From: Carl Eike Hofmeister <ceh@ca...> - 2007-01-27 13:37:01
I would like to connect a modem to a gumstix (to build a low
power fidonet system).
To make this work reliably, this requires RTS/CTS (the gumstix
doesn't know how slow the modem is currently working) and
DCD/DTR (to check connect and to hang-up).
by building an expansion board for the FFUART. The 60 pin
connector exposes all required pins. On software-side this
just seems to require selection of the correct mode for
To still use USB:
should the expansion also include an USB port, CTS/RTS lines
of the FF can not be used. It just seems to be configuration
to use other pins in gumstix.h, possibly gpio81/83 like on the
So far, this doesn't seem to be too difficult. But instead of
the USB port I'd like to have a network port.
The netstix 92-pin expansion however, uses the GPIO36 as
interrupt line, which happens to be the FF's DCD line.
The netduo uses gpio27 for the 2nd network port, a good
indication that gpio27 might also be suitable for the first
port. So to make option 1 work with a netstix i would lift
gpio36 on the 92pin connector off the board and connect it to
gpio27, which is located right next to it. Also, SW config
needs to be swapped.
the PXA manual states that the additional modem lines can be
emulated by any of the GPIOs. So an expansion board could be
build e.g. using the HWuart on 42-45 (I assume 48-51 used
for the netstix are not operated in HWUART mode), and use any
free GPIOs for DCD/DTR. The difficulty here seems to be the
software implementation: I think the PXA driver expects a
complete modem status register, and this would then need to
be filled with data from different pins. If this can be
configured I couldn't find it.
Currently the easier alternative seems to be option 1.
Did anyone try this or something similar?
Anything else needs to be done I missed?
Thanks for any kind of advice.