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:
  • ESP8266 Arduino Core 2.1.0 up to 2.7.4
  • There is currently an issue with ESP8266 Arduino Core 3, i.e. it won't compile #44
• Tested Native SDK versions:
  • SDK Version 3.0.1
  • 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.

NOTE for AM2320 Sensor: The wake-up sequence is not compatible with brzo_i2c, see analysis here

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".

Disabling or enabling Interrupts during i2c reads or writes

In brzo_i2c.h you can set the behaviour how interrupts during i2c reads or writes are handled: Setting BRZO_I2C_DISABLE_INTERRUPTS to 1 will disable all interrupts during i2c read or writes. The default is all interrupts are disabled. For further information about disabling or enabling interrupts refer to the wiki

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, i.e. either SDA or SCL is low
  • 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...
}