Mikhail updated his GBA GPS Mapping Receiver. Here is what the author says:

I have added two not built-in in GBA communication speeds: 1200 and 4800 by custom reading algorithm in the general mode of the GBA link port. Now almost all available sensors/boards/receivers can be used with GBA GPS. Also, I changed scrolling algorithm (to make it smoother) and add ‘settings”menu to the ROM maker program.

http://www.msh-tools.com/GBA/gbagps.html