diff options
Diffstat (limited to 'decoders/usb/__init__.py')
| -rw-r--r-- | decoders/usb/__init__.py | 32 |
1 files changed, 25 insertions, 7 deletions
diff --git a/decoders/usb/__init__.py b/decoders/usb/__init__.py index a7204db..1a16f8f 100644 --- a/decoders/usb/__init__.py +++ b/decoders/usb/__init__.py @@ -19,21 +19,39 @@ ## ''' -USB (full-speed) protocol decoder. +USB (low-speed and full-speed) protocol decoder. -Full-speed USB signalling consists of two signal lines, both driven at 3.3V +USB signalling consists of two signal lines, both driven at 3.3V logic levels. The signals are DP (D+) and DM (D-), and normally operate in differential mode. -The state where DP=1,DM=0 is J, the state DP=0,DM=1 is K. + +Low-speed: The state where DP=1,DM=0 is K, the state DP=0,DM=1 is J. +Full-speed: The state where DP=1,DM=0 is J, the state DP=0,DM=1 is K. + A state SE0 is defined where DP=DM=0. This common mode signal is used to -signal a reset or end of packet. +signal a reset or end of packet. A state SE1 is defined where DP=DM=1. Data transmitted on the USB is encoded with NRZI. A transition from J to K or vice-versa indicates a logic 0, while no transition indicates a logic 1. If 6 ones are transmitted consecutively, a zero is inserted to force a -transition. This is known as bit stuffing. Data is transferred at a rate -of 12Mbit/s. The SE0 transmitted to signal an end-of-packet is two bit -intervals long. +transition. This is known as bit stuffing. + +Data is transferred at a rate of 1.5Mbit/s (low-speed) / 12Mbit/s (full-speed). + +The SE0 transmitted to signal an end-of-packet is two bit intervals long +(low-speed: 1.25uS - 1.50uS, full-speed: 160ns - 175ns). + +Bit/byte ordering: Bits are sent onto the bus LSB-first. Multibyte fields +are transmitted in little-endian order (i.e., LSB to MSB). + +SYNC field: All packets begin with a SYNC field (8 bits). + +Packet field format: Packets start with an SOP (Start Of Packet) delimiter +that is part of the SYNC field, and end with an EOP (End Of Packet). + +PID: A PID (packet identifier) follows the SYNC field of every packet. A PID +consists of a 4-bit packet type field, and a 4 bit check field. +The check field is the one's complement of the packet type field. Protocol output format: TODO |