Dynamic USB Serial Number (PIC18F4550)

[awmt102]

Thanks for the reply Darrel.

I can see how assigning a serial number on the PC side could overcome this problem but you have to admit its a bit of a bodge and if you end up having to keep a lookup table of handle to serial number then a software crash would lose that information and you would have un-plug and then reattach your devices to re-assign serial numbers - very clunky! For a one off application this might be OK however this device is likely to be used in many different pieces of software in the future and minimising the PC side coding is very desirable.

When you say overwriting the flash and re-enumerating is not worth it which part is not worth it? if its the re-enumerating can I not just write over the flash before calling USBINIT? Or is writing to the flash the hard part?

Thanks

Andy

[Darrel Taylor]

Sure, you could just write the PORTD value to flash on power-up (if it changed). Then when the device connects to the PC ... it will have the new S/N.

But yes ... writing the string to flash IS the hard part, and that would limit you to 256 devices (globally).

Some programmers will allow you to save an incrementing S/N to flash on each program cycle. The meLabs programmer let's you do that. But finding the correct location in flash to put the data is the hard part there. If the program changes, the string location will too.

It's a tough one.
<br>

[awmt102]

OK, I failed to realise that the location in flash will change (although it does make sense now I think about it).

Limiting to 256 devices is no problem, there will never be that many in existence.

I think what I shall do is revert to an earlier version of my firmware that uses an extra byte in the USB Transfers to identify the device.

Thanks for the help Darrel.