1 files changed, 290 insertions, 0 deletions

diff --git a/docs/drivers/i2c.md b/docs/drivers/i2c.md
new file mode 100644
index 0000000000..10949ed59e
--- /dev/null
+++ b/docs/drivers/i2c.md
@@ -0,0 +1,290 @@
+# I2C Master Driver {#i2c-master-driver}
+
+The I2C Master drivers used in QMK have a set of common functions to allow portability between MCUs.
+
+## Usage {#usage}
+
+In most cases, the I2C Master driver code is automatically included if you are using a feature or driver which requires it, such as [OLED](../features/oled_driver).
+
+However, if you need to use the driver standalone, add the following to your `rules.mk`:
+
+```make
+I2C_DRIVER_REQUIRED = yes
+```
+
+You can then call the I2C API by including `i2c_master.h` in your code.
+
+## I2C Addressing {#note-on-i2c-addresses}
+
+All of the addresses expected by this driver should be pushed to the upper 7 bits of the address byte. Setting
+the lower bit (indicating read/write) will be done by the respective functions. Almost all I2C addresses listed 
+on datasheets and the internet will be represented as 7 bits occupying the lower 7 bits and will need to be
+shifted to the left (more significant) by one bit. This is easy to do via the bitwise shift operator `<< 1`.
+
+You can either do this on each call to the functions below, or once in your definition of the address. For example, if your device has an address of `0x18`:
+
+```c
+#define MY_I2C_ADDRESS (0x18 << 1)
+```
+
+See https://www.robot-electronics.co.uk/i2c-tutorial for more information about I2C addressing and other technical details.
+
+## AVR Configuration {#avr-configuration}
+
+The following defines can be used to configure the I2C master driver:
+
+|`config.h` Override|Description          |Default |
+|-------------------|---------------------|--------|
+|`F_SCL`            |Clock frequency in Hz|`400000`|
+
+No further setup is required - just connect the `SDA` and `SCL` pins of your I2C devices to the matching pins on the MCU:
+
+|MCU               |`SCL`|`SDA`|
+|------------------|-----|-----|
+|ATmega16/32U4     |`D0` |`D1` |
+|AT90USB64/128     |`D0` |`D1` |
+|ATmega32A         |`C0` |`C1` |
+|ATmega328/P       |`C5` |`C4` |
+
+::: tip
+The ATmega16/32U2 does not possess I2C functionality, and so cannot use this driver.
+:::
+
+## ChibiOS/ARM Configuration {#arm-configuration}
+
+You'll need to determine which pins can be used for I2C -- a an example, STM32 parts generally have multiple I2C peripherals, labeled I2C1, I2C2, I2C3 etc.
+
+To enable I2C, modify your board's `halconf.h` to enable I2C:
+
+```c
+#define HAL_USE_I2C TRUE
+```
+
+Then, modify your board's `mcuconf.h` to enable the peripheral you've chosen, for example:
+
+```c
+#undef STM32_I2C_USE_I2C2
+#define STM32_I2C_USE_I2C2 TRUE
+```
+
+|`mcuconf.h` Setting         |Description                                                                       |Default|
+|----------------------------|----------------------------------------------------------------------------------|-------|
+|`STM32_I2C_BUSY_TIMEOUT`    |Time in milliseconds until the I2C command is aborted if no response is received  |`50`   |
+|`STM32_I2C_XXX_IRQ_PRIORITY`|Interrupt priority for hardware driver XXX (THIS IS AN EXPERT SETTING)            |`10`   |
+|`STM32_I2C_USE_DMA`         |Enable/Disable the ability of the MCU to offload the data transfer to the DMA unit|`TRUE` |
+|`STM32_I2C_XXX_DMA_PRIORITY`|Priority of DMA unit for hardware driver XXX (THIS IS AN EXPERT SETTING)          |`1`    |
+
+Configuration-wise, you'll need to set up the peripheral as per your MCU's datasheet -- the defaults match the pins for a Proton-C, i.e. STM32F303.
+
+|`config.h` Overrride    |Description                                                   |Default|
+|------------------------|--------------------------------------------------------------|-------|
+|`I2C_DRIVER`            |I2C peripheral to use - I2C1 -> `I2CD1`, I2C2 -> `I2CD2` etc. |`I2CD1`|
+|`I2C1_SCL_PIN`          |The pin definition for SCL                                    |`B6`   |
+|`I2C1_SCL_PAL_MODE`     |The alternate function mode for SCL                           |`4`    |
+|`I2C1_SDA_PIN`          |The pin definition for SDA                                    |`B7`   |
+|`I2C1_SDA_PAL_MODE`     |The alternate function mode for SDA                           |`4`    |
+
+The following configuration values depend on the specific MCU in use.
