diff options
Diffstat (limited to 'decoders')
| -rw-r--r-- | decoders/usb/__init__.py | 32 | ||||
| -rw-r--r-- | decoders/usb/usb.py | 43 |
2 files changed, 55 insertions, 20 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 diff --git a/decoders/usb/usb.py b/decoders/usb/usb.py index 15b42a9..641ffe0 100644 --- a/decoders/usb/usb.py +++ b/decoders/usb/usb.py @@ -18,20 +18,21 @@ ## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA ## -# USB (full-speed) protocol decoder +# USB (low-speed and full-speed) protocol decoder import sigrokdecode as srd -# Symbols (used as states of our state machine, too) +# Full-speed symbols (used as states of our state machine, too). +# Note: Low-speed J and K are inverted compared to the full-speed J and K! syms = { - # (<dp>, <dm>): <state> + # (<dp>, <dm>): <symbol/state> (0, 0): 'SE0', (1, 0): 'J', (0, 1): 'K', (1, 1): 'SE1', } -# ... +# Packet IDs pids = { '10000111': 'OUT', # Tokens '10010110': 'IN', @@ -45,6 +46,19 @@ pids = { '01101001': 'NYET', } +def get_sym(signalling, dp, dm): + # Note: Low-speed J and K are inverted compared to the full-speed J and K! + if signalling == 'low-speed': + s = syms[dp, dm] + if s == 'J': + return 'K' + elif s == 'K': + return 'J' + else: + return s + elif signalling == 'full-speed': + return syms[dp, dm] + def bitstr_to_num(bitstr): if not bitstr: return 0 @@ -76,6 +90,7 @@ def packet_decode(packet): else: data = packet[16:] + # The SYNC pattern for low-speed/full-speed is KJKJKJKK (0001). if sync != '00000001': return 'SYNC INVALID!' @@ -85,8 +100,8 @@ class Decoder(srd.Decoder): api_version = 1 id = 'usb' name = 'USB' - longname = 'Universal Serial Bus' - desc = 'USB 1.x (full-speed) serial protocol.' + longname = 'Universal Serial Bus (LS/FS)' + desc = 'USB 1.x (low-speed and full-speed) serial protocol.' license = 'gplv2+' inputs = ['logic'] outputs = ['usb'] @@ -95,7 +110,9 @@ class Decoder(srd.Decoder): {'id': 'dm', 'name': 'D-', 'desc': 'USB D- signal'}, ] optional_probes = [] - options = {} + options = { + 'signalling': ['Signalling', 'full-speed'], + } annotations = [ ['Text', 'Human-readable text'] ] @@ -109,10 +126,6 @@ class Decoder(srd.Decoder): def start(self, metadata): self.samplerate = metadata['samplerate'] - if self.samplerate < 48000000: - raise Exception('Samplerate (%d) not sufficient for USB ' - 'decoding, need at least 48MHz' % self.samplerate) - # self.out_proto = self.add(srd.OUTPUT_PROTO, 'usb') self.out_ann = self.add(srd.OUTPUT_ANN, 'usb') @@ -127,7 +140,7 @@ class Decoder(srd.Decoder): # last change in the D+/D- lines. self.scount += 1 - sym = syms[dp, dm] + sym = get_sym(self.options['signalling'], dp, dm) # Wait for a symbol change (i.e., change in D+/D- lines). if sym == self.sym: @@ -142,7 +155,11 @@ class Decoder(srd.Decoder): # How many bits since the last transition? if self.packet != '' or self.sym != 'J': - bitcount = int((self.scount - 1) * 12000000 / self.samplerate) + if self.options['signalling'] == 'low-speed': + bitrate = 1500000 # 1.5Mb/s (+/- 1.5%) + elif self.options['signalling'] == 'full-speed': + bitrate = 12000000 # 12Mb/s (+/- 0.25%) + bitcount = int((self.scount - 1) * bitrate / self.samplerate) else: bitcount = 0 |