SD card support

[stepansnigirev]

TODO:

• [x] SD card for key storage #83
• [x] Load / save PSBT transactions #130
• [x] Import / export wallet in our format (descriptor and name) #130
• [ ] Import / export wallet in CC format
• [ ] Export / import seed in encrypted form

[stepansnigirev]

Partially solved with #83 , for now only for key storage. But looks like all the problems are solved so we could load PSBTs from SD card as well.

[SaroC]

Issue:

• Initial FW initial_firmware_v1.8.3.bin flashed with st-flash write ~/development/specter-bins/initial_firmware_v1.8.3.bin 0x8000000
• If I boot the device simply (without a SD card inserted into the socket) all works properly I insert the PIN and the OS show me the menu.
• If I boot the device with a SD card into the socket (FAT formatted)...After that I insert my PIN I receive the follow output: Error! Somenthing unexpected happened... Traceback (most recent call last): File "specter.py", line 76, in handle_exception File "specter.py", line 156, in main File "specter.py", line 186, in initmenu File "keystore/sdcard.py", line 110, inis_key_saved File "platform.py", line 95, in mount_sdcard OSError: [Errno 19] ENODEV

The 32GB SD card was formatted with Win (FAT32 with 16kB allocating size) first and also with Linux's mkfs program (with -t vfat argument). The SD card was used with and without file inside in. If I remove the SD card, also while the device is in on state, the FW works properly again showing me the menu again. Seems that the presence of the SD card is enough to cause the error.

Any suggestion? maybe the size of SD card could be the root cause? a smaller one could fix the issue? Many Thanks for the support.