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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 21 Nov 2018 09:10:44 +0100
Message-ID: <CAMuHMdVQPSE7+Pe64OybnugCx-pLVfKmNS6_4DEofF3XZPBLsA@mail.gmail.com>
Subject: Re: [RFC PATCH v2 09/14] m68k: hp300: Remove hp300_gettimeoffset()
To:     Finn Thain <fthain@telegraphics.com.au>
Cc:     Kars de Jong <jongk@linux-m68k.org>,
        Philip Blundell <philb@gnu.org>,
        Andreas Schwab <schwab@linux-m68k.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Stephen N Chivers <schivers@csc.com.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Michael Schmitz <schmitzmic@gmail.com>,
        John Stultz <john.stultz@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Finn,

On Wed, Nov 21, 2018 at 12:13 AM Finn Thain <fthain@telegraphics.com.au> wrote:
> On atari, the 68901 counts down to 0x01 and raises an interrupt. On mac,
> the 6522 counts down to 0xFFFF then raises an interrupt. No idea about
> amiga (Geert?) -- this has to be handled correctly to get a monotonic
> clocksource. I'll fix this in v3 (where the information is available).

The docs state that the CIA generates on interrupt on underflow, so I
guess that's the same behavior as the 6522 VIA.

Unfortunately the 24-bit ("TOD") counters in the two CIAs run from HSYNC
resp. VSYNC, which depends on the video mode, and thus can't be used
as a monotonic clock source.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds