for the 8259 PIC:

  when you get an interrupt on one of the IRQ n lines, does the corresponding
  bit in the Interrupt Request Register get set regardless of the Interrupt
  Mask Register?


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- TODO -
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compile on as many machines as possible.

write document for developers outlining steps necessary to add devices.

add support for file descriptor events.  maybe can test with stdin.

print code out.  have a thorough look.

make a macro to check for events etc. so it can easily be called
  multiple times.

write LICENSE stuff.


*** remember to send manual EOI after interrupt routine ends.
  bx_outp(0x20, 0x20)  for EOI irq 0..7
  bx_outp(0xA0, 0x20)  both needed for irq 8..15

  and to enable IRQ 2 for cascade to slave PIC.
  bx_outp(0x21, bx_inp(0x21) & ~(1<<2));

bx_poke() ??? --> bx_access_physical() ???

complete initialization of BIOS data items for PIT, etc.

does INT 13h function 1 (Read diskette status) reset the status value to 0?

make new dependencies in Makefile for io_*.h files

change disk_param_table values.  modified them to see if
it would help the boot process.