+
+### I2Cv1 {#arm-configuration-i2cv1}
+
+* STM32F1xx
+* STM32F2xx
+* STM32F4xx
+* STM32L0xx
+* STM32L1xx
+
+See [this page](https://www.playembedded.org/blog/stm32-i2c-chibios/#7_I2Cv1_configuration_structure) for the I2Cv1 configuration structure.
+
+|`config.h` Override|Default         |
+|-------------------|----------------|
+|`I2C1_OPMODE`      |`OPMODE_I2C`    |
+|`I2C1_CLOCK_SPEED` |`100000`        |
+|`I2C1_DUTY_CYCLE`  |`STD_DUTY_CYCLE`|
+
+### I2Cv2 {#arm-configuration-i2cv2}
+
+* STM32F0xx
+* STM32F3xx
+* STM32F7xx
+* STM32L4xx
+
+See [this page](https://www.playembedded.org/blog/stm32-i2c-chibios/#8_I2Cv2_I2Cv3_configuration_structure) for the I2Cv2 configuration structure.
+
+|`config.h` Override  |Default|
+|---------------------|-------|
+|`I2C1_TIMINGR_PRESC` |`0U`   |
+|`I2C1_TIMINGR_SCLDEL`|`7U`   |
+|`I2C1_TIMINGR_SDADEL`|`0U`   |
+|`I2C1_TIMINGR_SCLH`  |`38U`  |
+|`I2C1_TIMINGR_SCLL`  |`129U` |
+
+## API {#api}
+
+### `void i2c_init(void)` {#api-i2c-init}
+
+Initialize the I2C driver. This function must be called only once, before any of the below functions can be called.
+
+This function is weakly defined, meaning it can be overridden if necessary for your particular use case:
+
+```c
+void i2c_init(void) {
+    gpio_set_pin_input(B6); // Try releasing special pins for a short time
+    gpio_set_pin_input(B7);
+    wait_ms(10); // Wait for the release to happen
+
+    palSetPadMode(GPIOB, 6, PAL_MODE_ALTERNATE(4) | PAL_STM32_OTYPE_OPENDRAIN | PAL_STM32_PUPDR_PULLUP); // Set B6 to I2C function
+    palSetPadMode(GPIOB, 7, PAL_MODE_ALTERNATE(4) | PAL_STM32_OTYPE_OPENDRAIN | PAL_STM32_PUPDR_PULLUP); // Set B7 to I2C function
+}
+```
+
+---
+
+### `i2c_status_t i2c_transmit(uint8_t address, uint8_t *data, uint16_t length, uint16_t timeout)` {#api-i2c-transmit}
+
+Send multiple bytes to the selected I2C device.
+
+#### Arguments {#api-i2c-transmit-arguments}
+
+ - `uint8_t address`  
+   The 7-bit I2C address of the device.
+ - `uint8_t *data`  
+   A pointer to the data to transmit.
+ - `uint16_t length`  
+ The number of bytes to write. Take care not to overrun the length of `data`.
+ - `uint16_t timeout`  
+   The time in milliseconds to wait for a response from the target device.
+
+#### Return Value {#api-i2c-transmit-return}
+
+`I2C_STATUS_TIMEOUT` if the timeout period elapses, `I2C_STATUS_ERROR` if some other error occurs, otherwise `I2C_STATUS_SUCCESS`.
+
+---
+
+### `i2c_status_t i2c_receive(uint8_t address, uint8_t* data, uint16_t length, uint16_t timeout)` {#api-i2c-receive}
+
+Receive multiple bytes from the selected I2C device.
+
+#### Arguments {#api-i2c-receive-arguments}
+
+ - `uint8_t address`  
+   The 7-bit I2C address of the device.
+ - `uint8_t *data`  
+   A pointer to the buffer to read into.
+ - `uint16_t length`  
+ The number of bytes to read. Take care not to overrun the length of `data`.
+ - `uint16_t timeout`  
+   The time in milliseconds to wait for a response from the target device.
+
+#### Return Value {#api-i2c-receive-return}
+
+`I2C_STATUS_TIMEOUT` if the timeout period elapses, `I2C_STATUS_ERROR` if some other error occurs, otherwise `I2C_STATUS_SUCCESS`.
