[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Ok, anyone started Contiki 4 AII yet?

desiv wrote:

I was checking on the web and saw the SSC jumper settings...  Found this
quote:
_______________________________________________________
A little theory:

SW2-6 controls whether interrupts from the SSC are enabled.  They are
enabled in the ON (UP) position.

If SSC interrupts are enabled, and the CPU has enabled interrupts, _and_
the 6551 chip on the SSC is activated (by turning on the DTR output),
then an interrupt will occur for any change of state in the DSR or DCD
inputs, or for transmit data complete or receive data pending (if those
interrupt sources are enabled in the 6551 registers).
______________________________________________________
Since most people will be using serial (SLIP (or eventually PPP)), seems
like a logical choice...
However if t is generating interrupts based upon DTR and DSR then these will not be consistent in timing and could cause problems. 



When and if there's a TFE card for the Apple, putting a timer on it would
make sense, and thus 2 versions.  Ethernet and Serial, each with it's own
interrupt.

Or, you could assume that all people have a SSC.

1 issue, apparently enabling the interrupt on the SSC can cause problems in
some standard apps.  More quote:
_____________________________
If the application doesn't have an interrupt handler installed, then the
occurrence of an interrupt will immediately cause the system to crash.

The reason that you aren't seeing a problem with DOS 3.3 is that DOS 3.3
disables interrupts (in the CPU) when it starts booting, and doesn't
normally enable them again (an application might do so).  By comparison,
ProDOS-8 version 1.2 and later disables interrupts during boot, but
enables them once the PRODOS file has been loaded.  (They are disabled
during all subsequent 5.25" disk I/O operations, and possibly at other
times, but the previous disable/enable state will be restored
afterwards.)
If CPU interrupts are disabled during disk access disk access this could cause serious timing problems. What is needed is a consistent source of timing. 



In theory, with SW2-6 in the ON position, what is supposed to happen is
that your machine will run fine as long as you don't try to do anything
which enables the serial port hardware (such as a PR#2 command).
Enabling the serial port risks a crash due to lack of interrupt
handlers.  The serial port should only be used while running
communications software which has an appropriate interrupt handler.
_______________________________________________

Just some info...

desiv






--
Rob
"Never ascribe to malice that which can be adequately explained by stupidity"