Hello,
looking at the ARM Integrator patch (which seems to be something
like the reference port for ARM), I'm not really clear about some
of the code:
a) What's the difference between __ipipe_mach_ticks_per_jiffy
and LATCH?
b) Is there some (hidden, intended future) semantics of tscok?
Right now it just avoids that garbage is returned before
the timer is initialized.
c) In the interrupt routine, the comment currently says:
"If Linux is the only domain, ack the timer and reprogram it",
but the actual code looks as if the comment should read:
"If Linux is running natively, ack the timer.
If Linux's the only domain, reprogram it."
What's wrong, the code or the comment?
d) __ipipe_mach_set_dec() sets the next match value of the timer.
But the current counter isn't changed. Correct?
Or is setting the match value and setting the current counter
the same operation on the Integrator?
__ipipe_mach_get_dec() doesn't return the next match value, but
the current actual counter, i.e. some value between 0 and the
next match value. Correct?
And if so, which value? The number of ticks elapsed since the
last match or the number of ticks until the next match occurs?
The names "..._dec" suggest that the integrator provides a clock
register that decrements. The PXA provides clock registers
that are incremented, and the timer used for the Linux ticks
is (in Linux) never reset, but instead the match value at
which an interrupt occurs is incremented on each interrupt.
So, a port to the PXA wouldn't be straightforward, and so I
want to make sure that I really understand the semantics
of the ARM port.
Thanks for any clarifications,
Detlef
--
Detlef Vollmann vollmann engineering gmbh
Linux and C++ for Embedded Systems http://www.vollmann.ch/
Linux for PXA270 Colibri module: http://www.vollmann.ch/en/colibri/
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