[PATCH v4 2/4] serial: mxs-auart: use mctrl_gpio helpers for handling modem signals
marex at denx.de
Fri Nov 7 00:03:11 PST 2014
On Friday, November 07, 2014 at 02:34:31 AM, Huang Shijie wrote:
> why change them to gpio? If we change them to gpio. Could the DMA still
> works fine?
> did you test the DMA with this patch?
> Add Marek for this patch too.
I didn't look too deep into the patch, so here's just my experience:
1) The AUART block signals and GPIO block signals are not sychronised using the
same clock. Therefore, the latency between toggling of the AUART lines and
the GPIO-driven pins will not be deterministic and will vary. There might be
a way to approximate that, but that's definitelly not a reliable solution.
This is very bad for example if you drive RS485 DIR line with the RTS pin as
a GPIO ; the RTS pin will toggle at non-deterministic time compared to the
end of UART transmission. This will trigger bit-loss on the RS485 line and
you just don't want that.
2) Speaking of RS485, there's  and . which I believe apply to any combo
of UART+GPIO toggling.
So I hate to bring the bad news , but UART+GPIO combo toggling is really a bad
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