MMFS Bad sum?

discuss both original and modern hardware for the bbc micro/electron
Post Reply
User avatar
0xC0DE
Posts: 630
Joined: Tue Mar 19, 2019 7:52 pm
Location: The Netherlands
Contact:

MMFS Bad sum?

Post by 0xC0DE » Sun Nov 24, 2019 11:35 pm

Sometimes I get the Bad sum error on MMFS 1.41. Not every time and not always at the same place. What are the main causes of this? Using Ramtop hardware on Electron btw
0xC0DE
"I program my home computer / Beam myself into the future"
:arrow: Follow me on Twitter
:arrow: Visit my YouTube channel featuring my demos for Acorn Electron and BBC Micro

User avatar
hoglet
Posts: 9291
Joined: Sat Oct 13, 2012 7:21 pm
Location: Bristol
Contact:

Re: MMFS Bad sum?

Post by hoglet » Mon Nov 25, 2019 7:42 am

0xC0DE wrote:
Sun Nov 24, 2019 11:35 pm
Sometimes I get the Bad sum error on MMFS 1.41. Not every time and not always at the same place. What are the main causes of this? Using Ramtop hardware on Electron btw
A small part of the MMFS workspace (15 bytes) is protected by a CRC, because it contains critical information, such as the start sector of the BEEB.MMB file. If this were corrupted, other files on the SSD might be damaged.

A Bad Sum error occurs when the CRC check on this region fails, because something other than MMFS has written to this region.

(In ESWMMFS, I think this region is at &B7E0 to &B7EE)

One possible cause is a game whose rendering code is buggy, and sometimes writes to the the ROM area above the screen memory.

Dave

User avatar
0xC0DE
Posts: 630
Joined: Tue Mar 19, 2019 7:52 pm
Location: The Netherlands
Contact:

Re: MMFS Bad sum?

Post by 0xC0DE » Tue Nov 26, 2019 9:00 am

Thanks Dave. It's my own code that this is happening with. But not very often and I can't reproduce the Bad sum error even on consecutive runs of my program. Will have to investigate further. I thought maybe there could be other causes triggering this error.
0xC0DE
"I program my home computer / Beam myself into the future"
:arrow: Follow me on Twitter
:arrow: Visit my YouTube channel featuring my demos for Acorn Electron and BBC Micro

Post Reply

Return to “8-bit acorn hardware”