I am missing something, I know it!

[st2000]

Hi...

I confess:  I'm new to USB (I've done the Microchip USB peripheral class if that counts!).  And I'm really new to USB host coding. [Note, I do have a brand new copy of Jan's book!  So I am set for any of this "Look on page 256 before you ask that again!".]

Where I'm at:  I have the Microchip Explorer16 board running Microchip's USB thumb drive host demo code (yea!). And I have been able to transplant that code onto our hardware platform to repeat the feet (yea again!).  But I think this is simple stuff (mainly because it's "canned" software that doesn't need much "massaging").

There is a media player on the horizon.  We would like to send it new media from time to time but expect it to store files locally like a mass storage device.  We would also like to control it.  Simple commands like "start playing file <name>", "stop" and "are you done yet?".  So we are thinking "let's put a USB interface on it"!  But what will this device look like?  Will it look like a mass storage device?  Or like some sort of HID.  Remember, we want to not only load it up with media but also control it.  Maybe it needs to be a "compound device".  Or maybe we can do all that control stuff and stay inside the definition of a mass storage device.

This is what I am missing, the knowledge needed to ask this question in the right manner.  I am sure a USB interface can do all this and more.  But I am not sure how to go about building the device and programming the host to do it.

Any suggestions which way to go from here would really be appreciated.

-thanks

[Jan Axelson]

Use a mass-storage interface for storing files and a HID interface for control. A device with multiple independent interfaces is a composite device. Microchip has a HID + MSD example.

Jan

[st2000]

Thanks Jan for the pointer to the MC sample/example project.  I want ask more questions but will contain my self and do a bit of reading first... 

well...,

ok,

I'm going to ask one question...

... if you want to do something a bit custom w/the, hummm, HID side of a composite device.  Like control some buttons or something, in addition to working with the other composite device (the mass storage device).  How would you going about that?  I mean WRT the USB stuff (I know all about the electronic side, no help needed there).  Like, where would you start tinkering with the software that controls & queries the HID device.

-thanks

[Jan Axelson]

All HID data travels in reports. You can define the reports any way you want. For example, the host application can display a control panel and send data to indicate what buttons the user clicked. Take a look at my HID host application, or Microchip's.

Jan