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

[Berndt Josef Wulf]

G'day,

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
VK5ABN
-- 
Every man who says frankly and fully what he thinks is doing a public service.
[Leslie Stephen]