Write Channel#

  • Data alignment : 8 bits

  • Channel type : Stream

  • Direction : Write

The write channel provides high bandwidth communication from the host computer to the controller, and is used to send data to the devices.

Data is sent as a sequence of Data Frames with their Common_Timestamp field set to 0. Multiple device samples can be sent in a single write frame. In this case, the Sample_Size field will be equal to the Write_Sample_Size multiplied by the number of sent samples.

A compliant implementation of this channel requires the following:

  • The controller MUST accept all frames sent by the host, at any rate that does not exceed the maximal channel bandwidth, which will be implementation-defined.

  • The controller MUST send all frames received to the destination devices in the same order it receives frames from the computer

  • Devices that accept data from the write channel MAY buffer it. A device’s Device Datasheet MUST specify if data is buffered and if there is any possibility of dropping frames (e.g: receiving a frame while one is being processed)

  • Devices that accept data from the write channel MAY inform the host about their internal state so a host application can adjust the production rate of write frames accordingly. If used, this mechanism MUST use existing channels (e.g. Register or Read channels), MUST NOT directly affect the operation of the Write channel and MUST be described on the Device Datasheet.

In summary, the Write Channel’s sole responsibility is passing frames to devices. The Write channel is not required to provide any auxiliary signals about its internal state, specific frame delivery timestamps or any other operational details.

Write Word Alignment#

Hardware implementations of controllers might require a word size greater than 8 bits. In this case the host MUST add after every frame transmission, single- or multi-sample, as many padding bytes with the value 0xFF as needed to comply with alignment requirements. No other modifications to frame transmission must occur.

Note

Contrary to the Read Channel, word alignment requirements on the Write Channel do not entail any modification of the Write_Sample_Size field of the Device Descriptor.