Format of the mode-switch message
Posted: 07 Dec 2007, 16:21
Hello
Here's some info on the switch message sent over the BULK OUT endpoint of an Option Icon. This info may be true for other devices.
The format of the switch message is in fact a CBW structure as defined in the USB Mass Storage device class specification. It always is 31 bytes in length and formatted like this:
+00h: 55 53 42 43 : CBW signature
+04h: 70 6e de 86 : Tag; value is not important
+08h: 00 00 00 00 : Data transfer length
+0Ch: 00 : Flags
+0Dh: 00 : Bit 0..3 : Logical Unit Number; bit 4..7 : Reserved
+0Eh: 06 : Length of the SCSI command
+0Fh: 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 : SCSI command
The CBW sends a REZERO UNIT SCSI command to the mass storage device. This is a 6-byte command: 01h 00h 00h 00h 00h 00h.
The device will not return a CSW over the BULK IN endpoint. It simply disconnects, and then reconnects with the USB IDs for 3G modem.
Here's some info on the switch message sent over the BULK OUT endpoint of an Option Icon. This info may be true for other devices.
The format of the switch message is in fact a CBW structure as defined in the USB Mass Storage device class specification. It always is 31 bytes in length and formatted like this:
+00h: 55 53 42 43 : CBW signature
+04h: 70 6e de 86 : Tag; value is not important
+08h: 00 00 00 00 : Data transfer length
+0Ch: 00 : Flags
+0Dh: 00 : Bit 0..3 : Logical Unit Number; bit 4..7 : Reserved
+0Eh: 06 : Length of the SCSI command
+0Fh: 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 : SCSI command
The CBW sends a REZERO UNIT SCSI command to the mass storage device. This is a 6-byte command: 01h 00h 00h 00h 00h 00h.
The device will not return a CSW over the BULK IN endpoint. It simply disconnects, and then reconnects with the USB IDs for 3G modem.