3 Replies Latest reply on Jul 23, 2016 10:06 AM by dmitry.kozhevnikov

    The max power of Configuration Descriptor is not work

    wei.liu

      hello everyone.

         

      devices:cyusb3014(FX3).

         

      we desinged a board( the cy3014 is be described composite device(UVC + CDC) ),the max power it need is more or less 600mA when it works,but the question is when i set the max power of Configuration Descriptor to 0x64(usb3.0 will be 800mA > 600mA). at the same time it just use the USB3.0 power to supply, in this case the composite can be enumerated in PC. but when i let it work,this composite device will be disappear;so i must use external power to supply this board,it can able to work normally.which means the max power i set in Configuration Descriptor is not work.

         

      And when i configure the max power to 0x0c(usb3.0 will be 96mA).in this case,I let my board work using USB3.0 power supply and external supply, i find the electricity(external supply) is 0.36A and electricity(usb3.0 power supply) is 0.21A .this mean the total electricity is 0.57A,but the question is the value of electricity(usb3.0 power supply)--0.21A is much bigger than the max power(96mA) i configure, which all mean the max power i configuration in Configuration Descriptor is not work.

         

      hope someone can help me to solve my doubt(usbDescriptor is attached).

        • 1. Re: The max power of Configuration Descriptor is not work
          nisa

          Generally,  the device will work even if it is drawing more current than what mentioned in the configuration descriptors, unless the total current from the hub exceeds the max current from the hub. The hub/host will  check configuration descriptors power setting during the configuration to see if it can support that much current.

             

          Have you tried to set the bmaxpower to max supported and see?  If you have UVC+ CDC, please stop UVC streaming and see if CDC transfers are working? Is it like UVC is taking most of the current, so that CDC transfers are not supported?  You can create a tech support case if the problem persists

          • 2. Re: The max power of Configuration Descriptor is not work
            wei.liu

            thanks a lot.

               

            I test as you told me ,the CDC can work.but when i let the FPGA and Cy3014 work, the composite device will be disappear,which means the composite device cannot be enumerated in PC, it is the problem that the power cannot let the composite device work.I test my board,the power it need is more or less 600mA,and i configure the max power to 900mA (usb3.0).this means the max power i configuration in Configuration Descriptor is not work.

            • 3. Re: The max power of Configuration Descriptor is not work
              dmitry.kozhevnikov

              More than the initial hub/host configuration you've mentioned, does the bMaxPower value have any additional practical sense in USB System of linux/windows? How that configuration descriptor field is controlled by a host?