MSP430F5521 - USB Virtual COM port in Windows

Nick Petrescu

Other Parts Discussed in Thread: MSP430F5521

Hello,

Does anyone know how to prevent the CDC USB drivers to assign a new COM port number when similar devices are plugged and then unplugged. For instance I have three identical devices built with MSP430F5521 and when I plug them in (one at the time), Windows will assign consecutive COM ports to them. That is not a problem when there are just three but when you have over 100 this becomes a nightmare and Windows just simply remembers them and deleting the unused ports becomes extremely cumbersome if there are a lot assigned as they can only be deleted one by one.

Trying to automate testing such devices is basically becoming an impossible task unless I use a static COM port assignment scenario.

So is there a way to tweak Windows to think I am plugging in the same device so it only assigns the same COM port all the time? Someone told me that some other chips from Silicon labs offering that capability.

Thanks a lot

over 8 years ago

0 Clemens Ladisch over 8 years ago

Guru 243220 points

When devices have a unique serial number, Windows remembers them. (This is considered a feature.)

Set USB_STR_INDEX_SERNUM to zero.

0 Nick Petrescu over 8 years ago in reply to Clemens Ladisch

Intellectual 470 points

Would be in Win Registry or do I need to enter it in the Win Environement ? Thanks for the quick reply!

0 zrno soli over 8 years ago in reply to Nick Petrescu

Guru 33653 points

TI USB stack by default generate serial using unique Die / Wafer / X / Y ID. Fix serial to zero (or any other constant) inside TI USB stack for all devices, and Win will use same COM port for all.

0 Nick Petrescu over 8 years ago in reply to zrno soli

Intellectual 470 points

I'm not entirely sure how and where I need to apply this fix. If someone can elaborate, perhaps with a step by step or at least some pointers to where in Windows, please, that would be awesome! Thank you all!

0 Clemens Ladisch over 8 years ago in reply to Nick Petrescu

Guru 243220 points

The USB descriptor tool generates the following code in USB_config\descriptors.h:

// If a serial number is to be reported, set this to the index within the string descriptor
//of the dummy serial number string.  It will then be automatically handled by the API.
// If no serial number is to be reported, set this to 0.
#define USB_STR_INDEX_SERNUM  3

You need to recompile and re-flash your device's firmware.

I do not know of any way to make Windows ignore the serial number without changing the device.

0 zrno soli over 8 years ago in reply to Nick Petrescu

Guru 33653 points

It is not in Win, it is inside your firmware (CDC part). Find device descriptor inside TI USB stack, and how serial is updated / generated on-the-fly.

0 Nick Petrescu over 8 years ago in reply to zrno soli

Intellectual 470 points

This worked well; thank you all for your help! So what I did was to change the #define USB_STR_INDEX_SERNUM from 3 to 0 setting in the descriptors.h descriptor file, re-compiled the firmware and now all my devices are using the same COM port. Love this forum!

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MSP430F5521 - USB Virtual COM port in Windows