Explicit packing of Command/Status

[quetric]

This PR has two changes:

• added bytesReceived and endOfPacket fields to hlslib::axi::Status which are set by datamovers when Indeterminate BTT mode is set
• added constructors and casting functions enabling easy explicit conversion of Command/Status to/from ap_uint. There appears to be a problem with tight packing of structure fields on stream interfaces in the latest Vitis HLS, therefore this change makes it easier to do manual packing.

[definelicht]

Thanks Lucian -- you didn't change the internal representation of the objects, doesn't that mean that they will still not be tightly packed in the HLS code? I was thinking something like this:

class Status {
   Status(ap_uint<4> tag, ap_uint<1> internalError, ap_uint<1> decodeError, ap_uint<1> slaveError, 
          ap_uint<1> okay, ap_uint<23> bytesReceived, ap_uint<1> endOfPacket) {
    data_(3,0) = tag;
    data_(4,4) = internalError;
    data_(5,5) = decodeError;
    data_(6,6) = slaveError;
    data_(7,7) = okay;
    data_(30,8) = bytesReceived;
    data_(31,31) = endOfPacket;
  }
  ap_uint<4> tag() const {
    return data_(3, 0);
  }
  // Repeat for all fields...
 private:
  ap_uint<32> data_;
}

Wouldn't this guarantee tight packing?

[quetric]

I didn't think of changing the underlying storage tbh. The way i used the code in this PR is to have ap_uint streams on interfaces and convert to and from Status/Command for internal use. Something like:

void err_forward(hls::stream<ap_uint<32> > &status, hls::stream<ap_uint<32> > &error){
    hlslib::axi::Status sts = hlslib::axi::Status(status.read());
    if(!sts.okay) error.write(sts);
} 

The result is tightly packed because ap_uint is what's streamed. But your solution is better because it allows the Status/Command to be carried directly on the stream. I can give it a try in a few days, unless you want to make the change yourself.

[definelicht]

Then I like my solution more, if it works. But the critical thing to check is that the size of the struct containing the ap_uint is equal to the naked ap_uint, also for non-byte aligned structs. No rush from my side!