From c8c7f972900e573ae2f05fffc93b7421afeffa09 Mon Sep 17 00:00:00 2001
From: Our Air Quality <info@ourairquality.org>
Date: Fri, 15 Jun 2018 08:22:29 +1000
Subject: [PATCH] i2c: increase the default clock strech timeout to 250msec.
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.
---
extras/i2c/i2c.c | 54 ++++++++++++++++++++++++++++++++----------------
extras/i2c/i2c.h | 11 +++++-----
2 files changed, 42 insertions(+), 23 deletions(-)
diff --git a/extras/i2c/i2c.c b/extras/i2c/i2c.c
index 204bc98..faa245a 100644
--- a/extras/i2c/i2c.c
+++ b/extras/i2c/i2c.c
@@ -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);
diff --git a/extras/i2c/i2c.h b/extras/i2c/i2c.h
index 46f8468..9cd55f2 100644
--- a/extras/i2c/i2c.h
+++ b/extras/i2c/i2c.h
@@ -32,6 +32,8 @@
#include <stdint.h>
#include <stdbool.h>
#include <errno.h>
+#include <FreeRTOS.h>
+#include <task.h>
#ifdef __cplusplus
extern "C" {
@@ -51,7 +53,8 @@ extern "C" {
#define I2C_USE_GPIO16 0
#endif
-#define I2C_DEFAULT_CLK_STRETCH (10)
+/* Default clock strech waiting time, 250 msec. */
+#define I2C_DEFAULT_CLK_STRETCH (250 / portTICK_PERIOD_MS)
/* SCL speed settings. 160 MHz sysclk frequency will result in improved
* timing accuracy. Greater bitrates will have poorer accuracy. 1000K is the
@@ -86,7 +89,6 @@ typedef struct i2c_dev
* @param scl_pin SCL pin for I2C
* @param sda_pin SDA pin for I2C
* @param freq frequency of bus (ex : I2C_FREQ_400K)
- * @param clk_stretch I2C clock stretch. I2C_DEFAULT_CLK_STRETCH would be good in most cases
* @return Non-zero if error occured
*/
int i2c_init(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, i2c_freq_t freq);
@@ -97,7 +99,6 @@ int i2c_init(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, i2c_freq_t freq);
* @param scl_pin SCL pin for I2C
* @param sda_pin SDA pin for I2C
* @param freq frequency of bus in hertz
- * @param clk_stretch I2C clock stretch. I2C_DEFAULT_CLK_STRETCH would be good in most cases
* @return Non-zero if error occured
*/
int i2c_init_hz(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, uint32_t freq);
@@ -119,9 +120,9 @@ int i2c_set_frequency_hz(uint8_t bus, uint32_t freq);
/**
* Change clock stretch
* @param bus I2C bus
- * @param clk_stretch I2C clock stretch. I2C_DEFAULT_CLK_STRETCH by default
+ * @param clk_stretch I2C clock stretch, in ticks. I2C_DEFAULT_CLK_STRETCH by default
*/
-void i2c_set_clock_stretch(uint8_t bus, uint32_t clk_stretch);
+void i2c_set_clock_stretch(uint8_t bus, TickType_t clk_stretch);
/**
* Write a byte to I2C bus.