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Brzo I2C

Brzo i2c implements an i2c master and is written in assembly language for the esp8266. The core features are:

  • Fast mode plus speeds
    • 800 KHz @ 80 MHz CPU frequency
    • 1 MHz @ 160 MHz CPU frequency
  • Precise timing for SCL and SDA, including removal of spikes
  • i2c transactions: Group any combination of i2c writes or reads together, either with or without repeated start.

For further information you may refer to the wiki

HW and Tool Chain Support

  • Brzo i2c supports only esp8266 modules because it is implented in Xtensa assembly language.
  • The code is tested for the Arduino tool chain
  • And thanks to valkuc it works for the native tool chain, too! Make sure to use the correct compiler flags.
  • Tested Arduino versions:
    • Arduino IDE 1.6.8, ESP8266 Arduino Core 2.2.0
    • Arduino IDE 1.6.5, ESP8266 Arduino Core 2.1.0
  • Tested Native SDK versions:
    • SDK Version 2.0.0

Brzo i2c was tested with several i2c devices. If you find one which is not working, please open an issue.

How to install the Brzo I2C Library

  • Use the Library Manager:

    • If you are using the ArduinoIDE, you can install via library manager
    • If you are developing with PlatformIO then simply use the library manager to install brzo_i2c

  • Pull it from github

And then just include brzo_i2c in your sketch as any other library with #include "brzo_i2c.h".

I2C Setup

To setup the i2c bus you need to call at least once brzo_i2c_setup.

brzo_i2c_setup(uint8_t sda, uint8_t scl, uint32_t clock_stretch_time_out_usec).
Input

  • The number of your SDA Pin
  • The number of your SCL Pin
  • The timeout for an i2c slave clock stretch in micro seconds. Be careful when using i2c devices with a very long clock stretching, please read the wiki.

Returns

  • None

Example: brzo_i2c_setup(5, 12, 200);

I2C Transactions

The motivation for i2c transactions is found on the wiki. An i2c transactions always begins with brzo_i2c_start_transaction and ends with brzo_i2c_end_transaction. Within a transaction you can combine any number i2c commands with or without a repeated start, i.e. brzo_i2c_write or brzo_i2c_read. A transaction is bound to one i2c slave and all commands are executed at the same SCL speed. Thus, brzo_i2c_start_transaction takes the slave address and SCL speed in KHz as input parameters.

Begin a transaction

brzo_i2c_start_transaction(uint8_t slave_address, uint16_t SCL_frequency_KHz)

Input

  • I2c slave address (7 bit encoded)
  • SCL speed to be used for the entire transaction in KHz (SCL speed is rounded to the next 100-level, e.g., 651 will be rounded up to 700)

Returns

  • None

Example: Start a transaction to an i2c slave at 0x20 with 1 MHz SCL speed. brzo_i2c_start_transaction(0x20, 1000);

End a Transaction

uint8_t brzo_i2c_end_transaction()

Note:

  • The last i2c command before calling brzo_i2c_end_transaction() must not contain a repeated start, therefore use brzo_i2c_read/write(.., .., false) to send a STOP sequence instead of another repeated START.
  • Refer to the i2c specification about repeated starts and how to "end" them

Input

  • None

Returns

  • 0 : All i2c commands were executed without errors
  • errors
    • 1 : Bus not free
    • 2 : Not ACK ("NACK") by slave during write: Either the slave did not respond to the given slave address; or the slave did not ACK a byte transferred by the master.
    • 4 : Not ACK ("NACK") by slave during read, i.e. slave did not respond to the given slave address
    • 8 : Clock Stretching by slave exceeded maximum clock stretching time. Most probably, there is a bus stall now!
    • 16 : Read was called with 0 bytes to be read by the master. Command not sent to the slave, since this could yield to a bus stall
    • 32 : ACK Polling timeout exceeded

I2C Commands

The following i2c commands shall only be used within a transaction!

I2C write

brzo_i2c_write(uint8_t *data, uint8_t no_of_bytes, boolean repeated_start)

Note:

  • You can only call brzo_i2c_write inside a transaction!
  • Of course, there is error checking inside the write command. However, errors are only reported at the end of a transaction.

Input

  • A pointer to an array of bytes: Either use the base address, e.g., brzo_i2c_write(buffer, 2, ..) or use the address of a specific array element, e.g. brzo_i2c_write(&buffer[4], 2, ..);. The former writes buffer[0] and buffer[1], the latter buffer[4] and buffer[5]
  • The number of bytes to be written
  • Repeated start if needed

Returns

  • None

Example

  • From (the previously defined) uint8_t buffer[4] write 2 bytes (buffer[0], buffer[1]) and finish the command with a STOP, i.e. no repeated start. brzo_i2c_write(buffer, 2, false);

I2C Read

brzo_i2c_read(uint8_t *data, uint8_t no_of_bytes, boolean repeated_start)

Note:

  • You can only call brzo_i2c_read inside a transaction!
  • Of course, there is error checking inside the read command. However, errors are only reported at the end of a transaction.

Input

  • A pointer to an array of bytes: Either use the base address, e.g., brzo_i2c_read(buffer, 2, ..) or use the address of a specific array element, e.g. brzo_i2c_read(&buffer[4], 2, ..);. The former receives two bytes and saves them to buffer[0] and buffer[1], the latter to buffer[4] and buffer[5]
  • The number of bytes to be read
  • Repeated start if needed

Returns

  • None

Example

  • Into (the previously defined) uint8_t buffer[4] store 3 bytes (buffer[0], buffer[1], buffer[2]) and finish the read with a repeated start, i.e. do not send a STOP. brzo_i2c_read(buffer, 3, true);

I2C Acknowledge Polling

Please see the wiki for further information about ACK Polling.

brzo_i2c_ACK_polling(uint16_t ACK_polling_time_out_usec)

Note:

  • You can only call brzo_i2c_ACK_polling inside a transaction!
  • There is error checking inside the ACK polling command. However, errors are only reported at the end of a transaction.

Input

  • The timeout for ACK polling in micro seconds

Returns

  • None

Example

  • Perform an ACK polling with 10 msec timeout brzo_i2c_ACK_polling(10000)

Example of I2C Transactions

Examples of sketches are located in /examples folder.

#include "brzo_i2c.h"

uint8_t SDA_PIN = 5;
uint8_t SCL_PIN = 12;
uint8_t ADT7420_ADR = 0x49;
uint8_t buffer[3];
uint8_t return_code = 0;
uint32_t ADC_code = 0;
long temp;

void setup() {
  // Setup i2c with clock stretching timeout of 2000 usec
  brzo_i2c_setup(SDA_PIN, SCL_PIN, 2000);
...
}

...

// Start a transaction to the ADT7420 at 400 KHz

brzo_i2c_start_transaction(ADT7420_ADR, 400);
  buffer[0] = 0x03; // select configuration register
  buffer[1] = 0xA0; // select 16 bit resolution
  brzo_i2c_write(buffer, 2, false); // Write two bytes with no repeated start
  buffer[0] = 0x00; // select temperature register
  brzo_i2c_write(buffer, 1, true); // Write one byte WITH repeated start
  brzo_i2c_read(buffer, 2, false); // Read temperature, two bytes
return_code = brzo_i2c_end_transaction();

if (return_code == 0) {
  ADC_code = ((buffer[0] << 8) | buffer[1]);
  temp = ADC_code / 128.0;
 }
else {
  // Error Handling here...
}