🚀 go-pugleaf

>>>>> On 2 Nov 92 14:14:03 MDT, sl8nl@cc.usu.edu said:
> code.  Bear in mind taht this is from some communication routines that I have.
> This is one section of the code (from what I can remember off the top of my
> head).  I'd ask the original programmer, but there is no address.
(I have rewritten the code in more compact form to save net bandwidth):
	outp(0x20,0x11);	/* ICW1: cascade, edge triggered, normal */
	outp(0x21,0x08);	/* ICW2: base int=8, normally */
	outp(0x21,0x04);	/* ICW3: slave at IRQ2, normal on AT */
	outp(0x21,0x03);	/* ICW4: auto EOI - no need for out 20,20
				 *	 non-buffered mode
				 *	 no special fully-nested mode */
	outp(0x20,0x20);	/* OCW: End-Of-Interrupt */
> What exactly does this do?  The interrupt won't run without it (although it
> should).  The actual interrupt also doesn't use a mov al,20h; out 20h,al at the
> end of the interrupt.

It is almost same as AT or 386 computer BIOS does on initialization
of 8259 (I looked BIOS code on two computers here), with one exception:
the auto-EOI which is not set by BIOS (XT 8259 programming is *MUCH*
different since XT has only one 8259, MUST NOT program cascade mode).
The auto-EOI means no need for out 20h,20h on every interrupt.