I flashed the device earlier ok with firmware update and then a test blink program ok.
Now I wrote another small blink app and when I try to flash I get the really useful debug info below and have no idea what is happening…
! Serial:
Error writing firmware… Transfer cancelled
undefined
Is the device in Listening mode?
Your user firmware might be interfering with the flashing process. Personally I find DFU flashing much more preferable since it’s a lot more reliable, as well as giving better error outputs.
Hi,
What is the DFU flashing?
So far I am only aware of flash OTA or by serial using CLI.
Thanks
I am not sure why the cli stopped flashing, I ended up using OTA yesterday to upload a couple more changes to my little test code. It would not be so frustrating if the cli at least gave a useful message to explain why it the flash process was terminated. A remark like “undefined” has no meaning to me and does not help me find the issue.
That’s what DFU gives you 
To use DFU you need to put your device in DFU mode, and issue particle flash --usb firmware.bin using the CLI. You’ll need to have DFU-Util installed properly though (which should be done for you when using the Windows installer).
I used the CLi yesterday and received the “unknown” error and termination of flashing.
It was therefore DFU that was giving the useless error message.
You mentioned you used Serial. Serial != DFU The CLI can use either, it’s up to you to decide which one it uses.
I see, I did use DFU to install the latest firmware in the device but then used CLi for flashing new code.
So, If I use DFU mode instead then I will get better error messages?
The CLI can also use DFU, so there’s no separation in that regard.
Indeed it should.
This happened to me when I accidentally compiled for Electron, when I should have compiled for Photon.
// Don’t do this for a Photon…
particle compile electron firmware
particle flash --serial firmware.bin
That is, if you do the above, and try to flash to Photon this error appears:
? Press ENTER when your device is blinking BLUE
sending file: firmware.bin
! serial:
Error writing firmware…Transfer cancelled
undefined