I realize this issue comes up periodically. I have a situation that statistically is impossible but yet is happening.
My test program is "blink without delay" with nothing but the programming cable connected to the Pro Mini boards.
I have a windows 11 pc with IDE 2.3.6, I've been working with a SAM21D and needed to switch back to a Pro Mini. The below test conditions have worked many many many times on the Win11 pc but with older IDE's (but wait, see below)
I connect one of my many Pro Mini's and start to download and received the Arduino equivalent of the Blue Screen to Death namely the "cannot sync..."
I am using a DSD FTDI programmer I'll call NEW. Has a genuine FTDI chip (based on the FTDI test program. My FTDI_old is a known chip clone.
If you have an Arduino UNO, try to upload BWD, this should once again give you some confidence.
If the UNO fails, sit down with a warm glass of Frangelico.
Have you done loop back testing ?
Have you tried a different USB port on the desktop ?
OK, then that disproves my hypothesis. The "soft bricking" caused by the board going into an endless reset loop if you upload a sketch that triggers a watchdog timer reset is specific to the Pro Mini's "ATmegaBOOT" bootloader, but does not occur when using the Optiboot bootloader.
No UNO.
Loop back Test, Yes, seems to work fine (used the IDE monitor window)
Always the same USB port on the PC but I assumed when I tested with my laptop that would qualify as a different port and different cabling from cpu to programmer.
BTY Just before I switched to the Pro Mini I was programming a SAMD21 over and over.
Had 2 x 5V and 1 x 3.3v. Made sure both adapters when tested were at the right voltage.
I had a similar situation recently, and the problem turned out to be a bad cable. All five wires were there, but there was some sort of intermittent break inside the cable. I binned that cable and no problems since.
Thanks for the response, I figured going to the laptop which uses different cables would be enough. But today I'll going to change the cable and port on my desktop, that is after saying a prayer and sacrificing a coffee,
What was the exact procedure you followed to install it?
I ask because I see from the screenshot you shared that the upload baud rate was 57600. The most simple way to install Optiboot on an ATmega328P@16 MHz Pro Mini would be to select Tools > Board > Arduino AVR Boards > Arduino Uno from the Arduino IDE menus and then performing a "Burn Bootloader" operation. After that, you would need to use that same "Arduino Uno" board selection when using the Pro Mini, since the bootloader binary is compiled for an upload baud rate of 115200.
It is possible to install an Optiboot bootloader compiled for 57600 baud, as is easy to do using MiniCore, but that isn't the default for 16 MHz boards even when using MiniCore so even with MiniCore it is something you would have needed to chose manually.
If one of the "5V" Pro Mini is the one with the Optiboot bootloader, select Tools > Board > Arduino AVR Boards > Arduino Uno from the Arduino IDE menus and then try an upload to that board.
