Decoding UART protocol (FPGA acquisition)

Description

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

Here are the possible values for the decoder:

  • baudrate - 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600

  • bit order - LSB_FIRST = 0, MSB_FIRST = 1

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

  • number of data bits - 5, 6, 7, 8, 9

  • number of stop bits - STOP_BITS_NO = 0, STOP_BITS_05 = 1, STOP_BITS_10 = 2, STOP_BITS_15 = 3, STOP_BITS_20 = 4

  • parity - NONE = 0, EVEN = 1, ODD = 2, ALWAYS_0 = 3, ALWAYS_1 = 4

  • 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:

  • Parity bit error - the parity bit of the UART message is not detected (control value 0)

  • Start bit error - the start bit of the UART message is not detected (control value 1)

  • Stop bit error - the stop bit of the UART message is not detected (control value 2)

  • Data - the data bits of the UART message (control value 3)

  • Start bit - the start bit of the UART message (control value 4)

  • Stop ok - the stop bit of the UART message (control value 5)

  • Parity bit - the parity bit of the UART message (control value 6)

Each 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.

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

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

Required hardware

  • Red Pitaya

  • pin jumper wires

../../../_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 UART 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)

## UART decoder settings ##
baudrate = 921600                   # 1200,2400,4800,9600,19200,38400,57600,115200,230400,576000,921600
bit_order = 0                       # LSB_FIRST = 0, MSB_FIRST = 1
invert = 0
num_data_bits = 8                   # 5, 6, 7, 8, 9
num_stop_bits = 1                   # STOP_BITS_NO = 0, STOP_BITS_05 = 1, STOP_BITS_10 = 2, STOP_BITS_15 = 3, STOP_BITS_20 = 4
parity = 2                          # NONE = 0, EVEN = 1, ODD = 2, ALWAYS_0 = 3, ALWAYS_1 = 4
rx_line = 5                         # UART RX (1 - first line.  Valid values are from 1 to 8)
tx_line = 6                         # UART TX

# LA acquisition
trigger_ch = rp_la.LA_T_CHANNEL_5               # Trigger chanels are 1 to 8
trig_edge = rp_la.LA_RISING_OR_FALLING          # LA_LOW, LA_HIGH, LA_RISING, LA_FALLING, LA_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(enable_RLE)
rp_cla.setDecimation(decimation)
rp_cla.setTrigger(trigger_ch, trig_edge)
rp_cla.setPreTriggerSamples(pre_trig_samples)
rp_cla.setPostTriggerSamples(post_trig_samples)

# Add UART decoder and configure settings
rp_cla.addDecoder("UART", rp_la.LA_DECODER_UART)
rp_cla.setDecoderSettingsUInt("UART", "acq_speed", acq_rate)
rp_cla.setDecoderSettingsUInt("UART", "baudrate", baudrate)
rp_cla.setDecoderSettingsUInt("UART", "bitOrder", bit_order)
rp_cla.setDecoderSettingsUInt("UART", "invert", invert)
rp_cla.setDecoderSettingsUInt("UART", "num_data_bits", num_data_bits)
rp_cla.setDecoderSettingsUInt("UART", "num_stop_bits", num_stop_bits)
rp_cla.setDecoderSettingsUInt("UART", "parity", parity)
rp_cla.setDecoderSettingsUInt("UART", "rx", rx_line)
rp_cla.setDecoderSettingsUInt("UART", "tx", tx_line)

# 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("uart_data.bin")

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

# Get 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("UART")
for index in range(len(decode)):
    print(rp_cla.getAnnotation(rp_la.LA_DECODER_UART, decode[index]['control']), " = ", decode[index])

# Release resources
del rp_cla