35s program checksums

[MarkHaysHarris777]

(03-29-2014 11:35 PM)r. pienne Wrote:  I know Pauli's famous HP 35s bug list says "checksums are meaningless", but I'm wondering has anybody here managed since to figure out any consistency at all in them?

Some of the bugs on the bug-list are really quirks. For instance, number 15. Yes, some programs cannot be interrupted... especially if you put a tight loop in them! It has nothing to do with whether the program should be interrupted without a PSE, its that the PSE breaks the tight loop allowing the firmware to 'see' the interrupt. The 35s is using 1980's technology-- its 8502 processor core primarily. Welcome to 8 bit unprotected 'slow' programming.

The checksum and program size numbers are NOT a bug, nor are they meaningless. The problem is that the slightest change in the 'stored program' including the label or spaces changes the check sum. On my 35s the same program instructions keyed against the same label 'always' produce the same check sum. The sample programs from the manual always produce the same checksum in my unit, and the program lengths in bytes are always consistently the same... also reflected in the decrement of available bytes from the heap. If you key a program into label P the checksum will be different than the 'same' program keyed into label A, or Q. A program without a label will produce a different checksum than the very same program keyed with a label.

I am still working on verification of this next point. I suspect that the 'order' of the program labels alphabetically in relation to the top and bottom of program space may affect the checksum (I'll get back to you on that).

The bottom line for me is that I cannot reproduce the checksum|size bug on my 35s unit/ its very consistent.

Cheers