Decoding CAN protocol (FPGA acquisition)

Description

This example demonstrates how to decode the CAN protocol using logic analyser commands. Red Pitaya captures data on the specified digital inputs and decodes it. The captured data is stored in the “can_data.bin” file, which can be used for further analysis. When configuring the example, make sure that the captured CAN settings match the CAN decoder settings.

Here are the possible values for the decoder:

  • address_format - Shifted = 0, Unshifted = 1

  • invert_bit - 0, 1 (invert input data signal)

  • decoder lines - 1 - 8 (1 == DIO0_P)

  • trigger channel - LA_T_CHANNEL_1 - LA_T_CHANNEL_8 (1 == DIO0_P)

The possible decoded data packet types are:

  • Payload data - Data payload (control value 0)

  • Start of frame - Start of frame (SOF) bit, must be dominant (control value 1)

  • End of frame - End of frame (EOF) bit, must be recessive (control value 2)

  • Identifier - Identifier bits (control value 3)

  • Extended identifier - Extended identifier bits (control value 4)

  • Full identifier - Full identifier bits (control value 5)

  • Identifier extension bit - Identifier extension bit (control value 6)

  • Reserved bit 0 and 1 - (control value 7)

  • Substitute remote request - Substitute remote request (SRR) bit (control value 8)

  • Data length count - Data length count bits (control value 9)

  • CRC delimiter - CRC delimiter bit (control value 10)

  • ACK slot - ACK slot bit (control value 11)

  • ACK delimiter - ACK delimiter bit (control value 12)

  • Stuff bit - Stuff bit (control value 13)

  • End of frame (EOF) must be 7 recessive bits - (control value 14)

  • Identifier bits 10..4 must not be all recessive - (control value 15)

  • CRC delimiter must be recessive - (control value 16)

  • ACK delimiter must be recessive - (control value 17)

  • Bit rate switch - Bit rate switch (control value 18)

  • Error state indicator - Error state indicator (control value 19)

  • Flexible data - Flexible data (control value 20)

  • Stuff bit error - Stuff bit error (control value 21)

  • CRC-15 - CRC-15 (control value 22)

  • CRC-17 - CRC-17 (control value 23)

  • CRC-21 - CRC-21 (control value 24)

  • Fixed stuff bit - Fixed stuff bit (control value 25)

  • Stuff bits - (control value 26)

  • SBC + FSB + CRC - (control value 27)

Each decoded data packet has the following parameters:

  • control - Data identifier.

  • data - Data contained in the protocol.

  • line name - Line name according to the protocol for which the data was decoded. Must be specified in the decoder settings, otherwise they will not be present.

  • sampleStart - Starting position in the data to be recognized in samples. 0 = first sample, 1 = second sample, etc. The value is not an integer, since the bit width can be real depending on the protocol. Includes the pretrigger samples.

  • length - Length of the recognized block in samples.

    \[\text{l_{packet}} = \frac{125~\mathrm{MHz}}{\text{decimation} \cdot \text{can_speed}} \cdot \text{bitsInPack}\]

  • bitsInPack - Number of recognized data bits. Multiple of 0.5.

Required hardware

Without the CAN transceiver, the CAN protocol cannot be decoded.

../../../_images/RedPitaya_general.png

Required software

  • IN DEV - Nightly Build OS

Note

This code is written for IN DEV and will not work with the currently available OS releases. To use this functionality, please install the Nightly Build OS versions.

API Code Examples

Code - Python

#!/usr/bin/python3
""" Example of using the Logic Analyzer Python API to decode an external CAN signal on Red Pitaya.
"""

import sys
import time
import rp_la
import rp_hw_profiles
import numpy as np
from rp_overlay import overlay

# Define callback
class Callback(rp_la.CLACallback):
    def captureStatus(self, controller, isTimeout, bytes, samples, preTrig, postTrig):
        print("CaptureStatus timeout =", isTimeout, "bytes =", bytes, "samples =", samples, "preTrig =", preTrig, "postTrig =", postTrig)

    def decodeDone(self, controller, name):
        print("Decode done ", name)

# CAN decoder settings
can_decoder = "CAN"
dec_fast_bitrate = 2000000
dec_invert_bit = 0
dec_nominal_bitrate = 200000
dec_rx = 1
dec_sample_point = 87

# LA acquisition
trigger_ch = rp_la.LA_T_CHANNEL_1               # Trigger chanels are 1 to 8
trig_edge = rp_la.LA_RISING_OR_FALLING          # LOW, HIGH, RISING, FALLING, RISING_OR_FALLING

enable_RLE = True
decimation = 16
acq_rate = int(rp_hw_profiles.rp_HPGetBaseSpeedHzOrDefault() / decimation)
pre_trig_samples = int(125e6/decimation * 1e-3)
post_trig_samples = int(125e6/decimation * 3e-3)
print(f"Pre post trigger: {pre_trig_samples} {post_trig_samples}")


# Change FPGA image to logic analyzer "logic"
fpga = overlay("logic")

# Create controller and initialize FPGA
rp_cla = rp_la.CLAController()
rp_cla.initFpga()

callback = Callback()
rp_cla.setDelegate(callback.__disown__())

# Set LA parameters
rp_cla.setEnableRLE(True)
rp_cla.setDecimation(decimation)
rp_cla.setTrigger(trigger_ch, trig_edge)
rp_cla.setPreTriggerSamples(pre_trig_samples)
rp_cla.setPostTriggerSamples(post_trig_samples)

# Add I2C decoder and configure settings
rp_cla.addDecoder(can_decoder, rp_la.LA_DECODER_CAN)
rp_cla.setDecoderSettingsUInt(can_decoder, "acq_speed", acq_rate)
rp_cla.setDecoderSettingsUInt(can_decoder, "invert_bit", dec_invert_bit)
rp_cla.setDecoderSettingsUInt(can_decoder, "fast_bitrate", dec_fast_bitrate)
rp_cla.setDecoderSettingsUInt(can_decoder, "nominal_bitrate", dec_nominal_bitrate)
rp_cla.setDecoderSettingsUInt(can_decoder, "rx", dec_rx)
rp_cla.setDecoderSettingsUInt(can_decoder, "sample_point", dec_sample_point)

print(f"CAN decoder settings: {rp_cla.getDecoderSettings(f'{can_decoder}')}")

# Start acquisition
rp_cla.runAsync(0)
print("Started data acquisition")

time.sleep(0.1)             # Wait for LA to acquire some data

# Wait for trigger
res = rp_cla.wait(0)        # No timeout set
if res:
    print("Exit by timeout")
    sys.exit(1)

# Save data to file
rp_cla.saveCaptureDataToFile("can_data.bin")

# Get captured data
rawBytesCount = rp_cla.getCapturedDataSize()
raw_data = np.zeros(rawBytesCount, dtype=np.uint8)
print(f"Packed samples count: {rp_cla.getDataNP(raw_data)}")

# Get unpacked RLE data
rle_data = np.zeros(rp_cla.getCapturedSamples(), dtype=np.uint8)
print(f"Unpacked samples count: {rp_cla.getUnpackedRLEDataNP(rle_data)}")
print(f"RLE DATA {raw_data}")
print(f"UNPACKED DATA {rle_data}\n")

rp_cla.printRLE(False)

print("\nDecoded data")
decode = rp_cla.getDecodedData(can_decoder)
for index in range(len(decode)):
    print(f"{rp_cla.getAnnotation(rp_la.LA_DECODER_CAN, decode[index]['control'])} = {decode[index]}")

# Close the interface and release resources
print("End Program")
del rp_cla