From d4364948d0356f0659e1777cf771ed5bfc1f2072 Mon Sep 17 00:00:00 2001 From: Andrew Gregory Date: Wed, 5 Dec 2018 23:31:34 +0800 Subject: modbus: Make C->S and S->C configurable, add framegap option. Change client->server and server->client to be separately configurable, allowing decoding at both the server (where client->server is RX and server->client is TX) and client (where client->server is TX and server->client is RX) ends of the link. It also allows monitoring of the bus on a single channel (where client->server and server->client are both RX (or TX)). When I tried to decode a bus capture, I found that when the transmitter was turned off it generated a false start bit, which in turn resulted in a false trailing byte from the UART decoder. This narrowed the inter-frame gap to the point where the Modbus decoder failed to recognise a new frame. The result was only the first frame of the capture decoded - all the rest of the frames failed to decode. I had to reduce the frame gap to allow subsequent frames to decode, and so made it a configurable option that defaults to the existing gap. Lastly, I fixed a call to puti() that incorrectly included the annotation prefix. --- decoders/modbus/pd.py | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-) (limited to 'decoders/modbus') diff --git a/decoders/modbus/pd.py b/decoders/modbus/pd.py index d5b39ca..d5cb811 100644 --- a/decoders/modbus/pd.py +++ b/decoders/modbus/pd.py @@ -22,6 +22,7 @@ from math import ceil RX = 0 TX = 1 +rxtx_channels = ('RX', 'TX') class No_more_data(Exception): '''This exception is a signal that we should stop parsing an ADU as there @@ -124,18 +125,18 @@ class Modbus_ADU: self.annotation_prefix + 'error', 'Message too short or not finished') self.hasError = True - if self.hasError and self.parent.options['channel'] == 'RX': - # If we are on RX mode (so client->server and server->client - # messages can be seperated) we like to mark blocks containing - # errors. We don't do this in TX mode, because then we interpret - # each frame as both a client->server and server->client frame, and + if self.hasError and self.parent.options['scchannel'] != self.parent.options['cschannel']: + # If we are decoding different channels (so client->server and + # server->client messages can be separated) we like to mark blocks + # containing errors. We don't do this when decoding the same + # channel as both a client->server and server->client frame, and # one of those is bound to contain an error, making highlighting # frames useless. self.parent.puta(data[0].start, data[-1].end, 'error-indication', 'Frame contains error') if len(data) > 256: try: - self.puti(len(data) - 1, self.annotation_prefix + 'error', + self.puti(len(data) - 1, 'error', 'Modbus data frames are limited to 256 bytes') except No_more_data: pass @@ -843,8 +844,11 @@ class Decoder(srd.Decoder): ('error-indicator', 'Errors in frame', (14,)), ) options = ( - {'id': 'channel', 'desc': 'Server -> client channel', 'default': 'RX', - 'values': ('RX', 'TX')}, + {'id': 'scchannel', 'desc': 'Server -> client channel', + 'default': rxtx_channels[0], 'values': rxtx_channels}, + {'id': 'cschannel', 'desc': 'Client -> server channel', + 'default': rxtx_channels[1], 'values': rxtx_channels}, + {'id': 'framegap', 'desc': 'Inter-frame bit gap', 'default': '28'}, ) def __init__(self): @@ -908,7 +912,7 @@ class Decoder(srd.Decoder): # somewhere between seems fine. # A character is 11 bits long, so (3.5 + 1.5)/2 * 11 ~= 28 # TODO: Display error for too short or too long. - if (ss - ADU.last_read) <= self.bitlength * 28: + if (ss - ADU.last_read) <= self.bitlength * int(self.options['framegap']): ADU.add_data(ss, es, data) else: # It's been too long since the last part of the ADU! @@ -927,9 +931,7 @@ class Decoder(srd.Decoder): # Decide what ADU(s) we need this packet to go to. # Note that it's possible to go to both ADUs. - if rxtx == TX: - self.decode_adu(ss, es, data, 'Cs') - if rxtx == TX and self.options['channel'] == 'TX': - self.decode_adu(ss, es, data, 'Sc') - if rxtx == RX and self.options['channel'] == 'RX': + if rxtx_channels[rxtx] == self.options['scchannel']: self.decode_adu(ss, es, data, 'Sc') + if rxtx_channels[rxtx] == self.options['cschannel']: + self.decode_adu(ss, es, data, 'Cs') -- cgit v1.2.3-70-g09d2