From a2e6cb94c6b4e731ae621f3ba8020f8e0de65bf6 Mon Sep 17 00:00:00 2001
From: Dimitris Mantzouranis <d3xter93@gmail.com>
Date: Mon, 29 May 2023 20:36:51 +0300
Subject: [PATCH] i2c master: add i2c fallback support

---
 docs/i2c_driver.md                     | 25 +++++++++++++++++++++
 platforms/chibios/drivers/i2c_master.c | 31 +++++++++++++++++++++++++-
 2 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/docs/i2c_driver.md b/docs/i2c_driver.md
index faff0a1d7bf..2efce83efe8 100644
--- a/docs/i2c_driver.md
+++ b/docs/i2c_driver.md
@@ -117,6 +117,31 @@ See [this page](https://www.playembedded.org/blog/stm32-i2c-chibios/#8_I2Cv2_I2C
 |`I2C1_TIMINGR_SCLH`  |`38U`  |
 |`I2C1_TIMINGR_SCLL`  |`129U` |
 
+### I2C Fallback :id=arm-configuration-i2cfallback
+
+ChibiOS provides a software solution through the I2C Fallback driver for cases where hardware I2C is not available.
+To enable it, modify your board's `halconf.h` to enable the first I2C Fallback driver( assuming selected I2C peripheral is `I2CD1`).
+```c
+#define SW_I2C_USE_I2C1
+```
+By default, the delay required for I2C communication is calculated automatically with a target frequency of 100kHz, through the ChibiOS OSAL layer. If you wish to override this behavior, further modify your board's `halconf.h`
+```c
+#define SW_I2C_USE_OSAL_DELAY FALSE
+```
+and provide the following function in your board's files
+```c
+void i2c_sw_delay(void) {
+  // custom delay goes here
+}
+```
+The I2C Fallback configuration structure is as follows
+|`config.h` Override    |Default |
+|-----------------------|--------|
+|`I2C_CLOCK_FREQUENCY`  |`100000`|
+|`SW_I2C_USE_OSAL_DELAY`|`TRUE`  |
+
+Note that `I2C_CLOCK_FREQUENCY` is target I2C speed in `Hz` and is only respected if `SW_I2C_USE_OSAL_DELAY` is `TRUE`.
+
 ## API :id=api
 
 ### `void i2c_init(void)` :id=api-i2c-init
diff --git a/platforms/chibios/drivers/i2c_master.c b/platforms/chibios/drivers/i2c_master.c
index 7c49f9d0059..ad149d45407 100644
--- a/platforms/chibios/drivers/i2c_master.c
+++ b/platforms/chibios/drivers/i2c_master.c
@@ -90,10 +90,39 @@
 #    endif
 #endif
 
+#ifdef SW_I2C_USE_I2C1
+#    ifndef I2C1_SCL_PAL_MODE
+#        define I2C1_SCL_PAL_MODE PAL_MODE_ALTERNATE_OPENDRAIN
+#    endif
+#    ifndef I2C1_SDA_PAL_MODE
+#        define I2C1_SDA_PAL_MODE PAL_MODE_ALTERNATE_OPENDRAIN
+#    endif
+#    ifndef I2C_CLOCK_FREQUENCY
+#        define I2C_CLOCK_FREQUENCY 100000
+#    endif
+#    ifndef SW_I2C_DELAY
+#        define SW_I2C_DELAY ceil((CH_CFG_ST_FREQUENCY / I2C_CLOCK_FREQUENCY) / 2)
+#    endif
+#    ifndef SW_I2C_USE_OSAL_DELAY
+#        define SW_I2C_USE_OSAL_DELAY TRUE
+#    endif
+#    if (SW_I2C_USE_OSAL_DELAY == FALSE)
+__attribute__((weak)) void i2c_sw_delay(void) {}
+#    endif
+#endif
 static uint8_t i2c_address;
 
 static const I2CConfig i2cconfig = {
-#if defined(USE_I2CV1_CONTRIB)
+#if defined(SW_I2C_USE_I2C1)
+    0,
+    I2C1_SCL_PIN,
+    I2C1_SDA_PIN,
+#    if (SW_I2C_USE_OSAL_DELAY == FALSE)
+    &i2c_sw_delay,
+#    else
+    SW_I2C_DELAY,
+#    endif
+#elif defined(USE_I2CV1_CONTRIB)
     I2C1_CLOCK_SPEED,
 #elif defined(USE_I2CV1)
     I2C1_OPMODE,