Toshiba gigabeat f20 SD card modification
It is possible to put an SD card on a toshiba gigabeat F20 mp3player while using rockbox with one limitation.
It's not possible to access the SD card contents from the mp3player. One has to remove the SD card from the mp3player and store the files and music in some other way. Once the correct files are present on the SD card (GBSYSTEM files , and a complete rockbox installation) the mp3player will boot into rockbox and all files and music will be visible from rockbox. If you try to connect your gigabeat to your computer, no usb drive will be advertised. I guess this is because of some incompatibility with the Cypress EZ-USB AT2 chip on the gigabeat with the CF-SD adapter. Since the gigabeat doesn't use this adapter for accessing the SD card, but instead uses a more direct access, then it works!
My next thing to test is to use a 64GB SDXC card with my gigabeat.