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| author | brickbots <rich@brickbots.com> | 2020-03-15 00:17:48 -0700 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2020-03-15 00:17:48 -0700 |
| commit | 499d7c8ce610a3c150c64eaacbca3038f7796cc5 (patch) | |
| tree | 729e82225170a337d9007b46e7d7708f480f8da8 /docs | |
| parent | 60b020acabf5f78976203213bfd0097eed7656a4 (diff) | |
| download | qmk_firmware-499d7c8ce610a3c150c64eaacbca3038f7796cc5.tar.gz qmk_firmware-499d7c8ce610a3c150c64eaacbca3038f7796cc5.zip | |
[Docs] Update to I2C docs: Clarify address expectation and return values (#8413)
* Clarifying docs for i2c
* Fix typo
* Fix up punctuation
* Implementing great suggestions
* Update docs/i2c_driver.md
* Update docs/i2c_driver.md
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/i2c_driver.md | 35 |
1 files changed, 24 insertions, 11 deletions
diff --git a/docs/i2c_driver.md b/docs/i2c_driver.md index d5c340edce..c9f53ef0d6 100644 --- a/docs/i2c_driver.md +++ b/docs/i2c_driver.md @@ -2,27 +2,40 @@ The I2C Master drivers used in QMK have a set of common functions to allow portability between MCUs. +## An important 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`: + +`#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. + ## Available functions |Function |Description | |------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------| |`void i2c_init(void);` |Initializes the I2C driver. This function should be called once before any transaction is initiated. | -|`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. | -|`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. | -|`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. | -|`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. | -|`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. | -|`uint8_t i2c_stop(void);` |Ends an I2C transaction. | +|`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. | +|`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. | +|`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. | +|`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. | +|`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. | +|`i2c_status_t i2c_stop(void);` |Ends an I2C transaction. | ### Function Return All the above functions, except `void i2c_init(void);` return the following truth table: -|Return Value |Description | -|---------------|---------------------------------------------------| -|0 |Operation executed successfully. | -|-1 |Operation failed. | -|-2 |Operation timed out. | +|Return Constant |Value|Description | +|--------------------|-----|--------------------------------| +|`I2C_STATUS_SUCCESS`|0 |Operation executed successfully.| +|`I2C_STATUS_ERROR` |-1 |Operation failed. | +|`I2C_STATUS_TIMEOUT`|-2 |Operation timed out. | ## AVR |