No mention of Boot0( R19 ) needed to be pulled to 3.3V for programming

[dlarue]

I just looked at my JL1 board and there is no easy way to pull Boot0 on the STM32F103 high on powerup to get it into programming mode( STLink or DFU ). I did trace it to the side of R19 closest to the MPU with the other side of R19 ground. ie R19 is a pull down.

Also, I powered up the USB, applied 3.3V/gnd to the STLink interface which powered the STM32F104 and doing so with Boot0 pulled to 3.3 during power-up I got DFU capabilities over the USB connection.

Without any motors connected the same DFU connectivity could be done by powering the MCU via the 12VDC barrel jack instead of powering via the STLink interface. What this means is you don't need an STLink programmer to program the JL1 but will need to disconnect the motors(for safety).

1. disconnect the 2 motor 4-pin connectors
2. plug in USB cable and see USB0 device created
3. BOOT0: jumper onboard 3.3V(unknown location) to R19 nearest the STM32F103
4. apply 12V power
5. remove BOOT0 jumper
   load DFU and start programming.