I spent a week developing software on my mkrzero. Today the USB port quit working after I tried to upload a new program. Windows 10 did not recognize the USB port. However if I double pressed the reset port twice, I got yellow lights and Windows 10 recognized this USB port as a bootloader port with different Com number.
My guess is that the bootloader has been damaged. Is it possible to restore the original bootloader of the mkr zero board, by using the PC and the USB port in bootloader mode?
If not, I did not see any JTAG pins on board. Please advise me on what to do.
If this is a redundant post, please forgive me.
Thanks
Glenn
Hi Glenn,
My guess is that the bootloader has been damaged.
The bootloader hasn't been damaged, as what you're describing is normal operation for the MKR Zero. It just means your sketch has crashed for whatever reason. After a double tap of the reset button just select the new COM port and upload as normal.
While your sketch is running, the MKR Zero's is checking the native USB port behind the scenes. If the COM port is switched to a baud rate of 1200bps by your host computer, the microcontroller goes into bootloader mode ready to receive a new code upload. In this way, automatic reset and uploads can be performed. If however your sketch crashes, there's no way the microcontroller can perform the upload, therefore in this instance, it's necessary to double tap the reset button to manually place the microcontroller in bootloader mode.
Native USB microcontroller boards, such as the MKR Zero, behave somewhat differently from those with a USB to Serial chip, such as the Uno, Mega, etc... Boards with the USB to Serial keep the COM port open continously and have more robust and more resilient feel.