I have a flashing cursor in the top left of the screen on three Beebs (all issue 7), connecting up the Tube Snooper I can see the processor trapped in an endless loop, only interrupts give it a chance to do something else, then back at it, spinning over and over.
It took me a while to find the bit o'code from the disassembly of OS1.2 here https://tobylobster.github.io/mos/mos/S-s11.html unfortunately, despite all the lovely work, I would have preferred the hex address and hex of the instructions to be like a traditional disassembly (maybe I'll fork it into that when I get some spare time)
I assume somewhere BASIC or something is supposed to take ownership and clear the carry flag?
Has anyone seen this before?
Weird problem on a couple of Beebs
- maniacminer
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Weird problem on a couple of Beebs
Big Model B Econet,Master 512,Electron,A3000,A540,Atom,Unilab 3-Chip Plus,6502,Z80,65C816,80186,32016,Matchbox,ARM7TDMI,Master 10/100,PiCoPro,Teletext,Music500,PiSCSI,Challenger3,Gotek,VideoNuLA,GoSDC,GoMMC,Integra-B,RGB2HDMIv4,Epson LQ-850 (for the win!)
Re: Weird problem on a couple of Beebs
looking at that code, the value its using is
.startupMessageSuppressionAndBootOptions = $0267
bit 7 = 0 means ignore OS startup message
bit 0 = 1 means if !BOOT errors from DISC because no language found, then lock up machine
bit 0 = 0 means if !BOOT errors from *ROM because no language found, then lock up machine
(Read/Write using OSBYTE 215)
and bit 0 will end up in the carryflag due to the ROR instruction
and OSBYTE 215 leads here .. https://beebwiki.mdfs.net/OSBYTE_%26D7
plenty of reading here
.startupMessageSuppressionAndBootOptions = $0267
bit 7 = 0 means ignore OS startup message
bit 0 = 1 means if !BOOT errors from DISC because no language found, then lock up machine
bit 0 = 0 means if !BOOT errors from *ROM because no language found, then lock up machine
(Read/Write using OSBYTE 215)
and bit 0 will end up in the carryflag due to the ROR instruction
and OSBYTE 215 leads here .. https://beebwiki.mdfs.net/OSBYTE_%26D7
plenty of reading here
BBC Bs, Master 128s, Master Compact, and Electrons, and an A3000 with an ARM3
Don’t Panic and Always Carry a Towel
Don’t Panic and Always Carry a Towel
- maniacminer
- Posts: 1330
- Joined: Thu Sep 21, 2017 2:59 am
- Location: Cambridge / Singapore
- Contact:
Re: Weird problem on a couple of Beebs
Thanks for the info. It turns out that IC20 had gone "bad" in all the boards. Removing it and testing it, they passed OK, then replacing it with a 74F139 and I could then see that there was not enough time for the circuit to lock on causing weird problems if I could get the machine to boot that it would show several copies of the DNFS ROMs and then randomly lockup. In the end replacing IC30 with a fresh flip-flop cured the problem and the old 74LS139 worked again. Damn these squirrelly Beebs. Now back onto building the 40th Anniversary boards again. Yay!
Big Model B Econet,Master 512,Electron,A3000,A540,Atom,Unilab 3-Chip Plus,6502,Z80,65C816,80186,32016,Matchbox,ARM7TDMI,Master 10/100,PiCoPro,Teletext,Music500,PiSCSI,Challenger3,Gotek,VideoNuLA,GoSDC,GoMMC,Integra-B,RGB2HDMIv4,Epson LQ-850 (for the win!)