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RTOS/AM3356: Check USB power negotiated with host in TI-RTOS

Han Hoekstra
Prodigy 230 points
Part Number: AM3356

Tool/software: TI-RTOS

Hello All,

We are developping an application running on a TI AM3356 using TI-RTOS. Our device will have a USB port, which is used for communications to a USB host, but also to supply power. I have the USB mass storage device example working in my application. But now I have a question regarding USB power. In the structure defining the operating parameters for the USB device I have set 'usMaxPowermA' to 500, so during USB enumeration it will tell the host we want to draw 500 mA from the USB port. But how do I check that the host has confirmed the use of 500 mA ?

This is important for us, because when we detect that we are drawing power from the USB port, we will limit power consumption to fall within the 100 mA limit during startup. But we want to increase that to 500 mA as soon as we know that the host has confirmed that we can do this. Where can I check that the host has confirmed our request for 500 mA during the USB enumeration ? One of our requirements is to be USB 2.0 compliant, so we must comply with this 100mA / 500 mA current limit.

I have not been able to find anything on this topic via google or on the forum here. So if there is anyone that can help me with this, I would really appreciate it !

  • 0
    TI__Guru* 95265 points
    Hi,

    We have a field called usMaxPowermA and used in USBDMSCCompositeInit() to negotiate the USB power supply from host side. I thought this is a USB protocol question, but not TI software. Let me check if we know this.

    Regards, Eric
  • 0
    TI__Guru*** 125316 points
    Hi Han,

    Eric is correct. This is all defined in the USB 2.0 Specs.
    If my memory is still good, I believe the USB device can only draw up to 500mA when it is already in CONFIGURED state during enumeration. Please double check with the USB Spec. So your USB device driver should tell when to increase power consumption.