HP-IL checksums or not

[hth]

We are talking about different checksums here.

The ROM checksum at the last address is not going to be checked by my routines. I am aware that there are ROMs with incorrect checksum and those would be rejected, which is undesirable. They probably should have a correct checksum, but that is another issue.

Also, when saving an arbitrary 41CL 16-bit 4K page for backup purposes, it may be data and not a ROM image, meaning not all images may even have a checksum last.

The checksum I am discussing here is a checksum outside the ROM, that may be stored at the end of the file (after all data image).

Now, I had the impression that HP-IL is transmission safe (within reason) thanks to the intended checking of every frame sent. This is strongly encouraged by HP, but not mandatory. Apparently this has not been the norm for ILPer and friends which means that the idea I based this on cannot be taken for granted.

As we already use CRC-32 as signature for 41CL ROM images, it would make sense to also use that as the checksum here. Why have two ways of calculating some signature/checksum when we can settle for one?

I intend to make the CRC-32 optional, as there may be an application layer that deals with CRC-32 for signature purposes. Besides, the code without checksums is already out, and I cannot just make it incompatible over night.

My plan is to update the CLILUP ROM at some point and have WRROM16 write the CRC-32 checksum after the ROM image. The RDROM16 read function will check the file size and work both with and without a CRC-32 checksums (obviously no checking in the latter case).

Håkan