CIA pins bit-banging: how fast?

[tnt23]

All,

I am confused regarding CIA access speed. I need to determine just how fast these can be accessed.

In hackdisk.device, there's a piece of code that gets the ID of floppy drive(s) attached to Amiga. It involves asserting and deasserting certain floppy bus pins (SELx and MTR) as well as reading RDY pin, according to the algorithm covered in Amiga tech docs.

The code looks as follows:

Code: [Select]


move.l  #ciabprb,a0
bset    d1,(a0) ;motor
bset    d3,(a0) ;deselect
bclr    d3,(a0) ;select
bset    d3,(a0) ;deselect drive


I have read that CIAs are clocked at ~700kHz (F/10) no matter what Amiga it is and how fast the CPU runs. Does that mean the CIA won't be able to properly toggle its pins when this code is run by some 68030@25MHz, or that the fast clocked CPU would slow down when talking to slow clocked CIA? Please help me out :-?

[Zac67]

Accessing the CIA adresses will slow down the CPU to the required speed (through the bus interface (glue) logic).

[tnt23]

Zac67 wrote:
Accessing the CIA adresses will slow down the CPU to the required speed (through the bus interface (glue) logic).

Thanks!