2 ## This file is part of the sigrok project.
4 ## Copyright (C) 2011 Uwe Hermann <uwe@hermann-uwe.de>
6 ## This program is free software; you can redistribute it and/or modify
7 ## it under the terms of the GNU General Public License as published by
8 ## the Free Software Foundation; either version 2 of the License, or
9 ## (at your option) any later version.
11 ## This program is distributed in the hope that it will be useful,
12 ## but WITHOUT ANY WARRANTY; without even the implied warranty of
13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 ## GNU General Public License for more details.
16 ## You should have received a copy of the GNU General Public License
17 ## along with this program; if not, write to the Free Software
18 ## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
22 # UART protocol decoder
26 # Universal Asynchronous Receiver Transmitter (UART) is a simple serial
27 # communication protocol which allows two devices to talk to each other.
29 # It uses just two data signals and a ground (GND) signal:
30 # - RX/RXD: Receive signal
31 # - TX/TXD: Transmit signal
33 # The protocol is asynchronous, i.e., there is no dedicated clock signal.
34 # Rather, both devices have to agree on a baudrate (number of bits to be
35 # transmitted per second) beforehand. Baudrates can be arbitrary in theory,
36 # but usually the choice is limited by the hardware UARTs that are used.
37 # Common values are 9600 or 115200.
39 # The protocol allows full-duplex transmission, i.e. both devices can send
40 # data at the same time. However, unlike SPI (which is always full-duplex,
41 # i.e., each send operation is automatically also a receive operation), UART
42 # allows one-way communication, too. In such a case only one signal (and GND)
45 # The data is sent over the TX line in so-called 'frames', which consist of:
46 # - Exactly one start bit (always 0/low).
47 # - Between 5 and 9 data bits.
48 # - An (optional) parity bit.
49 # - One or more stop bit(s).
51 # The idle state of the RX/TX line is 1/high. As the start bit is 0/low, the
52 # receiver can continually monitor its RX line for a falling edge, in order
53 # to detect the start bit.
55 # Once detected, it can (due to the agreed-upon baudrate and thus the known
56 # width/duration of one UART bit) sample the state of the RX line "in the
57 # middle" of each (start/data/parity/stop) bit it wants to analyze.
59 # It is configurable whether there is a parity bit in a frame, and if yes,
60 # which type of parity is used:
61 # - None: No parity bit is included.
62 # - Odd: The number of 1 bits in the data (and parity bit itself) is odd.
63 # - Even: The number of 1 bits in the data (and parity bit itself) is even.
64 # - Mark/one: The parity bit is always 1/high (also called 'mark state').
65 # - Space/zero: The parity bit is always 0/low (also called 'space state').
67 # It is also configurable how many stop bits are to be used:
68 # - 1 stop bit (most common case)
70 # - 1.5 stop bits (i.e., one stop bit, but 1.5 times the UART bit width)
71 # - 0.5 stop bits (i.e., one stop bit, but 0.5 times the UART bit width)
73 # The bit order of the 5-9 data bits is LSB-first.
75 # Possible special cases:
76 # - One or both data lines could be inverted, which also means that the idle
77 # state of the signal line(s) is low instead of high.
78 # - Only the data bits on one or both data lines (and the parity bit) could
79 # be inverted (but the start/stop bits remain non-inverted).
80 # - The bit order could be MSB-first instead of LSB-first.
81 # - The baudrate could change in the middle of the communication. This only
82 # happens in very special cases, and can only work if both devices know
83 # to which baudrate they are to switch, and when.
84 # - Theoretically, the baudrate on RX and the one on TX could also be
85 # different, but that's a very obscure case and probably doesn't happen
86 # very often in practice.
89 # - If there is a parity bit, but it doesn't match the expected parity,
90 # this is called a 'parity error'.
91 # - If there are no stop bit(s), that's called a 'frame error'.
100 WAIT_FOR_START_BIT = 0
123 # Output data formats
124 DATA_FORMAT_ASCII = 0
127 # TODO: Remove me later.
131 def __init__(self, data):
133 def probe(self, probe):
134 s = ord(self.data[probe / 8]) & (1 << (probe % 8))
135 return True if s else False
137 def sampleiter(data, unitsize):
138 for i in range(0, len(data), unitsize):
139 yield(Sample(data[i:i+unitsize]))
141 # Given a parity type to check (odd, even, zero, one), the value of the
142 # parity bit, the value of the data, and the length of the data (5-9 bits,
143 # usually 8 bits) return True if the parity is correct, False otherwise.
144 # PARITY_NONE is _not_ allowed as value for 'parity_type'.
