spidev library usage in Raspberry Pi - Step-by-Step Execution

Concept Flow - spidev library usage

Import spidev

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Create SPI object

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Open SPI bus and device

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Set SPI parameters (mode, speed)

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Transfer data (write/read)

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Close SPI connection

This flow shows how to use spidev: import, open SPI bus, set parameters, transfer data, then close.

Execution Sample

Raspberry Pi

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

This code opens SPI bus 0 device 0, sets speed, sends 3 bytes, receives response, then closes SPI.

Execution Table

Step	Action	SPI Object State	Data Sent	Data Received	Notes
1	Import spidev	No SPI object yet	-	-	Library ready to use
2	Create SPI object	spi created, not open	-	-	spi = spidev.SpiDev()
3	Open SPI bus 0, device 0	spi open on bus 0, device 0	-	-	spi.open(0, 0)
4	Set max speed to 50000 Hz	spi max_speed_hz=50000	-	-	spi.max_speed_hz = 50000
5	Transfer data [0x01,0x02,0x03]	spi open	[1, 2, 3]	[response bytes]	spi.xfer2 sends and receives data
6	Close SPI connection	spi closed	-	-	spi.close()
7	End	spi closed	-	-	No further SPI communication

💡 SPI connection closed, no more data transfer possible

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6
spi	None	SpiDev object created	Opened on bus 0, device 0	max_speed_hz=50000 set	Data transferred, response stored	Closed

Key Moments - 3 Insights

Why do we need to call spi.open(0, 0) before transferring data?

Because spi.open(0, 0) connects to the specific SPI bus and device. Without opening, the SPI object can't communicate. See execution_table step 3 and 5.

What does spi.xfer2([0x01, 0x02, 0x03]) do exactly?

It sends the list of bytes [1, 2, 3] over SPI and simultaneously reads the response bytes from the device. See execution_table step 5.

Why should we call spi.close() at the end?

Closing releases the SPI device so other programs can use it and cleans up resources. See execution_table step 6.

Visual Quiz - 3 Questions

Look at the execution_table at step 5, what data is sent over SPI?

A [1, 2, 3]

B [0x00, 0x00, 0x00]

C [255, 255, 255]

D No data sent

💡 Hint

Check the 'Data Sent' column at step 5 in the execution_table.

At which step is the SPI bus actually opened for communication?

A Step 2

B Step 4

C Step 3

D Step 6

💡 Hint

Look at the 'Action' and 'SPI Object State' columns in execution_table.

If we skip spi.close(), what happens according to the execution flow?

A Data transfer fails

B SPI connection remains open, possibly blocking others

C SPI bus closes automatically immediately

D Program crashes

💡 Hint

Refer to key_moments about why spi.close() is important.

Concept Snapshot

spidev usage steps:
1. import spidev
2. create spi object
3. open SPI bus/device
4. set parameters (speed, mode)
5. transfer data with xfer2()
6. close SPI connection
Always open before transfer and close after done.

Full Transcript

This visual execution shows how to use the spidev library on Raspberry Pi. First, import spidev and create an SPI object. Then open the SPI bus and device you want to communicate with. Set parameters like max speed. Use xfer2() to send and receive data bytes. Finally, close the SPI connection to free resources. The execution table traces each step, showing the SPI object's state and data sent or received. Key moments clarify why opening and closing are necessary and how data transfer works. The quiz tests understanding of these steps and their order.