linux-kernel - Re: [RFC PATCH v2 09/14] m68k: hp300: Remove hp300

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Message-ID: <alpine.LNX.2.21.1811212032550.275@nippy.intranet>
Date:   Wed, 21 Nov 2018 20:47:44 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     Kars de Jong <jongk@...ux-m68k.org>,
        Philip Blundell <philb@....org>,
        Andreas Schwab <schwab@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        Stephen N Chivers <schivers@....com.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Michael Schmitz <schmitzmic@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 09/14] m68k: hp300: Remove hp300_gettimeoffset()

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."

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.

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