[Coco] Re: Re: Questions about the 502 controller vs the Disto SCII

[L. Curtis Boyle]

On Wed, 26 Jul 2006 11:09:13 -0600, Warren Hoslet <dermunda at hotmail.com>  
wrote:

>>> I did have no halt setup when I had my multipak and B&B harddrive   
>>> controller
>>> setup. Mr. Gault helped me with that. :)
>>> How would it help playing Kings Quest? I saw its benefits while
>>> multitasking, but if your just playing a game how would it help?
>>    Keyboard type ahead works even when the game is loading the next   
>> picture/map, etc. With a halting controller, all key presses during  
>> drive  access are lost.
>
> How is ho-halt implemented by the SCII? Does it perform disk I/O from a  
> buffer on the controller card without requiring the 6809 to handle the  
> timing-critical task. If the 6809 has to do the work I would think that  
> it would still have to mask interrupts which would prevent keyboard  
> type-ahead. Since I have no technical knowledge of the SCII, I'm just  
> speculating.
>
> - Warren

     The controller does the sector transfer on it's own to an internal  
buffer; the Coco then reads the entire sector's worth of data in one  
chunk, with interrupts still functioning. Quite a few of us tried to get a  
native mode 6309 driver for the floppy controller to be able to read the  
controller live without having to enable the HALT line, but we couldn't  
quite get it fast enough.