HP-IL checksums or not

[hth]

(11-27-2017 05:58 PM)Christoph Giesselink Wrote:  Last rhetorical question, how do you verify data transfers on HP-IL when the controller is listener and one device is talker? The controller is initiating the transfer with a SDA and the talker device respond with the first data byte. In the next step the controller send the received data byte as request for the next data byte until the controller receive an EOT data frame. So the received data is definitely different from the send one, so the controller has no change to verity the received data for correctness. So any verification of data correctness must be done by the data management itself.

Christoph

Thank you for the interesting information!

HP-IL read transfers are verified by the talker (storage device), it sends a DAB (Data Byte) which is passed around the loop, the controller takes the data and passes it on. When it gets back to the talker it checks that it gets back what it sent out, if it is correct it sends the next frame until the ending ETO (end of transmission OK) frame. If a transmission error is detected (it did not get the same DAB back), it will terminate with an ETE frame (end of transmission - error).

Thus, I believe the protocol is reasonable robust as each data frame is checked during transmission.

For the purpose of sending ROMs, I think there should be an application layer that inspects that we got what we wanted. Ideally, it should verify the CRC32 to see that we loaded the intended ROM. I suspect logical errors at this level may be more likely to occur, and as a side-effect it would also verify the data sent.

But feel free to have opinions, I am not stubborn in case people think there ought to be a checksum. It could perhaps even be adaptive in that it could work either with and without a CRC32 checksum in the data file? In that case it could write a CRC32, but allow for reading files either with or without a CRC32.

Håkan