The usbmon's documentation leaves me dissatisfied, it seems clumsy.
What do you native English speaker guys think about the below, is
it any improvement?
--- linux-2.6.17-rc5/Documentation/usb/usbmon.txt 2005-09-13
01:05:37.000000000 -0700
+++ linux-2.6.17-rc5-lem/Documentation/usb/usbmon.txt 2006-06-09
21:23:00.000000000 -0700
@@ -99,18 +98,22 @@
Bi Bo Bulk input and output
Device address and Endpoint number are decimal numbers with leading zeroes
or 3 and 2 positions, correspondingly.
-- URB Status. This field makes no sense for submissions, but is present
- to help scripts with parsing. In error case, it contains the error code.
- In case of a setup packet, it contains a Setup Tag. If scripts read a number
- in this field, they proceed to read Data Length. Otherwise, they read
- the setup packet before reading the Data Length.
+- URB Status. In most cases, this field contains a number, sometimes negative,
+ which represents a "status" field of the URB. This field makes no sense for
+ submissions, but is present anyway to help scripts with parsing. In error
+ case, it contains the error code. In case of a submission of Control packet,
+ this field is overlaid with a Setup Tag. It is easy to tell, which field it
+ actually is. If scripts read a number in this field, they proceed to read
+ Data Length. If they get something else, like a letter, they read the setup
+ packet before reading the Data Length.
- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
packet was present, but not captured, and the fields contain filler.
-- Data Length. This is the actual length in the URB.
+- Data Length. For submissions, this is the requested length. For callbacks,
+ this is the actual length.
- Data tag. The usbmon may not always capture data, even if length is nonzero.
- Only if tag is '=', the data words are present.
+ Only if this tag is '=', the data words are present.
- Data words follow, in big endian hexadecimal format. Notice that they are
not machine words, but really just a byte stream split into words to make
it easier to read. Thus, the last word may contain from one to four bytes.
Thanks,
-- Pete
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