I had another opportunity to check out another USB WiFi adapter with the RPi. My son brought it to me this morning and asked me if I could fix it. One of his friends had given it to him and said it would only work for a few minutes before it stopped working and that if I could fix it then my son could keep it. He handed it to me and then headed out the door to school.
I inserted it into my Pi and it instantly triggered a reboot, something I was able to reproduce without fail. Not a good sign. However, once the reboot was completed, I logged in, checked the output from dmesg and found that the adapter was recognized.
[ 3.173272] usb 1-1.3: new high-speed USB device number 4 using dwc_otg [ 3.296293] usb 1-1.3: New USB device found, idVendor=050d, idProduct=945a [ 3.305735] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 3.315539] usb 1-1.3: Product: Belkin USB Wireless Adaptor [ 3.323572] usb 1-1.3: Manufacturer: Manufacturer Realtek [ 3.331420] usb 1-1.3: SerialNumber: 00e04c000001 [ 11.123664] r8712u: module is from the staging directory, the quality is unknown, you have been warned. [ 11.468760] r8712u: DriverVersion: v7_0.20100831 [ 11.533774] r8712u: register rtl8712_netdev_ops to netdev_ops [ 11.542073] r8712u: USB_SPEED_HIGH with 4 endpoints [ 11.617524] r8712u: Boot from EFUSE: Autoload OK [ 12.392847] r8712u: CustomerID = 0x0000 [ 12.399176] r8712u: MAC Address from efuse = 08:86:3b:24:1c:94 [ 12.407487] r8712u: Loading firmware from "rtlwifi/rtl8712u.bin" [ 12.419393] usbcore: registered new interface driver r8712u [ 25.973680] r8712u: 1 RCR=0x153f00e [ 25.974422] r8712u: 2 RCR=0x553f00e
As I had used this Pi to write my article on the Linksys AE1000 USB adapter I didn’t have to do any additional configuration and the adapter came up on the network without a problem.
I went and took a look at the log to see if there was any useful information regarding the sudden reboot but there was none to be found. As quickly as the reboot happened, I’m not surprised there were no log entries. I did note the message stating the r8712u module is from the staging directory and wondered if it was just a bug causing the reboot but I ruled that out as you will see below.
From one of my other systems I ran a continuous ping against it for an hour as a good initial test. There were no lost packets. Then I ran ping with the -f (flood) flag for a minute or so and didn’t see a significant number of timeouts. There were a few so I ran a ping flood against one of my other wireless devices and the results were comparable.
I left the adapter plugged in for a while and ran some more tests and it still seemed to be stable. Now it was time to see what happens when I unplug it.
[ 845.393778] usb 1-1.3: USB disconnect, device number 4
The disconnect was logged and the Pi kept running. The adapter was quite a bit warmer than I expected. I suspect that the problem my son’s friend was experiencing with it may be due to overheating. If any readers have had a similar experience then please share it in the comments. I would like to try and determine if this is an issue with this individual adapter itself or if it’s a common one across the board.
Back to the reboot issue. I decided to check if the problem was due to a voltage drop so I grabbed the DMM. I didn’t see any voltage drop, just the increase when the system rebooted before the ports were powered up. I also did the same with my Linksys adapter and found it caused a reboot as well. I swapped out the power supply from the 700mA one to a 1A one and tried both again. The Linksys came up just fine but the Belkin caused another reboot.
Next, I hooked up my powered USB hub and plugged both adapters into it in turn and both came up just fine. No reboots.
I suspect the cause of the reboot is the current required when the device powers up after it is inserted. I can’t say for certain as I am unable to measure that.
Anyhow, here’s my take on the Belkin. I think it may be a suitable choice as long as you don’t plan to insert it into one of the onboard USB ports while the system is running. If you do need to plug/unplug it while the system is running then use a powered hub. I also wonder about the operating temperature of the Belkin and if it is a cause for instability.
Please leave your comments and let me know what you think!
Update: For those of you who are interested, here are the voltage readings for the Belkin and the Linksys.
Belkin – no network traffic – 4.87v
Belkin – ping flood – 4.85v
Linksys – no network traffic – 4.86v
Linksys – ping flood – 4.84v
No adapter – 4.95v