[sdiy] Re: PCSYNTH Web Page Up

[Scott Gravenhorst]

Magnus Danielson <cfmd at bredband.net> wrote:
>From: Helen Austin <gwenhwyfaer at gmail.com>
>Subject: [sdiy] Re: PCSYNTH Web Page Up
>Date: Wed, 8 Jun 2005 09:47:32 -0700
>Message-ID: <df5b05ea05060809471f719a0b at mail.gmail.com>
>
>> On 6/8/05, Scott Gravenhorst <music.maker at gte.net> wrote:
>> > There is also an explanation as to why I designed an 8 bit memory cycle ISA
>> > card instead of a 16 bit memory cycle ISA card.
>> 
>> Just a quick comment. You plan to decode the addresses so that
>> $B8000 and $B8002 are the low and high byte of the DAC. Why not decode
>> them so that $B8000 is the low byte and $B8001 is the high? That way
>> you can use a single 16-bit MOV to write to the DAC; the ISA bus
>> management should translate them automagically. Then the code
>> becomes shorter, and you can get more of it into the CPU's cache.
>> (It also becomes simpler and more direct to write.)
>> 
>> Helen (following this thread avidly!)
>
>Good point. Since the introduction of the IBM AT and its 8 MHz 80286, the
>IBM A bus (later named ISA) is a 16-bit bus and since then doing 16 bit
>transfers makes sense. The instructions supports it from the 8086, but the
>IBM PC bus was only 8 bits (and hence only an 8088 was used).

I will fix this.

>Remember, the x86 have least significant first so Helens address map is the one
>to use.
>
>I have been following this thread too, and I'd like to point out that DMA is
>fairly simple to do, but with todays speeds it not as much of an issue. But
>more importantly a little buffer for a few words is a good thing. Also, I got
>myself a bunch of full-length lab-boards for about 15 USD each, so I got a pack
>of 5! I gave away one to a friend in need. I wonder whatever happend to that
>project. You guys have me wondered for the first time in years!

The problem with DMA and a sound card is that different sound cards have
different control electronics and therefore may required different DMA
programming.  If I write it for a soundblaster (which are the only cards I
have), then it may not work for those who selected different soundcards.  I
don't want to write different drivers for different cards.  This simple ISA
interface should be fast enough and should work for everyone, unless I'm missing
something here.


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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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