8

For an OCS Amiga (Workbench 1.2 or 1.3) I remember sometimes after a Guru Meditation/software failure reboot, Workbench would be restricted to NTSC size displays (200 non-interlaced vertical lines in stead of 256) until the next reboot.

This was an occasional thing, the only pattern I could see was that it was typically after some crash. Has anybody got an idea why that might be?

  • Might it be due to the video being in NTSC mode when the crashed occurred? – Tim Locke Aug 15 '16 at 22:35
  • Might be (can't remember though), for me the question then becomes why it would retain that mode for only one reboot.. – nsandersen Aug 16 '16 at 5:51
  • Is this on a real machine? Which Agnus chip is installed? – user180940 Aug 17 '16 at 11:15
  • It was on a real machine. I remember it most on an Amiga 500 with Kickstart 1.2 AND 512MB RAM. I have a feeling I saw it on my A1200/KS3.0 once too, but don't quote me on that. – nsandersen Aug 17 '16 at 11:50
  • Do you know which Agnus did that A500 have? Or the motherboard revision? BTW, I remember that bug too on my 1.2 A500. I never saw it later on my 2.0 ECS A500+. – user180940 Aug 17 '16 at 12:46
6

At startup, the Amiga used a timing routine to check the frequency of the AC power supply, and start in PAL (50 Hz AC) or NTSC (60 Hz AC) appropriately. Unfortunately, the detection was buggy, and sometimes 50 Hz was wrongly identified as 60.

Many Europeans would have Declan McArdle's NoPALReset in their s:startup-sequence to avoid this. I think the problem went away with Fat Agnus-level hardware and later.

  • That's interesting. How would it measure the frequency? – nsandersen Aug 19 '16 at 8:56
  • 1
    It was not the mains power frequency that is measured: instead, the vertical beam position is read to see if it ever reaches lines above 260, something that can only happen in PAL. In the Kickstart 3.1 code, this is done at startup by graphics.library (as a fallback for earlier Agnuses that were not multistandard). As scruss said, most likely the routine was not working as expected sometimes, so the OS comes up believing it's NTSC rather than PAL. – user180940 Aug 19 '16 at 9:12
  • I don't have a source for my mains frequency comment, so your beam position reading is more likely. – scruss Aug 19 '16 at 13:40
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    @user180940 That sounds like an answer, not a comment. – a CVn Aug 19 '16 at 15:24
  • some games even have "region lock" (mainly Psygnosis) to detect if the game runs on NTSC or PAL. It's measuring the time the beam runs to the bottom of the screen smth like that. so it can be done by software, yes – Jean-François Fabre Dec 29 '17 at 19:41

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