By default the TomTom One doesn’t give console access over ttySAC0, instead it looks like a plug & play daemon periodically polls the port possibly for a GPRS modem. A few attempts at allowing access to the shell with TomTom Navigator running concurrently failed so rather than modifying the ttpnpd file that I use to launch my main application I created a file called SerialTTY.cap in the SDKRegistry directory:
Version|100| AppName|SerialTTY| AppPath|/mnt/sdcard/bin/| AppIconFile|tty.bmp| AppMainTitle|Serial TTY| AppPort|2001| COMMAND|CMD|cmd|tty.bmp|SerialTTY|
And in the bin directory created a small shell script called SerialTTY to perform the redirection between the shell and the /dev/ttySAC0 port:
stty -F /dev/ttySAC0 115200
sh < /dev/ttySAC0 > /dev/ttySAC0 2>&1
All works well and after the initial period I didn’t see any more interference from the plug & play daemon. I noticed in the /bin directory (on the internal filesystem) that the lrz binary is provided and successfully used it to perform a zmodem file transfer. In conjunction with a few scripts this may be a more convenient way to transfer new binary images to the device rather than going through the reboot required when using the USB mass storage interface.