## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
##
-#
-# USB Full-speed protocol decoder
-#
-# Full-speed 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.
-# A state SE0 is defined where DP=DM=0. This common mode signal is used to
-# signal a reset or end of packet.
-#
-# 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.
-#
-# Details:
-# https://en.wikipedia.org/wiki/USB
-# http://www.usb.org/developers/docs/
-#
+# USB (full-speed) protocol decoder
import sigrokdecode as srd
-# States
-SE0, J, K, SE1 = 0, 1, 2, 3
-
-# ...
+# Symbols (used as states of our state machine, too)
syms = {
- (0, 0): SE0,
- (1, 0): J,
- (0, 1): K,
- (1, 1): SE1,
+ (0, 0): 'SE0',
+ (1, 0): 'J',
+ (0, 1): 'K',
+ (1, 1): 'SE1',
}
# ...
{'id': 'dp', 'name': 'D+', 'desc': 'USB D+ signal'},
{'id': 'dm', 'name': 'D-', 'desc': 'USB D- signal'},
]
- extra_probes = []
+ optional_probes = []
options = {}
annotations = [
['TODO', 'TODO']
'decoding, need at least 48MHz' % self.rate)
# Initialise decoder state.
- self.sym = J
+ self.sym = 'J'
self.scount = 0
self.packet = ''
continue
# How many bits since the last transition?
- if self.packet != '' or self.sym != J:
+ if self.packet != '' or self.sym != 'J':
bitcount = int((self.scount - 1) * 12000000 / self.rate)
else:
bitcount = 0
- if self.sym == SE0:
+ if self.sym == 'SE0':
if bitcount == 1:
# End-Of-Packet (EOP)
self.put(0, 0, self.out_ann,
self.packet += '1' * bitcount
# Handle bit stuffing.
- if bitcount < 6 and sym != SE0:
+ if bitcount < 6 and sym != 'SE0':
self.packet += '0'
elif bitcount > 6:
self.put(0, 0, self.out_ann, [0, ['BIT STUFF ERROR']])