Why MAX_PACKET_SIZE is set to 800?

[desowin]

I briefly checked the OpenVizsla packet format and noticed that there is:
HF0_TRUNC = 0x08, // Clipped due to packet length (> 800 bytes)

Then I noticed that this seems to originate from the software/fpga/ov3/ovhw/whacker/producer.py which has the MAX_PACKET_SIZE = 800.

Is there any actual reason why there is such an arbitrary limit set? Why not make it 1 + 1024 + 2 = 1027 (PID + Data payload + CRC-16) to match the USB 2.0 high speed maximum for interrupt and isochronous transfers?

[somehdlguy]

I don't have a good answer as to why we chose 800 as a maximum packet size. I'll have to revisit the code to determine if there is a good reason. I'll try to do so in the next few days.

The packetization code is a bit arcane. Choices in there have implications in the SDRAM access patterns, packet streaming to the host and other areas I probably don't remember. Some other analyzers just double each byte to a value/flags tuple to avoid this complexity, but we felt this was an unacceptable impact to capture bandwidth.