Re: OldWorld floppy and serial port work

[Michael <macallan%netbsd.org@localhost>]

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Hello,

On Jul 8, 2010, at 12:46 PM, David Riley wrote:

> Well, that's the problem; I have a 9600, which is probably somewhat  
> different than the serial port on the G4 (which is built in, but not  
> exposed by default, and I wonder if it's different hardware).  All  
> the way back to the original Mac, they've used a Z8530 (just like  
> Sun and everyone else who wanted a *real* serial chip), and mac68k  
> works fine.  For me, if I look at a man page, it stops responding to  
> serial commands (though it'll still output log messages, which is  
> puzzling).  The system log doesn't output any debug info, so I'll  
> probably have to start from the top.

I would suspect interrupt problems. The G4 has a completely different  
interrupt controller ( OpenPIC instead of Apple's own ) which should  
not lose interrupts but Apple's might. If we enable an interrupt line  
that's already asserted it will not cause an interrupt for example.  
There is code in place to check this condition, it works fine with  
other devices but occasionally weird things happen - for example I get  
lost interrupt messages from the IDE chip on my beige G3 on first  
access to the disk with no further ill effects. And this does not  
happen with any other Apple IDE chip so it's probably a Heathrow thing.
So, first thing I'd do is to run systat 1 vmstat and check if the  
serial port's interrupts still fire when thinks lock up and you keep  
sending. Since it happens on a G4 as well it's very likely not the  
actual interrupt dispatching code but something in the macppc-specific  
portion of the zs driver. In other words, what Donald Lee said.

have fun
Michael

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