Is there a data fifo in dsp/bios?

Bryan,

With MSGQ, the messages must have a MSGQ_MsgHeader as it first field. Given that, you could either have the messages contain the entire data packet or it can contain a pointer to the data (and probably a size). For example:

struct MyMsg {
    MSGQ_MsgHeader msgHeader; // required and do not modify directly...use MSGQ APIs
    Char data[1000];
}  

The above approach requires you to know the worst case data size. Note: you can have MyMsg1, MyMsg2, etc and use the MsgId field to help the receiving thread determine what type of message it is.

struct MyMsg {
    MSGQ_MsgHeader msgHeader; // required and do not modify directly...use MSGQ APIs
    Ptr data;
    Int dataSize;
}

The above allows more flexible messages, but does not work on a multi-processor system.

For your case of having the sender (producer) put in X bytes and the receiver (consumer) take out Y bytes (where Y <= X), basically works with MSGQ. If you do the second use case (pass the pointer and size), the receiving thread could still consume the received data as chunks. It would not free the message (or return it to the producing thread) until it was completed with the entire data block in the msg though. There might be some edge conditions (i.e. received msg's dataSize is 500, but you want to consume in 128 chunks, so you'll have 116bytes in the last chunk). Not sure if this is a show stopper or not.

Please refer to the MSGQ documentation in the User Guide and the API Reference for more details.

Having said all this, it sounds like what you really want is a simple circular (or ring) buffer implementation. DSP/BIOS does not provide one. You might want to just take the afternoon and write one up instead of using MSGQ.

Todd