Decoding SPI protocol (from file)

Description

This example demonstrates how to decode the SPI protocol using logic analyser commands. Red Pitaya loads the SPI data from the “spi_data.bin” file and decodes it. When configuring the example, make sure that the SPI decoder settings match the capture settings.

Here are the possible values for the decoder:

  • bit order - MSB_FIRST = 0, LSB_FIRST = 1

  • cpha - 0, 1

  • cpol - 0, 1

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

  • number of data bits - 7, 8

  • cs polarity - ActiveLow = 0, ActiveHigh = 1

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

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

Note

Here is a conversion between Red Pitaya SPI modes and CPHA and CPOL:

  • LISL - Low idle level, sample on leading edge - cpol=0, cpha=0

  • LIST - Low idle level, sample on trailing edge - cpol=0, cpha=1

  • HISL - High idle level, sample on leading edge - cpol=1, cpha=0

  • HIST - High idle level, sample on trailing edge - cpol=1, cpha=1

The possible decoded data packet types are:

  • Data - the data bits of the SPI message (control value 0)

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.

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

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

Note

Red Pitaya API SPI speed is rouded to the nearest programmable value. For 1 MHz, the actual speed is SPI clock speed 781250 Hz.

Required hardware

  • Red Pitaya

../../../_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 for decoding LA SPI data from file. Settings are also loaded from a file.
"""
import rp_la

rp_cla = rp_la.CLAController()

rp_cla.loadFromFile("spi_data.bin", True, 0)

rp_cla.addDecoder("SPI", rp_la.LA_DECODER_SPI)
f = open("spi_settings.json", "r", encoding='utf-8')
rp_cla.setDecoderSettings("SPI", f.read())

print("Settings:")
print(rp_cla.getDecoderSettings("SPI"))

print("\nDecoded data\n")
decode = rp_cla.decode("SPI")
for index in range(len(decode)):
    print(rp_cla.getAnnotation(rp_la.LA_DECODER_SPI,decode[index]['control'])," = ",decode[index])
del rp_cla

Modifying decoder settings

#!/usr/bin/python3
"""This script demonstrates how to modify the settings of the SPI decoder in the json files."""

import json
import rp_hw_profiles
import rp_la

# 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)

spi_decoder = "SPI"

decimation = 16
acq_rate = int(rp_hw_profiles.rp_HPGetBaseSpeedHzOrDefault() / decimation)

# Create controller
rp_cla = rp_la.CLAController()

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

# LA FPGA must be loaded/LA Application must be open
rp_cla.initFpga()

# Add decoders
rp_cla.addDecoder(spi_decoder, rp_la.LA_DECODER_SPI)

# Get settings from Red Pitaya
spi_settings = rp_cla.getDecoderSettings(spi_decoder)
print(f"SPI decoder settings: {spi_settings}")

# Modify settings
spi_settings = json.loads(spi_settings)

## SPI decoder settings ##
# - LISL - Low  idle level, sample on leading edge  - cpol=0, cpha=0
# - LIST - Low  idle level, sample on trailing edge - cpol=0, cpha=1
# - HISL - High idle level, sample on leading edge  - cpol=1, cpha=0
# - HIST - High idle level, sample on trailing edge - cpol=1, cpha=1

spi_settings["acq_speed"  ] = acq_rate      # Acquisition speed =! decimation setting
spi_settings["bit_order"  ] = 0             # MsbFirst = 0, LsbFirst = 1
spi_settings["cpha"       ] = 0             # 0, 1
spi_settings["cpol"       ] = 0             # 0, 1
spi_settings["cs_polarity"] = 0             # ActiveLow = 0, ActiveHigh = 1
spi_settings["invert_bit" ] = 0
spi_settings["word_size"  ] = 8             # 7, 8
spi_settings["clk"        ] = 3             # SPI CLK   (1 - first line.  Valid values are from 1 to 8), 0 == disabled
spi_settings["cs"         ] = 4             # SPI CS
spi_settings["miso"       ] = 1             # SPI MISO
spi_settings["mosi"       ] = 2             # SPI MOSI

# Save json data to a file
with open("spi_settings.json", "w", encoding='utf8') as json_file:
    json.dump(spi_settings, json_file, indent=4)

del rp_cla

Save decoder settings to a json file

#!/usr/bin/python3
"""This script demonstrates how to save the settings of the SPI decoder to a json file."""

import json
import rp_la

# 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)

# Create controller
rp_cla = rp_la.CLAController()
callback = Callback()
rp_cla.setDelegate(callback.__disown__())

# LA FPGA must be loaded/LA Application must be open
rp_cla.initFpga()

# Add decoders
rp_cla.addDecoder("SPI", rp_la.LA_DECODER_SPI)

# Get settings from Red Pitaya
spi_settings = rp_cla.getDecoderSettings("SPI")

print(f"SPI decoder settings: {spi_settings}")

# Save json data to a file
spi_settings = json.loads(spi_settings)
with open("spi_settings.json", "w", encoding='utf8') as json_file:
    json.dump(spi_settings, json_file, indent=4)

del rp_cla