Objective Development Forums

I'm building the simplest AVR-USB circuit I can, using the atmega324p and based off of the powerSwitch demo, running completely on external 5v power. When I connect it to linux, I get

Feb 20 17:25:02 foo kernel: [66496.580000] usb 1-5: new low speed USB device using ohci_hcd and address 29
Feb 20 17:25:02 foo kernel: [66496.760000] usb 1-5: device descriptor read/64, error -62
Feb 20 17:25:02 foo kernel: [66497.044000] usb 1-5: device descriptor read/64, error -62
Feb 20 17:25:02 foo kernel: [66497.324000] usb 1-5: new low speed USB device using ohci_hcd and address 30
Feb 20 17:25:03 foo kernel: [66497.504000] usb 1-5: device descriptor read/64, error -62
Feb 20 17:25:03 foo kernel: [66497.788000] usb 1-5: device descriptor read/64, error -62
Feb 20 17:25:03 foo kernel: [66498.068000] usb 1-5: new low speed USB device using ohci_hcd and address 31
Feb 20 17:25:04 foo kernel: [66498.476000] usb 1-5: device not accepting address 31, error -62
Feb 20 17:25:04 foo kernel: [66498.652000] usb 1-5: new low speed USB device using ohci_hcd and address 32
Feb 20 17:25:04 foo kernel: [66499.060000] usb 1-5: device not accepting address 32, error -62

My schematic is here: http://i248.photobucket.com/albums/gg19 ... 0109_2.jpg - the actual circuit has a connection from the D+ line to PD2/INT0, I just forgot to draw it here. Also in this schematic is what I believe is the USB "B" type socket pinout. The diodes are 1N5226B 3v6 zeners, the caps 22p ceramic, and the crystal is a 12Mhz (FOX120-20)

Here are two pictures of the circuit: an overview and a detail of the USB section. http://i248.photobucket.com/albums/gg19 ... G_0107.jpg and http://i248.photobucket.com/albums/gg19 ... G_0108.jpg

The software is the stock powerswitch software, with USB_CFG_IOPORTNAME B, USB_CFG_DMINUS_BIT 0, and USB_CFG_DPLUS_BIT 1, makefile has DEVICE set to atmega324p, uploaded via AVRDUDE. The 12 Mhz crystal has been fused and confirmed to be working through LED timing tests.

I think I did everything right - did I miss something?

Since the device shows up with different addresses in the log file within a period of 2 seconds, I suppose that enumeration fails.

Since you have made sure that the AVR runs on 12 MHz, the most likely causes are missing zener diodes in 5 V designs or an incorrect initialization of the pins involved for USB. All pins must be configured as inputs without internal pull-up resistor.

As far as I remember, the "new device" message occurs even for a single pull-up resistor on D-.

christian wrote:Since you have made sure that the AVR runs on 12 MHz, the most likely causes are missing zener diodes in 5 V designs or

I've got the zeners in the circuit and in the linked schematic, I think - am I missing something?

christian wrote:an incorrect initialization of the pins involved for USB. All pins must be configured as inputs without internal pull-up resistor.

The PowerSwitch code handles this, doesn't it?

#define USBMASK ((1<<USB_CFG_DPLUS_BIT) | (1<<USB_CFG_DMINUS_BIT)) /* mask for USB I/O bits */

DDRD = ~(1 << 2); /* all outputs except PD2 = INT0 */
PORTD = 0;
PORTB = 0; /* no pullups on USB pins */
DDRB = ~USBMASK; /* all outputs except USB data */

Yes, this code is intended to handle this. However, it has been developed for the 2313 and it may not be suitable for your pin assignment and AVR type.

Even wierder, the circuit works fine - as long as i work from bus power and my AVR ISP Mkii programmer is also attached - to the same computer.

If the programmer and device are plugged into different computers' USB ports, it doesn't work. Ground has good continuity from avr-usb plug... Why would it care about the programmer?

Mystery solved! I need to remember: anytime you see random behavior, first look for open grounds, then look for noise.

At the suggestion of eric_j in #avr on freenode, I added a pair of caps, a 47 uf electrolytic and a 0.1 uf across the power near the avr. Suddenly, it all works - both on and off bus power, with and without the programmer attached.

The programmer must have had enough capacitance to clean up the noise - once I added my own, the circuit works! Here is the final version, for anyone else that might be having a similar problem.

http://i248.photobucket.com/albums/gg19 ... switch.png