diff options
Diffstat (limited to 'decoders')
| -rw-r--r-- | decoders/usb/__init__.py | 4 | ||||
| -rw-r--r-- | decoders/usb/usb.py | 44 |
2 files changed, 36 insertions, 12 deletions
diff --git a/decoders/usb/__init__.py b/decoders/usb/__init__.py index 1a16f8f..313c495 100644 --- a/decoders/usb/__init__.py +++ b/decoders/usb/__init__.py @@ -21,6 +21,8 @@ ''' USB (low-speed and full-speed) protocol decoder. +Electrical/signalling layer (USB spec, chapter 7): + 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. @@ -41,6 +43,8 @@ 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). +Protocol layer (USB spec, chapter 8): + Bit/byte ordering: Bits are sent onto the bus LSB-first. Multibyte fields are transmitted in little-endian order (i.e., LSB to MSB). diff --git a/decoders/usb/usb.py b/decoders/usb/usb.py index 641ffe0..529868e 100644 --- a/decoders/usb/usb.py +++ b/decoders/usb/usb.py @@ -32,18 +32,38 @@ syms = { (1, 1): 'SE1', } -# Packet IDs +# Packet IDs (PIDs). +# The first 4 bits are the 'packet type' field, the last 4 bits are the +# 'check field' (each bit in the check field must be the inverse of the resp. +# bit in the 'packet type' field; if not, that's a 'PID error'). +# For the 4-bit strings, the left-most '1' or '0' is the LSB, i.e. it's sent +# to the bus first. pids = { - '10000111': 'OUT', # Tokens - '10010110': 'IN', - '10100101': 'SOF', - '10110100': 'SETUP', - '11000011': 'DATA0', # Data - '11010010': 'DATA1', - '01001011': 'ACK', # Handshake - '01011010': 'NAK', - '01111000': 'STALL', - '01101001': 'NYET', + # Tokens + '10000111': ['OUT', 'Address & EP number in host-to-function transaction'], + '10010110': ['IN', 'Address & EP number in function-to-host transaction'], + '10100101': ['SOF', 'Start-Of-Frame marker & frame number'], + '10110100': ['SETUP', 'Address & EP number in host-to-function transaction for SETUP to a control pipe'], + + # Data + # Note: DATA2 and MDATA are HS-only. + '11000011': ['DATA0', 'Data packet PID even'], + '11010010': ['DATA1', 'Data packet PID odd'], + '11100001': ['DATA2', 'Data packet PID HS, high bandwidth isosynchronous transaction in a microframe'], + '11110000': ['MDATA', 'Data packet PID HS for split and high-bandwidth isosynchronous transactions'], + + # Handshake + '01001011': ['ACK', 'Receiver accepts error-free packet'], + '01011010': ['NAK', 'Receiver cannot accept or transmitter cannot send'], + '01111000': ['STALL', 'EP halted or control pipe request unsupported'], + '01101001': ['NYET', 'No response yet from receiver'], + + # Special + '00111100': ['PRE', 'Host-issued preamble; enables downstream bus traffic to low-speed devices'], + '00111100': ['ERR', 'Split transaction error handshake'], + '00011110': ['SPLIT', 'HS split transaction token'], + '00101101': ['PING', 'HS flow control probe for a bulk/control EP'], + '00001111': ['Reserved', 'Reserved PID'], } def get_sym(signalling, dp, dm): @@ -69,7 +89,7 @@ def bitstr_to_num(bitstr): def packet_decode(packet): sync = packet[:8] pid = packet[8:16] - pid = pids.get(pid, pid) + pid = pids.get(pid, (pid, ''))[0] # Remove CRC. if pid in ('OUT', 'IN', 'SOF', 'SETUP'): |