Objective Development Forums

Re: Lost connection with PC: any way to restore?

2009-10-07T10:43:51+02:00

I have read about this when doing support. Somebody found out that the program was executing normally, but the I/O registers were reset to their RESET state. I have not verified this myself, so it may have been some other unexpected behavior.

On the other hand, I have seen lots of EMI problems with the AVR myself, especially with V-USB. Probably because a long cable is directly connected to I/O pins.

Statistics: Posted by christian — Wed Oct 07, 2009 10:43 am

Re: Lost connection with PC: any way to restore?

2009-10-07T02:25:11+02:00

christian wrote:... Analysis has shown that the AVR itself performs kind of half of a reset. Some parts of the chip go into reset status, others don't. I have seen this even on projects without USB connectivity.

Sorry this is drifting slightly off-topic, but I was wondering if there were any resources to look into about this sort of "half-reset" problem? Thanks so much!

Statistics: Posted by Alan Chatham — Wed Oct 07, 2009 2:25 am

Re: Lost connection with PC: any way to restore?

2009-10-04T11:39:44+02:00

If your main() routine begins with a usbDisconnect() which lasts for some time (all our examples do that), then I don't see a difference to initiating the disconnect somewhere during runtime.

If your main() does not do that, the host won't know that you had a reset. The USB driver's usbDeviceAddr variable is reset to 0, but the host tries to reach it under the address which was negotiated before the reset.

Statistics: Posted by christian — Sun Oct 04, 2009 11:39 am

Re: Lost connection with PC: any way to restore?

2009-10-03T19:42:22+02:00

christian wrote:Why should this prevent the disconnect/connect sound? A watchdog reset also triggers a disconnect. If it does not, there's a discrepancy in the host's notion of the USB ID and the device's notion.

You should be able to prevent EMI problems with a (very) good board layout.

Dear Christian, I am not expert on USB however the solution I adviced somehow worked for me. Could you explain little more what may cause "discrepancy in the host's notion of the USB ID and the device's notion." Actually after reset of device I can still read my usb parameters corretly and windows does not give plug - unplug sound.

Statistics: Posted by Guest — Sat Oct 03, 2009 7:42 pm

Re: Lost connection with PC: any way to restore?

2009-09-28T12:00:35+02:00

Why should this prevent the disconnect/connect sound? A watchdog reset also triggers a disconnect. If it does not, there's a discrepancy in the host's notion of the USB ID and the device's notion.

You should be able to prevent EMI problems with a (very) good board layout.

Statistics: Posted by christian — Mon Sep 28, 2009 12:00 pm

Re: Lost connection with PC: any way to restore?

2009-09-27T22:38:34+02:00

I tried to use watchdog reset to init firmware when usb connection is broken. I will check the connection periodically from host software and clear a flag. If flag is not cleared IC will get into watchdog reset. This does not cause re-connect with usb hence no sound for disconnect - connect of usb device. Any idea about this solution is very appreciated.
Saltuka

Statistics: Posted by Guest — Sun Sep 27, 2009 10:38 pm

Re: Lost connection with PC: any way to restore?

2009-09-27T17:33:10+02:00

Reseting USB fixes connection problems but connect- disconnect sound in windows is an isue. My quesiton is: Is there a way to
disable this sound only for a given VID/PID USB device in Windows.

I am using win - usblib as USB driver. May be there is a way to fix this isue from driver.

Best regards
saltukasaltuka

Statistics: Posted by Guest — Sun Sep 27, 2009 5:33 pm

Re: Lost connection with PC: any way to restore?

2009-09-23T04:18:40+02:00

Just an idea,

Periodically read a specific message from AVR-USB device. In switch : case of this message refresh a timer. If timer overflows reset the chip.If USB device
always works fine the timer should not have chance to overflow hence no reset occurs.

Statistics: Posted by Guest — Wed Sep 23, 2009 4:18 am

Re: Lost connection with PC: any way to restore?

2009-09-22T10:30:34+02:00

I can confirm that EMI (Electro Magnetic Interference) is a problem with AVRs. Switching an inductive load can cause the PC disconnect. Analysis has shown that the AVR itself performs kind of half of a reset. Some parts of the chip go into reset status, others don't. I have seen this even on projects without USB connectivity.

You can brute-force work around the problem by performing the USB disconnect when you suspect a problem.

Other than that, all measures which reduce EMI help. But this is a very complex topic.

Statistics: Posted by christian — Tue Sep 22, 2009 10:30 am

Re: Lost connection with PC: any way to restore?

2009-09-03T11:47:15+02:00

I don't know how clean is this workaround, but at least it works for me.
I just run this every 10s:

Code:

USB_INTR_ENABLE &= ~(1 << USB_INTR_ENABLE_BIT);
usbDeviceDisconnect();
_delay_ms(500);      // or some other sort of delay
usbDeviceConnect();
USB_INTR_ENABLE |= (1 << USB_INTR_ENABLE_BIT);

Statistics: Posted by AntonG — Thu Sep 03, 2009 11:47 am