Hi Everyone: Thanks TK for the suggestions.
press & hold the blue button on the STM32F4DISCOVERY board, and then shortly trigger the black button (to reset the device)
Keep the blue button pressed! This enforces bootloader mode.
That happens OK when using the USB interface to MIOS Studio 2. However, with the MIDI interface, I get the following results:
Check query (blue button still pressed) - does this work?
No. The left panel shows “No response from core”
Upload a firmware (blue button still pressed) - does this work?
No. This message is returned: “WARNING: No response from core. Please reboot . . .”
Release the blue button after firmware upload so that the application will be started.
The previous program is started.