ieee488: introduce 'delim' option for improved text output

When a capture contains output from a talking device, but neither
contains EOI (end of transmission) nor ATN (new commands, including
changes in the set of communicating peers or communication direction),
then lower layer data bytes would be shown but accumulated runs of upper
layer payload data would not. The hp53131a-ton.sr capture demonstrates
this behaviour.

Add transparent support for the typical case of communicating SCPI over
GPIB. Do emit upper layer payload data annotations when termination
sequences for text lines were seen. Allow users to disable this feature
when it's not appropriate for binary content.

It's an internal implementation detail that accumulated data gets flushed.
Communicate the user visible option as "payload data separation", which
should most appropriately reflect the resulting behaviour. The specific
implementation of this feature can also support different kinds of payload
chunk separation.

1 files changed, 29 insertions, 0 deletions

diff --git a/decoders/ieee488/pd.py b/decoders/ieee488/pd.py
index b4efac0..e0c2ef6 100644
--- a/decoders/ieee488/pd.py
+++ b/decoders/ieee488/pd.py
@@ -286,6 +286,8 @@ class Decoder(srd.Decoder):
     options = (
         {'id': 'iec_periph', 'desc': 'Decode Commodore IEC bus peripherals details',
             'default': 'no', 'values': ('no', 'yes')},
+        {'id': 'delim', 'desc': 'Payload data delimiter',
+            'default': 'eol', 'values': ('none', 'eol')},
     )
     annotations = (
         ('bit', 'IEC bit'),
@@ -374,6 +376,31 @@ class Decoder(srd.Decoder):
             self.accu_text = []
         self.ss_text = self.es_text = None
 
+    def check_extra_flush(self, b):
+        # Optionally flush previously accumulated runs of payload data
+        # according to user specified conditions.
+        if self.options['delim'] == 'none':
+            return
+        if not self.accu_bytes:
+            return
+
+        # This implementation exlusively handles "text lines", but adding
+        # support for more variants here is straight forward.
+        #
+        # Search for the first data byte _after_ a user specified text
+        # line termination sequence was seen. The termination sequence's
+        # alphabet may be variable, and the sequence may span multiple
+        # data bytes. We accept either CR or LF, and combine the CR+LF
+        # sequence to strive for maximum length annotations for improved
+        # readability at different zoom levels. It's acceptable that this
+        # implementation would also combine multiple line terminations
+        # like LF+LF.
+        term_chars = (10, 13)
+        is_eol = b in term_chars
+        had_eol = self.accu_bytes[-1] in term_chars
+        if had_eol and not is_eol:
+            self.flush_bytes_text_accu()
+
     def handle_ifc_change(self, ifc):
         # Track IFC line for parallel input.
         # Assertion of IFC de-selects all talkers and listeners.
@@ -446,6 +473,8 @@ class Decoder(srd.Decoder):
             # TODO Process data depending on peripheral type and channel?
 
     def handle_data_byte(self):
+        if not self.curr_atn:
+            self.check_extra_flush(self.curr_raw)
         b = self.curr_raw
         texts = _get_raw_text(b, self.curr_atn)
         self.emit_data_ann(self.ss_raw, self.es_raw, ANN_RAW_BYTE, texts)