Date   : Thu, 05 Mar 2009 00:06:39 +0100
From   : kortink@... (John Kortink)
Subject: Fwd: New Screen Modes with ARM7 Co-Processor?

On Thu, 5 Mar 2009 09:48:45 +1100, "Richard Wilson"
<richard@...> wrote:

> 
>
>> -----Original Message-----
>> From: John Kortink
>> Sent: Wednesday, 4 March 2009 10:54 PM
>> To: bbc-micro@...
>> Subject: Re: [BBC-Micro] Fwd: New Screen Modes with ARM7 Co-Processor?
>> 
>> >I would think that determining which field Odd or Even would 
>> be relatively
>> >easy since the VSYNC is delayed by (R0 + 1) / 2 on the odd 
>> frames only. It's
>> >a relatively simple task to measure the distance between 
>> VSYNC pulses in a
>> >frame by reading CA1 on the System VIA.
>> 
>> That's not how it works.
>> 
>> The length of the vsync and display periods are always
>> exactly the same.
>
>Perhaps you should actually write some code to test this
>instead of just assuming [...]

I have, and the result is exactly 20000 1 MHz ticks
between vsyncs, minus 2 occasionally.

So, apparently, I'm not the one making assumptions.


John Kortink

-- 

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