[Tinyos-devel] tmote P3.6 / P3.7 direction

[David Moss]

This has been sitting on my plate for awhile, and I haven't had time to do
anything about it.  Thank Geoff Werner-Allen for finding and bringing this
up long ago.

 

 

 

Summary of the problem: "Essentially on the TMote Sky (and probably TelosA),
when the serial port is enabled (i.e. the node is plugged in via USB) but
serial support is not enabled in the binary this creates a port conflict
between the MSP430 UART1RX port, which is by default configured as an output
low, and the buffer between it and the FTDI chip, which is trying to drive
the line high. Not only does this sink ~30mA of extra current into the
MSP430 (which is how we found it, trying to do current measurements with the
node plugged in via USB), we're also suspicious that it may cause a port
latch-up which causes the TMote to fail subsequent reprogramming cycles
(until power cycled)." 

 

Proposed solution: "A better/robust approach might be to have MotePlatformC
check the state of P1.2. If it's low, the mote is running off batteries and
the default configuration is fine. If it's high, the mote is running off USB
so P3.6 should be made output-high and P3.7 should be made into an input.

 

I think you could effectively argue that this approach would:

   - Have a *very* small impact on code size

   - Not create any incompatibilities for motes running off batteries

   - Make life a lot better for motes running off USB, regardless of the use
of the serial stack or its configuration"

 

 

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