Re: [RFC PATCH v2 09/14] m68k: hp300: Remove hp300_gettimeoffset()

[Geert Uytterhoeven]

Hi Finn,

On Wed, Nov 21, 2018 at 10:47 AM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 21 Nov 2018, Geert Uytterhoeven wrote:
> > The 8520 CIA is almost identical to the 6526 CIA, as used in the C64...
>
> The 6526 CIA datasheet says, "In continuous mode, the timer will count
> from the latched value to zero, generate and interrupt, reload the latched
> value and repeat the procedure continuously."

I stand corrected...

> This suggests that either 0 or N (the latched value) would result from a
> read from the counter immediately following an interrupt. Who can say
> which? Just have to try it. The answer should allow us to avoid the risk
> of a clocksource that jumps forwards and backwards.

The code in amiga_gettimeoffset() does:

        ticks = hi << 8 | lo;

        if (ticks > jiffy_ticks / 2)
                /* check for pending interrupt */
                if (cia_set_irq(&ciab_base, 0) & CIA_ICR_TA)
                        offset = 10000;

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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