FTDI USB to serial converter on eBay for $1.82 shipped. Order one for later if not for now.
http://www.ebay.com/itm/FTDI-Adapter-FT232RL-USB-zu-TTL-Serial-fur-3-3V-und-5V-fur-Arduino-PRO-Mini-/172456631436The cheap one (USD $0.78) at this link would probably work too. I just ordered one to play with.
http://www.ebay.com/itm/FTDI-FT232RL-USB-to-TTL-Serial-Converter-Adapter-Module-5V-3-3V-For-Arduino-New-/272501584059Instructions to flash the GPS under Linux
I tested this myself just now (with my own built uploader and firmware)
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set FTDI jumper to 5v or use the 5v pin when wiring a connector on the USB to serial adapter
(the GPS needs 5v to run)
unplug the GPS from the FTDI (USB to serial converter)
plug the FTDI into the PC USB port
type this to make sure your device is called ttyUSB0
ls -lrt /dev
I find ttyUSB0 third from the bottom for my FTDI brand USB to serial converter. If using an OP FC set up as ComBridge instead of an FTDI, the device name will probably be ttyACM0. In addition to being set up as ComBridge, an OP FC might need to have the correct baud rate set. Use the GCS for that. Do I recall that you need to leave the GCS running to use an FC as a ComBridge?
Once you are in a directory that has both uploader and the firmware you type this (but don't press Enter yet):
./OPUploaderTool -t /dev/ttyUSB0 -p fw_gpsplatinum.opfw
Get ready to plug the GPS "GPS+MCU" port into the FTDI
Press Enter and quickly plug the GPS into the FTDI
Within a few seconds, it should produce a progress bar, if not, ^C and try again.