DOS ain't dead - Waiting for 3 (or 3.3) microseconds? 286 and up.

Waiting for 3 (or 3.3) microseconds? 286 and up. (Developers)

posted by myrkraverk, 09.12.2012, 23:41

Hi all,

Context. I've been playing with Sound Blaster coding, so far in DOSBox. The initialization routine is supposed to wait for 3 or 3.3 microseconds between the first two writes for the actual hardware. The docs I've found don't seem to agree on which. And at this point, it probably doesn't matter.

What is a good way to guarantee a wait for a few microseconds? Can I use the same code on a 286 while still guaranteeing long enough delay on a 64bit cpu who happens to be talking to a real sound blaster in an ISA slot? Those motherboards exists [even though I don't have one, nor a real sound blaster].

So far, I've just used interrupt 0x15 with ah=0x86 for a 1000 microsecond delay; which is long enough though quite excessive.

I believe I'm looking at the official documents, where they use a delay loop of "dec al; jnz delay" where al has been initialized to 0. Hence looping 255 times. I'm not sure that method is "future proof" or even sufficient with a modern CPU.

Also related. The Sound Blaster is said to take 100 microseconds to initialize itself. What steps can I take to wait just that long until there is 0xaa from the status port of the card? Again, those steps should ideally work on both real 286 and a modern CPU.

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Complete thread:

Waiting for 3 (or 3.3) microseconds? 286 and up. - myrkraverk, 09.12.2012, 23:41
- Waiting for 3 (or 3.3) microseconds? 286 and up. - RayeR, 10.12.2012, 03:09
- Waiting for 3 (or 3.3) microseconds? 286 and up. - Japheth, 10.12.2012, 11:42
  - Waiting for 3 (or 3.3) microseconds? 286 and up. - RayeR, 10.12.2012, 18:04
- Waiting for 3 (or 3.3) microseconds? 286 and up. - bretjohn, 10.12.2012, 15:52
  - Waiting for 3 (or 3.3) microseconds? 286 and up. - myrkraverk, 10.12.2012, 21:22
- Waiting for 3 (or 3.3) microseconds? 286 and up. - myrkraverk, 10.12.2012, 21:16
- Waiting for 3 (or 3.3) microseconds? 286 and up. - Rugxulo, 10.12.2012, 22:03
  - Waiting for 3 (or 3.3) microseconds? 286 and up. - myrkraverk, 13.12.2012, 14:07
    - Waiting for 3 (or 3.3) microseconds? 286 and up. - marcov, 13.12.2012, 22:51
      - Waiting for 3 (or 3.3) microseconds? 286 and up. - RayeR, 14.12.2012, 01:12