Hi, First of, I am very new to USB. My project is wireless related (not USB) and I am in the process of testing the Linux (kernel 2.6.16.15) wireless performance using wireless usb devices. I use D-Link USB (54Mbps) device as my testing device. The max performance of wireless transmission is roughly around 25Mbps. I am currently using 2 wireless channels (chan 6 and 11) without encryption. My tests are as followed.
Using 4 PCs called PC1, PC2, PC3, and PC4, PC1 and PC2 are connected with each other in Ad-Hoc mode channel 6. PC3 and PC4 are connected using channel 11 also Adhoc mode. The performance is as expected. Each pair is transmitted at expected speed around 20-25Mbps. I use "ttcp" to test its speed. This test is to ensure that channel 6 and 11 do not interfere with each other and they seemed that they do not interfere with each other. But when I used 2 PC's with 2 channels per PC. again in Adhoc mode and ran ttcp on both channels simultaneously, the speed of each channel went down by 1/3 to 1/2 of the expected speed. I suspect that it is USB related. BTW, I don't have any other devices running on the USB port, just the 2 wireless USBs. So I dig into the D-link USB driver (open source by Ralink) and found that it uses Bulk transfer mode. And the code seems to be reasonable. It calls "usb_fill_bulk_urb" with "usb_sndbulkpipe" and "complete" callback function and then calls "usb_submit_urb" to do the transmit. When "complete" callback is called, the transmit procedure is repeated if there are still packets in the queue. I check the "wMaxPacketSize", it is already set to 64 when the probe function is called. Is there anything that I could do to enhance the performance. BTW, I don't have USB analyzer to look at the USB bus. Any suggestions are appreciated. Hopefully, there is some place that I could tweak in the kernel to improve the performance. Thanks in advance, Adisorn. ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
