Subject: Re: comprobe and a GoldeGateII attached ISA bus

From: [email-masked] (Niklas Hallqvist)

>>>>> "Charles" == mycroft  <[email-masked]> writes:

Charles> Actually, the com probe sequence is a bit braindead.  It
Charles> would be better to tickle the chip and see if it interrupts.
Charles> I'm not sure if there's a general way to do that without
Charles> outputting a byte, though.  (Loopback mode doesn't work on
Charles> some clones.)

After speaking to several people I've got the conclusion that the ISA
bus *cannot* guarantee a 0xff value when reading an unexistant port.
Apparently, some busses keep a voltage in the middle of a logical zero
and one (for a fast switch time), some busses are pulled up, some are
pulled down.  Do you have the 16450/550 specs?  If we not do the tickle
probe, we might maybe go for a better kind of passive probe.  Anyway,
is it so bad to output something during probe time?  A break signal
maybe?  I understand this is low priority, but maybe sometime...

Niklas

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From: "Charles M. Hannum" <[email-masked]>

Anyway, is it so bad to output something during probe time?  A
   break signal maybe?

A break signal would not cause an interrupt.

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From: [email-masked] (Niklas Hallqvist)

Niklas

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From: "Charles M. Hannum" <[email-masked]>

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From: [email-masked] (T. William Wells)

In article <[email-masked]>,
Charles M. Hannum <[email-masked]> wrote:
:    Anyway, is it so bad to output something during probe time?  A
:    break signal maybe?
:
: A break signal would not cause an interrupt.

However, a break would prevent anything transmitted from further affecting
the transmitter output, as a break signal overrides the normal serial output.

Be that as it may, it is possible to generate the interrupt without
transmitting anything; I do it in my driver. The question I have is: what is
the proper way to detect the interrupt in a probe routine?

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From: "Charles M. Hannum" <[email-masked]>

Be that as it may, it is possible to generate the interrupt without
   transmitting anything; I do it in my driver.

Would you care to state *how*, rather than simply asserting that you
do it?

As has been pointed out, neither using the loopback mode nor expecting
an interrupt if you enable the chip with an empty transmit buffer are
reliable methods of getting an interrupt on clone devices.