RTC runs too fast in NTSC

[rhester72]

When the system (not screen mode!) is set to NTSC, the real-time clock advances much too quickly (owing to the difference between 50Hz and 60Hz tick). When the system is set to PAL, the clock runs normally.

[sorgelig]

Noted. will check it.

[rhester72]

Apologies, I think I worded this poorly.

RTC itself (the real RTC) is just fine. It appears to be CIAA (or CIAB or both? I don't remember which Kickstart 1.x uses vs. 2.x+) TOD that's the problem.

How to reproduce:

• Boot Kickstart/Workbench 2 or 3 in NTSC mode (again, not screen mode, in NTSC in Minimig)
• Open a CLI, note the time
• Let it sit for several hours
• Note the time again, it will be several minutes slow (so we know the TOD is behind, running at 50Hz)
• Run "setclock load" to refresh the TOD from the RTC
• Note the time jumps ahead to the correct time (proving the RTC proper is actually good)

Hope this helps clarify :)

[sorgelig]

Are you talking about NTSC mode you can choose if you boot Amiga with both mouse keys held down, and choose in that boot menu? So you use PAL mode but temporary choose NTSC in boot settings?

[rhester72]

No, the other way - selecting PAL in the core itself under video settings.

Working now to put together the smallest possible package with config, rom and adf to reproduce.

[rhester72]

minimig_clock_test.zip

Attached are a minimig config (only change from defaults is "Audio & Video/TV Standard" is set to NTSC, which is key to triggering the problem), a Kickstart ROM of standard 3.1 for 68000, and a Workbench 3.1 ADF with NTSC and PAL monitor drivers (for convenience, screenmode does not affect the problem) and Clock set to start automatically.

Steps to reproduce:

• Unzip the contents to SD card
• Start the minimig core
• Insert wb31test.adf info DF0:
• After booting, a digital clock should appear

Let it remain in that state for a while (hours, ideally) and you will observe it consistently losing time compared to wall clock. RTC is unaffected - if you wish, open a shell and execute "setclock load" and you will observe the time "snap" back to current.

This problem ONLY occurs if the core is set to NTSC video. If you repeat the above steps but first set the core to PAL, the problem will not occur.

Please let me know if there's anything else I can do to help.

[sorgelig]

Since Minimig includes RTC, do you think WB still gets time from CIA instead of RTC?

[sorgelig]

RTC in minimig core gets update every minute, so time must be not from RTC.

Looking as A1200 schematics, CIA gets clock from VSync which is obviously 20% faster in NTSC mode. It seems AmigaOS/WB should detect NTSC mode and program CIA accordingly. So it must be something inside Amiga software. I don't know why NTSC time running faster. Did you try additionally boot into Amiga boot config and choose NTSC mode there additionally?

[rhester72]

It's definitely not a software bug, I've been running NTSC workbenches for almost 40 years. =)

CIA can get its clock either from vsync or from power, automatically detecting 50/60Hz from that. Is the latter updated? (I'd need to consult WinUAE to see which one the A1200 uses specifically, it varies by model.)

[sorgelig]

CIA-A gets tick from VSync, CIA-B from HSync. Same as in A1200 schematics.

[sorgelig]

Considering that A1200 can output wide range of frame rates i don't know how software can relay on such timer. A500 is less flexible in video output but still..

[rhester72]

I confirmed only the A1000 and A3000 sync CIA TOD off of the power source, all others is indeed vertical sync.

I do not know the specifics of how it's done in Kickstart (or SetClock), but I know for sure there would have been a bug report or three if every American Amiga user couldn't depend on the time. laughs BBSes were quite big over here for a while...