There are any API for access the content of SD Card by cable?

You can stream the content of SD Card to the serial port so you can capture the file with your own program.

You can use Bluetooth (COM Port) in the PC, then use this protocol for request the file you want to extract (or delete it or just report file list). This is the protocol used by the programs "Smart OS Config" and "North SD Downloader"

https://www.dropbox.com/s/svqtcr3f9y80yvu/SmartOS%20Protocol%20V2.pdf?dl=0

Later, you can test the same by serial cable. For this you have two options:

- Setup the unit so the "Mode Config" is done by cable, so not only the download of file will be by cable, but also the "Smart OS Config" will need accesed by USB cable because Bluetooth will be off. Most Android Tablets have USB OTG, so you can connect by USB and use the "Smart OS Config" for setup the unit later. Or, if not, if you cannot use Smart OS Config over USB cable, then use the "Smart OS Config PC" for send a "Factory Reset" and recover the control over Bluetooth (this Smart OS Config PS is deprecated, but for some settings is ok). Or just send by RealTerm the sequence to do a "Factory Reset"

- Use the mode "Download by Cable" (the last mode on hte list "Receiver Mode")

Both above options are configured by the "Smart OS Config"

NOTE: By "serial cable" I mean interface to pins 2/3 at 11500 using the appropiate TTL3.3V or RS232 (depend of RTKITE flavour) to USB converter