Bus snooping/sniffing

Purpose and relevance to development work -- description coming soon

PCI / PCIe

Snooping Utilities:

• BTSpy [1] - Windows based snoop for BT8x8 based devices
• Dscaler's RegSpy [2] - Windows based; contains the ability to snoop the registers of PCI / PCIe interface chipsets ... also see this note

USB

Snooping Utilities:

• usbsnoop - a Windows based utility for sniffing/monitoring communications traffic for a USB device. Note: In case usbsnoop/SniffUSB doesn't work for you, here are a few time limited apps that should work under Vista:
  • USB Monitor - 14-day trial period
  • USBlyzer - fully functional evaluation version for 33 days
• SnoopyPro - Windows based snoop for USB device communications traffic
• usbsnoop/SniffUSB - Windows based snoop for USB device communications traffic
• usbmon - Linux kernel module which can snoop USB device communications traffic
  • Wireshark - logs usbmon output, via libpcap
  • USBMon - logs usbmon output

Log parsers, format etc

• [parser.pl]
• usbmon2usbsnoop
• [em28xx log parser]

...

Snooping Procedures:

• Use a Snopping utility to get the log.
• Group URB transactions into a shorter log by using a parser
• Identify the URB transactions at the control endpoint. URB transactions look like those:

40 02 00 00 ba 00 03 00 >>> 20 11 00

URB fields

Byte	Meaning
1	bit 7 = 1 - IN / 0 - OUT bit 6 = 1 - Vendor Class
2	URB Request
3-4	URB Value in big endian
5-6	URB Index in big endian
7-8	URB message size in big endian

For example, let's analyse the folowing URB's:

control URB examples

40 00 00 00 08 00 01 00 >>> 3d	USB OUT, Vendor class, Req = 0, Value = 0x0000, Index = 0x0008, Size = 0x0001, Message = 0x3d
40 02 00 00 ba 00 03 00 >>> 20 11 00	USB OUT, Vendor class, Req = 0x02, Value = 0x0000, Index = 0x00ba, Size = 0x0003, Message = "0x20, 0x11, 0x00"
c0 00 00 00 15 00 01 00 <<< 00	USB IN, Vendor class, Req = 0x00, Value = 0x0000, Index = 0x0015, Size = 0x0001, Message = "0x00"

After getting the log, you should analyse and understand the meaning of each of URB fields on your device.

For example, in the case of em28xx, Req is used to indicate internal registers or I2C, Value is always 0 and Index indicates what device register is being used.

On em28xx, the [em28xx log parser] could be used in order to proccess the URBs and the driver dmesg dumps (in the compact format as shown above) and print them into a more human way, generating C like statements that can be added at em28xx source code (with a few adaptations, in the case of i2c messages):

 em28xx_write_reg(dev, EM28XX_R08_GPIO, 0x3d);
 i2c_master_send(0xba>>1, { 20 11 00  }, 0x03);
 em28xx_read_reg(dev, EM28XX_R15_RGAIN);         /* read 0x00 */

Command Playback Utilities:

• usb-robot - plays back USB Snoopy capture logs
• usbreplay - plays back usbsnoop capture logs

i2c

• i2c Tools: see here and here
• http://en.wikipedia.org/wiki/I2C#Development_Tools
• also see this thread

External Links

• Wikipedia's Bus sniffing article; note that the Cache coherency article is a probably a little less vague or more enlightening