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[Discuss-gnuradio] USB2 high speed vs. full speed.

From: Berndt Josef Wulf
Subject: [Discuss-gnuradio] USB2 high speed vs. full speed.
Date: Sun, 13 Feb 2005 23:41:24 +1030
User-agent: KMail/1.7.2


The following are the reported devices and their configuration after loading 
the firmware and fpga:

Reported devices by kernel during at bootup

hci0 at pci0 dev 29 function 7: Intel 82801DB USB EHCI Controller (rev. 0x01)
ehci0: interrupting at irq 11
ehci0: EHCI version 1.0
ehci0: companion controllers, 2 ports each: uhci0 uhci1 uhci2
usb3 at ehci0: USB revision 2.0
uhub3 at usb3
uhub3: Intel EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub3: single transaction translator
uhub3: 6 ports with 6 removable, self powered

NB: According to a GnuRadio Wiki article, the Intel 82801DB device is 
acclaimed to be the best performer!

Reported configuration interrogated from userland

usbdevs -v
Controller /dev/usb3:
addr 1: high speed, self powered, config 1, EHCI root hub(0x0000), 
Intel(0x8086), rev 1.00
 port 1 addr 2: high speed, self powered, config 1, USRP Rev 2(0x0002), Free 
Software Folks(0xfffe), rev 1.02
 port 2 powered
 port 3 powered
 port 4 powered
 port 5 powered
 port 6 powered

I was led to believe that the FX2 interface is suppose to be configured as a 
fullspeed device. This doesn't appear to be the case as it is reports the 
configuration of a high speed device.

A evaluation of the USRP USB interface only managed to push 4MB/sec data 
bandwith which is below the expectation of a full speed USB device.

test_usrp_standard_{tx,rx}  utilities report underruns and overruns 
respectively until the decimation/interp value is adjusted to a value 
accommodating this speed.

Not being an expert in USB software development this leads me to my question:

What is required to get the show running at the next level of speed? In which 
aspects does the fusb_linux implementation differ from that of the generic 
version considering that both make use of the libusb library.

Currently, most example applications run with only a few overrun/underrun 
messages chiefly caused due to activities of other applications running on 
the same system, such as KMail checking for new mail etc., at the current 
4MB/sec limitation. "top" reports a CPU load of less than 10% for most 
GnuRadio example programs run on this system.

Any help, pointers and tips are very much welcomed and appreciated.

73, Berndt
Every man who says frankly and fully what he thinks is doing a public service.
[Leslie Stephen]

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