Why is SPI not working on any of my Raspis?

Question

I tried it on both Raspi 3 and 2 using the SpiDev python library.

I've never even seen any kind of output on MOSI or CS lines with my oscilloscope.

Controlling an SH1106 OLED display via the luma.oled lib works however AND generates signals on the MOSI line.

Also, manually driving the GPIOs works just fine.

Answer 1

You might like to try my little test program, under GUI Desktop IDLE python. Or run under terminal mode with sudo.

# spi_test05 tlfong01 2019apr07hkt2043 ***

# Computer = Rpi3B+
# Linux    = $ hostnamectl = raspberrypi Raspbian GNU/Linux 9 (stretch) Linux 4.14.34-v7+ arm 
# Python   = >>> sys.version = 3.5.3 Jan 19 2017

# Test 1   - repeatSendByte() - SPI port repeatedly send out single bytes.  
# Function - Repeat many times sending a byte, pause after each byte.

# Test 2   - loopBackTest()   - SPI port send and receive one byte.
# Function - Send one byte to MSOI and read it back from MISO. 
# Setup    - Connet MOSI pin to MISO pin to form a loop.

from   time import sleep
import spidev

spiPort0 = spidev.SpiDev()
spiPort0.open(0,0)
spiPort0.max_speed_hz = 100000

def spiSendRecvOneByte(spiPort, sendByte):
    sendByteArray = [sendByte]
    recvByteArray = spiPort.xfer(sendByteArray)    
    return recvByteArray

def repeatSendOneByte(spiPort, sendByte, pauseTimeBetweenBytes, repeatCount):
    print('\nBegin repeatSendByte(),....')
    for i in range(repeatCount):
        spiSendRecvOneByte(spiPort, sendByte)
        sleep(pauseTimeBetweenBytes)
    print('End   repeatSendByte().')
    return

def loopBackOneByte(spiPort, sendByte):
    recvByteArray     = spiSendRecvOneByte(spiPort, sendByte)
    recvByte          = recvByteArray[0]

    print('\nBegin testLoopbackOneByte(),....')
    #print('')
    print('      sendByte  = ', hex(sendByte))
    print('      recvByte  = ', hex(recvByte))
    #print('')
    print('End   testLoopbackOneByte(),....')
    return

def testRepeatSendOneByte():
    repeatSendOneByte(spiPort0, 0x5b, 0.0001, 20000000)
    return

def testLoopbackOneByte():
    loopBackOneByte(spiPort0, 0x5b)
    return

testRepeatSendOneByte()
#testLoopbackOneByte()

''' Smple output tlfong 01 2019apr07hkt2047
Begin testLoopbackOneByte(),....
      sendByte  =  0x5b
      recvByte  =  0x5b
End   testLoopbackOneByte(),....
'''

# *** End ***

Appendices

Appendix A - Rpi SPI pinout

Answer 2

Check /etc/modules. It should contain line spi-dev to enable spi in python:

pi@raspberrypi:~/adxl345spi $ cat /etc/modules
# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
spi-dev
i2c-dev