Re: MacPPC serial ports in 4.0.1 - not quite

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

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Hello,

On Dec 30, 2008, at 1:38 AM, der Mouse wrote:

> It's reminiscent of my own experiences with macppc serial; I found  
> that
> if I used the serial line for anything substantial it would wedge in
> some way.  That machine seems to have stopped working, though, and for
> the next week I'm in the wrong city to investigate.  My macppc issues
> were with 1.4T, which seems to point towards it being something very
> long-standing.

Pre-4.0 macppc had completely hosed interrupt handling. It would lose  
interrupts left and right, level-triggered interrupts didn't really  
work at all, edge-triggered ones ( like serial ports ) were likely to  
get stuck under heavy load.

Donald's G3 uses a Heathrow PIC, basically two old style PICs glued  
together to allow 64 IRQ lines. For the serial ports it shouldn't make  
any difference, only the onboard ethernet controller and some other  
device I forgot about uses IRQs >31, the serial ports are where they  
used to be on Grand Central and the likes.
What I'd suggest is to have a look at arch/macppc/macppc/ 
pic_heathrow.c and add some debug code that checks wether edge- 
triggered interrupts get properly dealt with. These old PICs are prone  
to lose interrupts, if you disable one, it fires and then you re- 
enable it you won't get an interrupt. So what we do is to check the  
appropriate registers when enabling an interrupt and mark it pending  
if we find it already active. This seems to work fine for almost  
everyone but in this case that's still the first place I'd look at.

have fun
Michael

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