First attempt at an I2C decoder (untested).

diff --git a/decode.c b/decode.c
index de37913cddf9bd13d0f7be8e754b34bb473a5827..d4890682e681c9e2dc72ad547c1fa0f9247d2a03 100644 (file)
--- a/decode.c
+++ b/decode.c
@@ -35,9 +35,9 @@ int sigrokdecode_init(void)
        /* Allows for ./gui/sigrok-gui in the top-level directory. */
        PySys_SetPath("libsigrokdecode/scripts");
        /* Allows for ./sigrok-gui in the gui/ directory. */
-       PySys_SetPath("../libsigrokdecode/scripts");
+       // PySys_SetPath("../libsigrokdecode/scripts");
        /* Allows for sigrok-gui from anywhere given sigrok is installed. */
-       PySys_SetPath("/usr/local/share/sigrok");
+       // PySys_SetPath("/usr/local/share/sigrok");
 
        return 0;
 }
@@ -71,7 +71,8 @@ int sigrokdecode_run_decoder(const char *decodername, uint8_t *inbuf,
                             uint64_t inbuflen, uint8_t **outbuf,
                             uint64_t *outbuflen)
 {
-       const char *decoder_filename = "transitioncounter"; /* FIXME */
+       // const char *decoder_filename = "transitioncounter"; /* FIXME */
+       const char *decoder_filename = "i2c"; /* FIXME */
        PyObject *py_name, *py_module, *py_func, *py_args;
        PyObject *py_value, *py_result;
        int ret;

diff --git a/scripts/i2c.py b/scripts/i2c.py
new file mode 100644 (file)
index 0000000..f7022f5
--- /dev/null
+++ b/scripts/i2c.py
@@ -0,0 +1,164 @@
+##
+## This file is part of the sigrok project.
+##
+## Copyright (C) 2010 Uwe Hermann <uwe@hermann-uwe.de>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 2 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, write to the Free Software
+## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+##
+
+#
+# I2C protocol decoder
+#
+
+#
+# The Inter-Integrated Circuit (I2C) bus is a bidirectional, multi-master
+# bus using two signals (SCL = serial clock line, SDA = serial data line).
+#
+# There can be many devices on the same bus. Each device can potentially be
+# master or slave (and that can change during runtime). Both slave and master
+# can potentially play the transmitter or receiver role (this can also
+# change at runtime).
+#
+# Possible maximum data rates:
+#  - Standard mode: 100 kbit/s
+#  - Fast mode: 400 kbit/s
+#  - Fast-mode Plus: 1 Mbit/s
+#  - High-speed mode: 3.4 Mbit/s
+#
+# START condition (S): SDA = falling, SCL = high
+# Repeated START condition (Sr): same as S
+# STOP condition (P): SDA = rising, SCL = high
+#
+# All data bytes on SDA are extactly 8 bits long (transmitted MSB-first).
+# Each byte has to be followed by a 9th ACK/NACK bit. If that bit is low,
+# that indicates an ACK, if it's high that indicates a NACK.
+#
+# After the first START condition, a master sends the device address of the
+# slave it wants to talk to. Slave addresses are 7 bits long (MSB-first).
+# After those 7 bits a data direction bit is sent. If the bit is low that
+# indicates a WRITE operation, if it's high that indicates a READ operation.
+#
+# Later an optional 10bit slave addressing scheme was added.
+#
+# Documentation:
+# http://www.nxp.com/acrobat/literature/9398/39340011.pdf (v2.1 spec)
+# http://www.nxp.com/acrobat/usermanuals/UM10204_3.pdf (v3 spec)
+# http://en.wikipedia.org/wiki/I2C
+#
+
+# TODO: Look into arbitration, collision detection, clock synchronisation, etc.
+# TODO: Handle clock stretching.
+# TODO: Handle combined messages / repeated START.
+# TODO: Implement support for 7bit and 10bit slave addresses.
+# TODO: Implement support for inverting SDA/SCL levels (0->1 and 1->0).
+# TODO: Implement support for detecting various bus errors.
+
+# TODO: Return two buffers, one with structured data for the GUI to parse
+#       and display, and one with human-readable ASCII output.
+
+def sigrokdecode_i2c(inbuf):
+       """I2C protocol decoder"""
+
+       # FIXME: This should be passed in as metadata, not hardcoded here.
+       signals = (2, 5)
+       channels = 8
+
+       o = wr = ack = d = ''
+       bitcount = data = 0
+       state = 'IDLE'
+
+       # Get the bit number (and thus probe index) of the SCL/SDA signals.
+       scl_bit, sda_bit = signals
+
+       # Get SCL/SDA bit values (0/1 for low/high) of the first sample.
+       s = ord(inbuf[0])
+       oldscl = (s & (1 << scl_bit)) != 0
+       oldsda = (s & (1 << sda_bit)) != 0
+
+       # Loop over all samples.
+       # TODO: Handle LAs with more/less than 8 channels.
+       for samplenum, s in enumerate(inbuf[1:]): # We skip the first byte...
+ 
+               s = ord(s) # FIXME
+
+               # Get SCL/SDA bit values (0/1 for low/high).
+               scl = (s & (1 << scl_bit)) != 0
+               sda = (s & (1 << sda_bit)) != 0
+
+               # TODO: Wait until the bus is idle (SDA = SCL = 1) first?
+
+               # START condition (S): SDA = falling, SCL = high
+               if (oldsda == 1 and sda == 0) and scl == 1:
+                       o += "%d\t\tSTART\n" % samplenum
+                       state = 'ADDRESS'
+                       bitcount = data = 0
+
+               # Data latching by transmitter: SCL = low
+               elif (scl == 0):
+                       pass # TODO
+
+               # Data sampling of receiver: SCL = rising
+               elif (oldscl == 0 and scl == 1):
+                       bitcount += 1
+
+                       # o += "%d\t\tRECEIVED BIT %d:  %d\n" % \
+                       #       (samplenum, 8 - bitcount, sda)
+
+                       # Address and data are transmitted MSB-first.
+                       data <<= 1
+                       data |= sda
+
+                       if bitcount != 9:
+                               continue
+
+                       # We received 8 address/data bits and the ACK/NACK bit.
+                       data >>= 1 # Shift out unwanted ACK/NACK bit here.
+                       o += "%d\t\t%s: " % (samplenum, state)
+                       ack = (sda == 1) and 'NACK' or 'ACK'
+                       d = (state == 'ADDRESS') and (data & 0xfe) or data
+                       wr = ''
+                       if state == 'ADDRESS':
+                               wr = (data & 1) and ' (W)' or ' (R)'
+                               state = 'DATA'
+                       o += "0x%02x%s (%s)\n" % (d, wr, ack)
+                       bitcount = data = 0
+
+               # STOP condition (P): SDA = rising, SCL = high
+               elif (oldsda == 0 and sda == 1) and scl == 1:
+                       o += "%d\t\tSTOP\n" % samplenum
+                       state = 'IDLE'
+
+               # Save current SDA/SCL values for the next round.
+               oldscl = scl
+               oldsda = sda
+
+       return o
+
+# This is just a draft.
+def sigrokdecode_register_i2c():
+       metadata = {
+               'id': 'i2c',
+               'name': 'I2C',
+               'description': 'Inter-Integrated Circuit (I2C) bus',
+               'function': 'sigrokdecode_i2c',
+               'inputformats': ['raw'],
+               'signalnames':  {
+                               'SCL': 'Serial clock line',
+                               'SDA': 'Serial data line',
+                               },
+               'ouputformats': ['i2c', 'ascii'],
+       }
+       return metadata
+