145 def parity_ok(parity_type, parity_bit, data, num_data_bits):
147 # Handle easy cases first (parity bit is always 1 or 0).
148 if parity_type == PARITY_ZERO:
149 return parity_bit == 0
150 elif parity_type == PARITY_ONE:
151 return parity_bit == 1
153 # Count number of 1 (high) bits in the data (and the parity bit itself!).
154 parity = bin(data).count('1') + parity_bit
156 # Check for odd/even parity.
157 if parity_type == PARITY_ODD:
158 return (parity % 2) == 1
159 elif parity_type == PARITY_EVEN:
160 return (parity % 2) == 0
162 raise Exception('Invalid parity type: %d' % parity_type)
164 class Decoder(sigrok.Decoder):
167 longname = 'Universal Asynchronous Receiver/Transmitter (UART)'
168 desc = 'Universal Asynchronous Receiver/Transmitter (UART)'
170 author = 'Uwe Hermann'
171 email = 'uwe@hermann-uwe.de'
176 # Allow specifying only one of the signals, e.g. if only one data
177 # direction exists (or is relevant).
178 ## 'rx': {'ch': 0, 'name': 'RX', 'desc': 'UART receive line'},
179 ## 'tx': {'ch': 1, 'name': 'TX', 'desc': 'UART transmit line'},
184 'baudrate': ['UART baud rate', 115200],
185 'num_data_bits': ['Data bits', 8], # Valid: 5-9.
186 'parity': ['Parity', PARITY_NONE],
187 'parity_check': ['Check parity', True],
188 'num_stop_bits': ['Stop bit(s)', STOP_BITS_1],
189 'bit_order': ['Bit order', LSB_FIRST],
190 'data_format': ['Output data format', DATA_FORMAT_ASCII],
191 # TODO: Options to invert the signal(s).
195 def __init__(self, **kwargs):
196 self.probes = Decoder.probes.copy()
198 # Set defaults, can be overridden in 'start'.
199 self.baudrate = 115200
200 self.num_data_bits = 8
201 self.parity = PARITY_NONE
202 self.check_parity = True
203 self.num_stop_bits = 1
204 self.bit_order = LSB_FIRST
205 self.data_format = DATA_FORMAT_ASCII
208 self.frame_start = -1
210 self.cur_data_bit = 0
213 self.startsample = -1
216 self.staterx = WAIT_FOR_START_BIT
218 # Get the channel/probe number of the RX/TX signals.
219 ## self.rx_bit = self.probes['rx']['ch']
220 ## self.tx_bit = self.probes['tx']['ch']
221 self.rx_bit = self.probes['rx']
222 self.tx_bit = self.probes['tx']
227 def start(self, metadata):
228 self.unitsize = metadata['unitsize']
229 self.samplerate = metadata['samplerate']
232 ### self.baudrate = metadata['baudrate']
233 ### self.num_data_bits = metadata['num_data_bits']
234 ### self.parity = metadata['parity']
235 ### self.parity_check = metadata['parity_check']
236 ### self.num_stop_bits = metadata['num_stop_bits']
237 ### self.bit_order = metadata['bit_order']
238 ### self.data_format = metadata['data_format']
240 # The width of one UART bit in number of samples.
241 self.bit_width = float(self.samplerate) / float(self.baudrate)
246 # Return true if we reached the middle of the desired bit, false otherwise.
247 def reached_bit(self, bitnum):
248 # bitpos is the samplenumber which is in the middle of the
249 # specified UART bit (0 = start bit, 1..x = data, x+1 = parity bit
250 # (if used) or the first stop bit, and so on).
251 bitpos = self.frame_start + (self.bit_width / 2.0)
252 bitpos += bitnum * self.bit_width
253 if self.samplenum >= bitpos:
257 def reached_bit_last(self, bitnum):
258 bitpos = self.frame_start + ((bitnum + 1) * self.bit_width)
259 if self.samplenum >= bitpos:
263 def wait_for_start_bit(self, old_signal, signal):
264 # The start bit is always 0 (low). As the idle UART (and the stop bit)
265 # level is 1 (high), the beginning of a start bit is a falling edge.
266 if not (old_signal == 1 and signal == 0):
269 # Save the sample number where the start bit begins.
270 self.frame_start = self.samplenum
272 self.staterx = GET_START_BIT
274 def get_start_bit(self, signal):
275 # Skip samples until we're in the middle of the start bit.
276 if not self.reached_bit(0):
279 self.startbit = signal
281 if self.startbit != 0:
282 # TODO: Startbit must be 0. If not, we report an error.
