USB Host HID Class Example for LPC2468

Tsuneo,

Thank you for your reply -- I'd like to follow your suggestion of getting NXP Host Lite to work for my purposes.

The device I am connecting is specific, in fact it is another LPC2468 running a modified version of Keil's HID Client example. This device has an interrupt IN endpoint and an interrupt OUT endpoint (both endpoint 1) that I would like to use for transferring the data. The IN report and OUT report size are each 64 bytes (and I do not need a feature report). The end point descriptors request to be polled every 8ms.

Is there any chance you can give me some guidance on modifying NXP Host Lite to communicate with this device? It seems like the main task is to add the support of interrupt transfers - as it looks like Host Lite is setup only for Control and Bulk transfers.

I realize that it may be too much for me to ask you to tell me literally what to modify in Host Lite, but maybe you could suggest something of a check list of items that I must add/modify? (Certainly, if you feel like typing in some literal changes, I would appreciate that - whichever is more practical for you)

A couple questions:
1) For the Interrupt transfers, do I have to set up a timer to that asks for an IN report every 8ms -- or is this something that I can configure the Host Interface to do automatically?

2) Is the polling interval a hard and fast rule, or is it more of a suggestion? (ie, if the device requests to be polled every 8 ms, but I find this to be too big of a performance drag on the host, can I decide to poll it every 16 ms?)

Thank you for any guidance you have the time to give!

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Tamir, I am glad to hear that you have put in a request to Keil asking for more USB Host examples.

-Eric

Tsuneo,

Thank you so much! This is really great.

-Eric

Tsuneo,

Your advice has been great. I have things up and running with Interrupt transfers.

However, I am noticing a strange problem that occasionally occurs. My interrupt IN endpoint stops working, but my interrupt OUT endpoint continues to operate. What I mean by not working, is that the host controller stops servicing the endpoint. The IN endpoint HALT bit and SKIP bit are both not set. TailTd != HeadTd, and yet the transfer descriptor is not serviced. Meanwhile, every time I attached a TD onto the OUT endpoint, it is immediately serviced. Is there a control register or bit somewhere that could cause this problem?

Here are the register values for my IN endpoint (taken in debug mode when the IN endpoint stopped being serviced):

Control = 0x00401081
TailTd = 0x7fd00160
HeadTd = 0x7fd00150
Next = 0

Register values for the TD being pointed to by HeadTd (taken in debug mode when the IN endpoint stopped being serviced):

Control = 0x00100000
CurrBufPtr = 0x7fd00400
Next = 0x7fd00160
BufEnd = 0x7fd0043f

Also, I have verified that the Interrupt Table in the Hcca is correct:

IntTable[0] = &ED_IN
IntTable[1] = &ED_OUT
IntTable[8] = &ED_IN
IntTable[9] = &ED_OUT
IntTable[16] = &ED_IN
IntTable[17] = &ED_OUT
IntTable[24] = &ED_IN
IntTable[25] = &ED_OUT

This problem seems to happen when I disconnect the USB cable during when a transfer is in progress. When I reconnect the cable, if the problem is going to happen, the IN endpoint will work for a few TDs and then stop. Once the problem has happened, it doesn't matter if I disconnect and reconnect the cable -- the problem will occur again. Furthermore, if I power-cycle the USB host, the problem does not go away. HOWEVER, if I power-cycle the client, the problem does go away.

Both the client and the host are running on an LPC2468.

Any thoughts would be greatly appreciated!

Thanks,
Eric

Ah, okay, so I determined the problem: my client wasn't sending data (oops!). But this raises an interesting question:

My understanding of the USB OHCI spec is that regardless of if a periodic (interrupt) IN endpoint receives data, it's TD will be processed, declared completed and placed on the done head. (ie, my understanding was that as soon as the Host Controller gets to servicing the periodic IN endpoint, it attempts a read from the USB client, and then regardless of whether or not the client had data to send, it would retire the TD to the Hcca->Done list).

However, what appears to be happening is that the Host Controller does not decide retire the TD to the Hcca->Done list until some data actually comes in. So, since my USB client had no data to send, it appears that the IN TD was not being placed on the Hcca->Done list.

Is this the way the OCHI USB HC is supposed to behave?

Thank you,
Eric