Finalmente descobri que estava emitindo o comando errado no lado do receptor.
O comando de recebimento deve ser: cat < /dev/ttyUSB0 > file_b64
Resumo
Para receber do controle remoto:
Host side | Remote side
|
| #Encode to base64
| cat file | base64 > file_b64
|
| #Send after timeout
| (sleep 10; cat file_b64 > /dev/ttyS0) &
|
#############################################################
### Exit minicom but keep configuration (ctrlA-Z, then Q) ###
#############################################################
|
#Receive file |
cat < /dev/ttyUSB0 > file_b64 |
|
#Decode file |
cat file_b64 | base64 -di > file |