Do I need FAT on both ends of a USB link?

Question

I have a product consisting of two boxes, both running an RTOS (not picked yet, say FreeRTOS):

Box A will have:

• an SD card and a FAT stack
• an "external" USB device port with MSD to allow PC access to the SD card
• "internal" USB device port to Box B with MSD

Box B

• an "internal" USB host port to Box A with MSD

QUESTION: do I need a FAT stack in Box B to be able to access the SD card in Box A?

I realize this is a very basic question but I have not been able to find the answer anywhere. Thank you

Answer 1

As it turns out you do not need FAT on both ends. You need it at the Host end not the Device end. MSD takes over the SD Card at a low level so the file system is actually on the Host side. The way to access storage being managed at the Device end is to use MTP instead of MSD.