDA to 1
set_sda(bus);
i2c_delay(bus);
uint32_t clk_stretch = i2c_bus[bus].clk_stretch;
set_scl(bus);
while (read_scl(bus) == 0 && clk_stretch--)
;
// Repeated start setup time, minimum 4.7us
i2c_delay(bus);
}
@ -286,14 +316,10 @@ void i2c_start(uint8_t bus)
// Output stop condition
bool i2c_stop(uint8_t bus)
{
uint32_t clk_stretch = i2c_bus[bus].clk_stretch;
// Set SDA to 0
clear_sda(bus);
i2c_delay(bus);
// Clock stretching
set_scl(bus);
while (read_scl(bus) == 0 && clk_stretch--)
;
// Stop bit setup time, minimum 4us
i2c_delay(bus);
// SCL is high, set SDA from 0 to 1
@ -315,17 +341,13 @@ bool i2c_stop(uint8_t bus)
// Write a bit to I2C bus
static void i2c_write_bit(uint8_t bus, bool bit)
{
uint32_t clk_stretch = i2c_bus[bus].clk_stretch;
if (bit) {
set_sda(bus);
} else {
clear_sda(bus);
}
i2c_delay(bus);
// Clock stretching
set_scl(bus);
while (read_scl(bus) == 0 && clk_stretch--)
;
// SCL is high, now data is valid
// If SDA is high, check that nobody else is driving SDA
if (bit && read_sda(bus) == 0) {
@ -338,15 +360,11 @@ static void i2c_write_bit(uint8_t bus, bool bit)
// Read a bit from I2C bus
static bool i2c_read_bit(uint8_t bus)
{
uint32_t clk_stretch = i2c_bus[bus].clk_stretch;
bool bit;
// Let the slave drive data
set_sda(bus);
i2c_delay(bus);
set_scl(bus);
// Clock stretching
while (read_scl(bus) == 0 && clk_stretch--)
;
// SCL is high, now data is valid
bit = read_sda(bus);
i2c_delay(bus);