[sdiy] My New Project - PCSYNTH

[Nils Pipenbrinck]

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.

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

Nils