spidev library usage in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

SPI Data Transfer Output

What is the output of this code snippet when reading 3 bytes from SPI device?

Raspberry Pi

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 50000
response = spi.xfer2([0x01, 0x02, 0x03])
print(response)
spi.close()

A A list of 3 integers returned by the SPI device

B [0, 0, 0]

C [1, 2, 3]

D SyntaxError

💡 Hint

The xfer2 method sends and receives data simultaneously over SPI.

The xfer2 method sends the list of bytes and returns a list of the same length with bytes received from the SPI device. The exact values depend on the connected device.

🧠 Conceptual

intermediate

SPI Mode Setting Effect

What does setting spi.mode = 3 do in the spidev library?

A Enables 3-wire SPI communication

B Sets the SPI speed to 3 MHz

C Sets clock polarity and phase to mode 3 (CPOL=1, CPHA=1)

D Closes the SPI connection

💡 Hint

SPI mode controls clock polarity and phase.

SPI mode 3 means clock polarity (CPOL) is 1 and clock phase (CPHA) is 1, affecting how data is clocked in and out.

🔧 Debug

advanced

Identify the Error in SPI Initialization

What error will this code raise when run on a Raspberry Pi?

Raspberry Pi

import spidev
spi = spidev.SpiDev()
spi.open(1)
spi.max_speed_hz = 1000000
spi.close()

A TypeError: open() missing 1 required positional argument: 'device'

B AttributeError: 'SpiDev' object has no attribute 'max_speed_hz'

C FileNotFoundError: No such file or directory '/dev/spidev1.0'

D No error, runs successfully

💡 Hint

Check the parameters required by spi.open() method.

The open() method requires two arguments: bus and device. Passing only one argument causes a TypeError.

📝 Syntax

advanced

Correct SPI Write and Read Syntax

Which option correctly writes bytes [0x10, 0x20] and reads 2 bytes back using spidev?

A

spi.write([0x10, 0x20])
response = spi.read(2)

B

spi.writebytes([0x10, 0x20])
response = spi.readbytes(2)

C spi.xfer([0x10, 0x20])

D spi.xfer2([0x10, 0x20])

💡 Hint

xfer2 sends and receives data in one call.

The xfer2 method sends bytes and returns the bytes received simultaneously. writebytes and readbytes are separate calls and may not synchronize correctly.

🚀 Application

expert

SPI Speed Configuration Impact

If you set spi.max_speed_hz = 10000000 on a Raspberry Pi SPI device, what is the most likely outcome?

A The SPI device will enter low power mode

B SPI communication will fail or produce corrupted data because 10 MHz exceeds typical hardware limits

C The Raspberry Pi will automatically reduce speed to the maximum supported frequency

D SPI communication will be stable and faster than 1 MHz

💡 Hint

Check Raspberry Pi SPI hardware maximum speed specifications.

Setting SPI speed too high can cause communication errors or corrupted data because the hardware or connected device cannot handle that speed.