spidev library usage in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the spidev library.

Raspberry Pi

import [1]

Drag options to blanks, or click blank then click option'

Aspidev

Bspi

Cspidev_lib

Dspilib

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect module names like 'spi' or 'spilib'.

The spidev library is imported using import spidev.

2fill in blank

medium

Complete the code to create an SPI object.

Raspberry Pi

spi = [1].SpiDev()

Drag options to blanks, or click blank then click option'

ASPI

Bspidev

Cspi

DSpiDev

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'SPI' or 'SpiDev' as the module name.

You create an SPI object by calling SpiDev() from the spidev module.

3fill in blank

hard

Fix the error in opening SPI bus 0, device 1.

Raspberry Pi

spi.open([1], 1)

Drag options to blanks, or click blank then click option'

A0

B1

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping bus and device numbers or using invalid bus numbers.

The SPI bus number is usually 0 or 1. To open bus 0, device 1, use spi.open(0, 1).

4fill in blank

hard

Fill both blanks to set SPI max speed to 1 MHz and mode to 0.

Raspberry Pi

spi.max_speed_hz = [1]
spi.mode = [2]

Drag options to blanks, or click blank then click option'

A1000000

B500000

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong speed values or wrong mode numbers.

Set max_speed_hz to 1,000,000 for 1 MHz speed and mode to 0 for SPI mode 0.

5fill in blank

hard

Fill all three blanks to write bytes [0x01, 0x02, 0x03] and read response.

Raspberry Pi

response = spi.xfer2([1])
print([2])
[3].close()

Drag options to blanks, or click blank then click option'

A[0x01, 0x02, 0x03]

Bresponse

Cspi

D[1, 2, 3]

Attempts:

3 left

💡 Hint

Common Mistakes

Using decimal list instead of hex, printing wrong variable, or forgetting to close SPI.

Use spi.xfer2([0x01, 0x02, 0x03]) to send bytes and get the response. Then print the response variable. Finally, close the SPI connection with spi.close().

Practice

1. What is the primary purpose of the spidev library on a Raspberry Pi?

easy

A. To communicate with SPI devices by sending and receiving bytes

B. To control the Raspberry Pi's GPIO pins directly

C. To manage Wi-Fi connections on the Raspberry Pi

D. To create graphical user interfaces on the Raspberry Pi

Solution

1. Step 1: Understand the role of spidev

   The spidev library is designed to allow communication with SPI devices by sending and receiving bytes.

2. Step 2: Compare with other options

   Options B, C, and D relate to GPIO, Wi-Fi, and GUI, which are not the main functions of spidev.

3. Final Answer:

   To communicate with SPI devices by sending and receiving bytes -> Option A

4. Quick Check:

   spidev = SPI communication [OK]

Hint: Remember spidev is for SPI device communication only [OK]

Common Mistakes:

• Confusing spidev with GPIO control libraries
• Thinking spidev manages network or GUI tasks
• Assuming spidev handles I2C communication

2. Which of the following is the correct way to open SPI bus 0, device 0 using spidev in Python?

easy

A. spi.connect(0, 0)

B. spi.start(0, 0)

C. spi.init(0, 0)

D. spi.open(0, 0)

Solution

1. Step 1: Recall spidev method to open SPI

   The correct method to open SPI bus and device is open(bus, device).

2. Step 2: Verify method names

   Methods like start, connect, and init are not valid for spidev.

3. Final Answer:

   spi.open(0, 0) -> Option D

4. Quick Check:

   Open SPI with open() method [OK]

Hint: Use spi.open(bus, device) to start SPI communication [OK]

Common Mistakes:

• Using incorrect method names like start or connect
• Confusing open() with init()
• Not specifying both bus and device numbers

3. What will be the output of the following code snippet?

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

medium

A. [1, 2, 3]

B. [0, 0, 0]

C. A list of bytes received from the SPI device

D. SyntaxError

Solution

1. Step 1: Understand spi.xfer2() behavior

   The xfer2() method sends bytes and returns a list of bytes received from the SPI device.

2. Step 2: Analyze the code output

   The output depends on the connected SPI device's response, so it returns a list of received bytes, not necessarily the same as sent.

3. Final Answer:

   A list of bytes received from the SPI device -> Option C

4. Quick Check:

   xfer2() returns received bytes list [OK]

Hint: xfer2() returns device response bytes list [OK]

Common Mistakes:

• Assuming output equals input list
• Expecting zeros if no device connected
• Thinking code causes syntax error

4. Identify the error in this code snippet using spidev:

import spidev
spi = spidev.SpiDev()
spi.xfer2([0x01, 0x02])
spi.open(0, 0)
spi.close()

medium

A. Not closing SPI device after use

B. Calling xfer2() before opening SPI device

C. Using wrong method name xfer2()

D. Missing import statement

Solution

1. Step 1: Check method call order

   The xfer2() method requires the SPI device to be opened first with open().

2. Step 2: Identify the error

   Here, xfer2() is called before open(), causing a runtime error.

3. Final Answer:

   Calling xfer2() before opening SPI device -> Option B

4. Quick Check:

   Open SPI before xfer2() call [OK]

Hint: Always open SPI before using xfer2() [OK]

Common Mistakes:

• Calling xfer2() before open()
• Forgetting to close SPI device
• Confusing method names

5. You want to send the bytes [0x10, 0x20, 0x30] to an SPI device on bus 1, device 0, at 500000 Hz speed, and receive the response. Which code snippet correctly does this using spidev?

hard

A. spi = spidev.SpiDev()
spi.open(1, 0)
spi.max_speed_hz = 500000
response = spi.xfer2([0x10, 0x20, 0x30])
spi.close()
print(response)

B. spi = spidev.SpiDev()
spi.open(0, 1)
spi.speed = 500000
response = spi.xfer([0x10, 0x20, 0x30])
spi.close()
print(response)

C. spi = spidev.SpiDev()
spi.open(1, 0)
spi.max_speed = 500000
response = spi.xfer2([0x10, 0x20, 0x30])
spi.close()
print(response)

D. spi = spidev.SpiDev()
spi.open(1, 0)
spi.max_speed_hz = 500000
response = spi.transfer([0x10, 0x20, 0x30])
spi.close()
print(response)

Solution

1. Step 1: Check SPI open parameters and speed setting

   Bus 1, device 0 is opened with spi.open(1, 0). Speed is set with spi.max_speed_hz = 500000.

2. Step 2: Verify transfer method and closing

   xfer2() is the correct method to send and receive bytes. The device is closed after communication.

3. Final Answer:

   Correct code snippet with spi.open(1, 0), max_speed_hz, xfer2(), and close() -> Option A

4. Quick Check:

   Use open(1,0), max_speed_hz, xfer2(), close() [OK]

Hint: Set max_speed_hz and use xfer2() after open() [OK]

Common Mistakes:

• Using wrong bus/device numbers
• Setting speed with wrong attribute name
• Using incorrect transfer method name
• Not closing SPI device