Khepera III Toolbox/The Toolbox/Modules/i2c stream

The i2c_stream module implements a simple I2C data streaming protocol. The device from which data is streamed must implement that same protocol as well.

Synopsis edit

Check out the source code of the i2c_stream_read program for an example.

Description edit

This module uses the i2cal module to transfer data blocks from the external device (chip) to the program. It basically consists of two functions:

  • i2c_stream_read_start, to start streaming
  • i2c_stream_read_next, which has to be called frequently (and in more or less regular intervals) to read the available data blocks

The following four settings need to be provided to the module

  • device: the I2C address of the device to query
  • reg: the I2C register from which the stream is read
  • block_size: the size of one block (in bytes)
  • block_count_max: the maximum number of blocks to transfer at once (this value must be <= 128 / block_size)

Streaming Protocol edit

The protocol used for data streaming is very simple: To reset the stream, the module first sends the register followed by a 1. To read a chunk, the module sends the register and then reads a multiple of (block_size + 1) bytes from the device. The first byte of a block is a status byte which can take one of the following values:

  • 255 (I2C_STREAM_BUFFER_OVERRUN): A buffer overrun occurred on the device, i.e. the blocks were not read fast enough.
  • 254 (I2C_STREAM_EMPTY): The block does not contain any data.
  • 0..253: the available number of blocks on the device