[Coco] NitrOS-9 newbie needs some help

[Robert Gault]

KnudsenMJ at aol.com wrote:
> In a message dated 8/9/04 8:57:13 AM Eastern Daylight Time, 
> boisy at boisypitre.com writes:
> 
> 
>>NitrOS-9 definitely pushes the CoCo harder than RS-DOS, there is no 
>> question about it.  While all of the CoCo 3s I have here will boot 
>> NitrOS-9, I've heard reports that some CoCo 3s will just flat out not 
>> boot at all.  The reasons are probably numerous, but I think it all 
>> boils down to timing and stability of hardware.
> 
> 
> A similar argument is often made about PCs that run Windows just fine, but 
> won't install Linux without crashing.
> 
> Question for Boisy: Is there any reason why Nitros should be any harder on a 
> Coco3 than Tandy OS-9?  Does it bang on the GIME any more than Tandy?
> 
> The answer may be different for 6809 and 6309 versions of Nitros.
> --Mike K.
> 
The GIME probably gets the same amount of usage for both OS-9 and 
NitrOS-9. There is very significantly difference regards the disk 
controller.

All the current NitrOS-9 disk I/O has been converted to "no blob" timing 
for both boot and normal use. This helps enormously during the boot 
process and is not expected to have any ill effects during normal usage.

Here is the critical difference in the two routines during a read sector:

    Stock Disk Basic & OS-9                "No Blob"
loop  lda  $FF4B    get data         loop  lda    $FF4B
       sta  ,x       put data in buffer     sta    ,x+
       stb  $FF40    tickle the FDC         nop
       bra  loop                            bra    loop

The loop is exited with an NMI from the FDC. On most systems, the above 
change prevents "boot module order crashes" in OS-9 and has no effect 
with normal disk I/O. Perhaps some hardware won't like the above and 
protest.