[sdiy] My New Project - PCSYNTH

[Scott Gravenhorst]

Nils Pipenbrinck <np at inverse-entertainment.de> wrote:
>Scott Gravenhorst wrote:
>
>> No, but I do plan to test an Intel Pentium with the same program to 
>> see if this is common.  I'd
>> read that port operations are slow, but that is a bit slower than I 
>> expected.  My assembler book
>> lists "out" as a 13 cycle instruction, but 1.5 uS is FAR more than 13 
>> uS at 133 MHz.   
>>
>Scott, that's just the pure instruction count for the out itself. You 
>have to take into account that you get *lots* of additional waitstates 
>for the ISA-bus. In reality it's somewhere between 300 and 500 cycles 
>average. Depends on a lot of factors, hardware, ISA-bus clockrate, 
>chipset and so on.
>Try it yourself, just try to write the vga palette index port 0x3c8 and 
>the color registers 0x3c9 as fast as possible and measure the bandwidth. 
>You'll be surprised how slow it is.
>
>I'd say that you'll need a DMA based I/O card.

That's one way to do it.  I prefer not to use DMA.  I want _simple_.

I really like Roman's idea of hacking off and using the edge connector of
a defunct ISA card, stick a 16 bit latch on it and go with memory mapped
I/O to the DAC.  A simple, fast mov will load the DAC.  That would make
this thing scream (except for the two "in" instructions required to get a
MIDI byte, but that's only 3 uS instead of 9).

>
>btw, I tried to write you directly, but your email provider blocks my 
>email....

Yeah, email has gotten weird THANKS TO SPAM.  My mom can't get my emails
at all, they used to go into her "bulk" folder, now they just go into a
bit bucket.


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