PORTS Forum

Ports and Interfaces => USB => Topic started by: vinoth on March 05, 2012, 06:01:26 am

Title: Change in Input Report descriptor format
Post by: vinoth on March 05, 2012, 06:01:26 am

Hi,
I wanted to know whether a usb device can indicate the host that a particular input report descriptor's format has changed at run time.

For example, Let us say an item-I is part of an input report and the maximum value of item-I is 10. The maximum value is indicated to the host via input report descriptor when the host makes a "Get input Report Descriptor Request".

At run time, let us say the maximum value of  item-I changes to 11. Is there any way to indicate this change in maximum value to host ?

-Regards
Vinoth

Title: Re: Change in Input Report descriptor format
Post by: Jan Axelson on March 05, 2012, 12:24:27 pm

To change the report descriptors, the host would need to re-enumerate the device. However, Windows has been known to "remember" the previous descriptors for a device so re-enumerating wouldn't help.

Better to use the maximum value the HID will need in any situation. If you need to send additional information, for example, "ignore values > 10" or whatever, you can do that in a separate vendor-defined report item or even a separate report.

Jan

Title: Re: Change in Input Report descriptor format
Post by: vinoth on March 06, 2012, 12:50:03 am

Hi Jan,
Thanks for the clarification.

-Cheers,
Vinoth