The difficulty is that most boot loaders have commands to download new firmware into ram and then write it into nand or nor flash memory, but not commands to upload the content of flash memories to a serial port or SD card. - This helps prevent unauthorized duplication or reverse engineering...

And that's after you have found and soldered wires to the serial port so that you can enter boot loader commands

And trying to use the JTAG port is even worse.
pholy