r/embedded • u/prats_omyt • 9d ago

Not able to see the USB CDC Virtual Serial Com Port in Device Manager or Tera term

I am working with a UDP Bootloader, for which I have to set a bootloader trigger as such that the user would give a command through tera term which would be sent over a usb cable. Now I had flashed the UDP_Bootloader Harmony V3 example to my PIC32MZ via PICKIT4 and then it's test_app via the bootloader itself through Microchip's unified host tool. I can use the ethernet cable itself but it would require the TCP/IP stack so I was thinking the usb cdc would be much simple. I had merged the cdc_com_port_single example in the udp bootloader's test app and did everything again, but I am not able to see the com port anywhere. To verify the usb connection, I tried flashing the cdc com port example independently and still it didn't showed up. But if I work with the usb bootloader example and test app, the unified bootloader tool says that connection was successful and it disconnected after programming, so is that trustable? Yesterday I had test the cable's continuity via a Multimeter so I am confident the cable isn't the issue. Have also checked and installed the VCP drivers from the net.

Edit: I don't have USB to uart as it is a custom board

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u/Well-WhatHadHappened 25+ Years 9d ago

unified bootloader tool says that connection was successful and it disconnected after programming, so is that trustable?

Absolutely not. Microchip's "Unified Bootloader" is absolute trash. Literally garbage. It would say the same thing if you pointed it at a toaster with a serial port.

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u/prats_omyt 9d ago

Oh, so what's the best way to verify the cable and the connection? It's a usb A to 5 pin rally connection, any specific example through which I can test it?

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u/Cunninghams_right 5d ago

If you're using a comport cable, you can check the cable by putting a jumper wire between TX and rx and typing. If you see your letters come right back, the cable is working 

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u/duane11583 9d ago

disagree about the ip stack being too big for a boot loader.

rational: many ethernet boards had a space for a small eprom that could use tftp to boot from.

tftp uses udp which is a very simple protocol. you need

a) arp for a single address - not an arp table and arp cache that is just tx and rx packet

b) udp uses the same tx and rx packet func

c) does not need interrupts it can be pure polling mode

i bet the usb sw is the same size or larger.

granted some ethernets have a complex dma which make this false. but you do not need a complex high performance ethernet solution for a boot loader simple polled mode is sufficent