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@@ -2,27 +2,40 @@
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The I2C Master drivers used in QMK have a set of common functions to allow portability between MCUs.
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+## An important note on I2C Addresses
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+
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+All of the addresses expected by this driver should be pushed to the upper 7 bits of the address byte. Setting
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+the lower bit (indicating read/write) will be done by the respective functions. Almost all I2C addresses listed
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+on datasheets and the internet will be represented as 7 bits occupying the lower 7 bits and will need to be
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+shifted to the left (more significant) by one bit. This is easy to do via the bitwise shift operator `<< 1`.
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+
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+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`:
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+
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+`#define MY_I2C_ADDRESS (0x18 << 1)`
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+
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+See https://www.robot-electronics.co.uk/i2c-tutorial for more information about I2C addressing and other technical details.
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+
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## Available functions
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|Function |Description |
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|------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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|`void i2c_init(void);` |Initializes the I2C driver. This function should be called once before any transaction is initiated. |
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-|`uint8_t i2c_start(uint8_t address, uint16_t timeout);` |Starts an I2C transaction. Address is the 7-bit slave address without the direction bit. |
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-|`uint8_t i2c_transmit(uint8_t address, uint8_t* data, uint16_t length, uint16_t timeout);` |Transmit data over I2C. Address is the 7-bit slave address without the direction. Returns status of transaction. |
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-|`uint8_t i2c_receive(uint8_t address, uint8_t* data, uint16_t length, uint16_t timeout);` |Receive data over I2C. Address is the 7-bit slave address without the direction. Saves number of bytes specified by `length` in `data` array. Returns status of transaction. |
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-|`uint8_t i2c_writeReg(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout);` |Same as the `i2c_transmit` function but `regaddr` sets where in the slave the data will be written. |
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-|`uint8_t i2c_readReg(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout);` |Same as the `i2c_receive` function but `regaddr` sets from where in the slave the data will be read. |
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-|`uint8_t i2c_stop(void);` |Ends an I2C transaction. |
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+|`i2c_status_t i2c_start(uint8_t address, uint16_t timeout);` |Starts an I2C transaction. Address is the 7-bit slave address without the direction bit. |
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+|`i2c_status_t i2c_transmit(uint8_t address, uint8_t* data, uint16_t length, uint16_t timeout);` |Transmit data over I2C. Address is the 7-bit slave address without the direction. Returns status of transaction. |
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+|`i2c_status_t i2c_receive(uint8_t address, uint8_t* data, uint16_t length, uint16_t timeout);` |Receive data over I2C. Address is the 7-bit slave address without the direction. Saves number of bytes specified by `length` in `data` array. Returns status of transaction. |
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+|`i2c_status_t i2c_writeReg(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout);` |Same as the `i2c_transmit` function but `regaddr` sets where in the slave the data will be written. |
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+|`i2c_status_t i2c_readReg(uint8_t devaddr, uint8_t regaddr, uint8_t* data, uint16_t length, uint16_t timeout);` |Same as the `i2c_receive` function but `regaddr` sets from where in the slave the data will be read. |
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+|`i2c_status_t i2c_stop(void);` |Ends an I2C transaction. |
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### Function Return
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All the above functions, except `void i2c_init(void);` return the following truth table:
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-|Return Value |Description |
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-|---------------|---------------------------------------------------|
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-|0 |Operation executed successfully. |
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-|-1 |Operation failed. |
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-|-2 |Operation timed out. |
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+|Return Constant |Value|Description |
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+|--------------------|-----|--------------------------------|
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+|`I2C_STATUS_SUCCESS`|0 |Operation executed successfully.|
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+|`I2C_STATUS_ERROR` |-1 |Operation failed. |
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+|`I2C_STATUS_TIMEOUT`|-2 |Operation timed out. |
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## AVR
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