Subject: Re: com.c patch to track PPS
To: Jonathan Stone <jonathan@DSG.Stanford.EDU>
From: Bill Studenmund <>
List: tech-kern
Date: 02/07/2000 10:33:12
On Sun, 6 Feb 2000, Jonathan Stone wrote:

> In message <>
> Bill  Studenmund writes:
> >line (snippet taken from the zs driver). It's in the delta code, and drops
> >transmission if any of the bits in cs_rr0_mask are cleared.
> >
> >Given the case of transmitting when DCD is asserted, that's wrong.

That should have read something like given the case of transmitting when
also doing PPS..

> Isn't DCD active low?  There was some confusion over what "assert"
> means, the PPS-api says "assert" is when you have carrier.

"low" and "high" are confusing in RS-232. Since a "1" is a voltage lower
than -3 V, and a "0" is one over +3, "active low" is rather ambiguous.

I think what the chips do is that a "1" in the status register means
logically asserted.

> But yep, thats one reason I left the sc_msr_mask alone.  The other is
> that I think the com driver takes interrupts for DCD changes even if
> MSR_DCD is off in sc_msr_mask.

Then that's a difference between the drivers. The zs driver only asserts
interrupts for the bits set in cs_rr0_mask.

Take care,