+
+---
+
+### `i2c_status_t i2c_write_register(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout)` {#api-i2c-write-register}
+
+Writes to a register with an 8-bit address on the I2C device.
+
+#### Arguments {#api-i2c-write-register-arguments}
+
+ - `uint8_t devaddr`  
+   The 7-bit I2C address of the device.
+ - `uint8_t regaddr`  
+   The register address to write to.
+ - `uint8_t *data`  
+   A pointer to the data to transmit.
+ - `uint16_t length`  
+ The number of bytes to write. Take care not to overrun the length of `data`.
+ - `uint16_t timeout`  
+   The time in milliseconds to wait for a response from the target device.
+
+#### Return Value {#api-i2c-write-register-return}
+
+`I2C_STATUS_TIMEOUT` if the timeout period elapses, `I2C_STATUS_ERROR` if some other error occurs, otherwise `I2C_STATUS_SUCCESS`.
+
+---
+
+### `i2c_status_t i2c_write_register16(uint8_t devaddr, uint16_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout)` {#api-i2c-write-register16}
+
+Writes to a register with a 16-bit address (big endian) on the I2C device.
+
+#### Arguments {#api-i2c-write-register16-arguments}
+
+ - `uint8_t devaddr`  
+   The 7-bit I2C address of the device.
+ - `uint16_t regaddr`  
+   The register address to write to.
+ - `uint8_t *data`  
+   A pointer to the data to transmit.
+ - `uint16_t length`  
+ The number of bytes to write. Take care not to overrun the length of `data`.
+ - `uint16_t timeout`  
+   The time in milliseconds to wait for a response from the target device.
+
+#### Return Value {#api-i2c-write-register16-return}
+
+`I2C_STATUS_TIMEOUT` if the timeout period elapses, `I2C_STATUS_ERROR` if some other error occurs, otherwise `I2C_STATUS_SUCCESS`.
+
+---
+
+### `i2c_status_t i2c_read_register(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout)` {#api-i2c-read-register}
+
+Reads from a register with an 8-bit address on the I2C device.
+
+#### Arguments {#api-i2c-read-register-arguments}
+
+ - `uint8_t devaddr`  
+   The 7-bit I2C address of the device.
+ - `uint8_t regaddr`  
+   The register address to read from.
+ - `uint16_t length`  
+ The number of bytes to read. Take care not to overrun the length of `data`.
+ - `uint16_t timeout`  
+   The time in milliseconds to wait for a response from the target device.
+
+#### Return Value {#api-i2c-read-register-return}
+
+`I2C_STATUS_TIMEOUT` if the timeout period elapses, `I2C_STATUS_ERROR` if some other error occurs, otherwise `I2C_STATUS_SUCCESS`.
+
+---
+
+### `i2c_status_t i2c_read_register16(uint8_t devaddr, uint16_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout)` {#api-i2c-read-register16}
+
+Reads from a register with a 16-bit address (big endian) on the I2C device.
+
+#### Arguments {#api-i2c-read-register16-arguments}
+
+ - `uint8_t devaddr`  
+   The 7-bit I2C address of the device.
+ - `uint16_t regaddr`  
+   The register address to read from.
+ - `uint16_t length`  
+ The number of bytes to read. Take care not to overrun the length of `data`.
+ - `uint16_t timeout`  
+   The time in milliseconds to wait for a response from the target device.
+
+#### Return Value {#api-i2c-read-register16-return}
+
+`I2C_STATUS_TIMEOUT` if the timeout period elapses, `I2C_STATUS_ERROR` if some other error occurs, otherwise `I2C_STATUS_SUCCESS`.
+
+---
+
+### `i2c_status_t i2c_ping_address(uint8_t address, uint16_t timeout)` {#api-i2c-ping-address}
+
+Pings the I2C bus for a specific address. 
+
+On ChibiOS a "best effort" attempt is made by reading a single byte from register 0 at the requested address. This should generally work except for I2C devices that do not not respond to a register 0 read request, which will result in a false negative result (unsucessful response to ping attempt).
+
+This function is weakly defined, meaning it can be overridden if necessary for your particular use case:
+
+#### Arguments
+
+ - `uint8_t address`  
+   The 7-bit I2C address of the device (ie. without the read/write bit - this will be set automatically).
+ - `uint16_t timeout`  
+   The time in milliseconds to wait for a response from the target device.
+
+#### Return Value
+
+`I2C_STATUS_TIMEOUT` if the timeout period elapses, `I2C_STATUS_ERROR` if some other error occurs, otherwise `I2C_STATUS_SUCCESS`.