285 self.cur_data_bit = 0
287 self.startsample = -1
289 self.staterx = GET_DATA_BITS
291 if quick_hack: # TODO
294 o = [{'type': 'S', 'range': (self.frame_start, self.samplenum),
295 'data': None, 'ann': 'Start bit'}]
298 def get_data_bits(self, signal):
299 # Skip samples until we're in the middle of the desired data bit.
300 if not self.reached_bit(self.cur_data_bit + 1):
303 # Save the sample number where the data byte starts.
304 if self.startsample == -1:
305 self.startsample = self.samplenum
307 # Get the next data bit in LSB-first or MSB-first fashion.
308 if self.bit_order == LSB_FIRST:
310 self.databyte |= (signal << (self.num_data_bits - 1))
311 elif self.bit_order == MSB_FIRST:
313 self.databyte |= (signal << 0)
315 raise Exception('Invalid bit order value: %d', self.bit_order)
317 # Return here, unless we already received all data bits.
318 if self.cur_data_bit < self.num_data_bits - 1: # TODO? Off-by-one?
319 self.cur_data_bit += 1
322 # Convert the data byte into the configured format.
323 if self.data_format == DATA_FORMAT_ASCII:
324 d = chr(self.databyte)
325 elif self.data_format == DATA_FORMAT_HEX:
326 d = '0x%02x' % self.databyte
328 raise Exception('Invalid data format value: %d', self.data_format)
330 self.staterx = GET_PARITY_BIT
332 if quick_hack: # TODO
335 o = [{'type': 'D', 'range': (self.startsample, self.samplenum - 1),
336 'data': d, 'ann': None}]
340 def get_parity_bit(self, signal):
341 # If no parity is used/configured, skip to the next state immediately.
342 if self.parity == PARITY_NONE:
343 self.staterx = GET_STOP_BITS
346 # Skip samples until we're in the middle of the parity bit.
347 if not self.reached_bit(self.num_data_bits + 1):
350 self.paritybit = signal
352 self.staterx = GET_STOP_BITS
354 if parity_ok(self.parity, self.paritybit, self.databyte,
356 if quick_hack: # TODO
360 o = [{'type': 'P', 'range': (self.samplenum, self.samplenum),
361 'data': self.paritybit, 'ann': 'Parity bit'}]
363 if quick_hack: # TODO
365 o = [{'type': 'PE', 'range': (self.samplenum, self.samplenum),
366 'data': self.paritybit, 'ann': 'Parity error'}]
370 # TODO: Currently only supports 1 stop bit.
371 def get_stop_bits(self, signal):
372 # Skip samples until we're in the middle of the stop bit(s).
374 if self.parity != PARITY_NONE:
376 if not self.reached_bit(self.num_data_bits + 1 + skip_parity):
379 self.stopbit1 = signal
381 if self.stopbit1 != 1:
382 # TODO: Stop bits must be 1. If not, we report an error.
385 self.staterx = WAIT_FOR_START_BIT
387 if quick_hack: # TODO
391 o = [{'type': 'P', 'range': (self.samplenum, self.samplenum),
392 'data': None, 'ann': 'Stop bit'}]
395 def decode(self, data):
396 """UART protocol decoder"""
400 for sample in sampleiter(data["data"], self.unitsize):
402 # TODO: Eliminate the need for ord().
405 # TODO: Start counting at 0 or 1? Increase before or after?
408 # First sample: Save RX/TX value.
409 if self.oldrx == None:
410 # Get RX/TX bit values (0/1 for low/high) of the first sample.
411 self.oldrx = (s & (1 << self.rx_bit)) >> self.rx_bit
412 # self.oldtx = (s & (1 << self.tx_bit)) >> self.tx_bit
415 # Get RX/TX bit values (0/1 for low/high).
416 rx = (s & (1 << self.rx_bit)) >> self.rx_bit
417 # tx = (s & (1 << self.tx_bit)) >> self.tx_bit
420 if self.staterx == WAIT_FOR_START_BIT:
421 self.wait_for_start_bit(self.oldrx, rx)
422 elif self.staterx == GET_START_BIT:
423 out += self.get_start_bit(rx)
424 elif self.staterx == GET_DATA_BITS:
425 out += self.get_data_bits(rx)
426 elif self.staterx == GET_PARITY_BIT:
427 out += self.get_parity_bit(rx)
428 elif self.staterx == GET_STOP_BITS:
429 out += self.get_stop_bits(rx)
431 raise Exception('Invalid state: %s' % self.staterx)
433 # Save current RX/TX values for the next round.