spi

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There is no standard `spi` command with a general-purpose synopsis in Linux. Interactions with SPI hardware are typically done programmatically through device files and system calls, or via specialized tools provided by hardware vendors or specific projects.

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    Since 'spi' is not a standard command, there are no predefined command-line parameters. Any parameters would be specific to custom applications or scripts designed to interact with SPI hardware.

The term "spi" in the Linux context typically refers to the Serial Peripheral Interface (SPI) bus, a synchronous serial data link standard widely used for short-distance communication, primarily in embedded systems. It is not a standalone command-line utility found in standard Linux distributions similar to "ls" or "grep".

Instead, interaction with SPI hardware devices on a Linux system is managed through the kernel's SPI subsystem. Userspace applications generally communicate with SPI devices via specific kernel modules like spidev, which exposes the SPI bus as device files (e.g., /dev/spidev0.0). Applications then use system calls, primarily ioctl(), to configure the bus (e.g., clock speed, mode, bits per word) and transfer data. This approach requires custom programming (e.g., in C or Python) rather than invoking a generic "spi" command.

Confusing 'spi' (the hardware interface) with a direct command-line utility is a common misconception. Direct manipulation of SPI devices typically requires root privileges and careful programming to avoid hardware damage or unintended behavior. The specific device file paths (e.g., /dev/spidevX.Y) and the available ioctl commands depend on the kernel configuration and the specific SPI controller hardware.

To communicate with an SPI device from userspace, a program typically opens the corresponding /dev/spidevX.Y device file. It then uses ioctl() calls to configure the SPI mode, clock speed, bit order, and bits per word. Data transfer is then performed using ioctl(SPI_IOC_MESSAGE) or sometimes read()/write() for simpler cases. This requires programming in languages like C, C++, Python (using libraries like spidev-py), or Rust.

SPI is extensively used for connecting microcontrollers to peripherals such as SD card readers, EEPROMs, flash memory, real-time clocks, ADCs (Analog-to-Digital Converters), DACs (Digital-to-Analog Converters), and various sensors (e.g., accelerometers, gyroscopes, temperature sensors). It's also frequently used for driving small LCD/OLED displays.

The Serial Peripheral Interface (SPI) was developed by Motorola in the mid-1980s. Its simplicity, full-duplex communication, and high speed made it popular for embedded systems. Linux kernel support for SPI has evolved significantly, with dedicated drivers for various SPI controllers and devices. The spidev module became a common way to expose the SPI bus to userspace, abstracting the complex hardware interactions and providing a standardized interface for application developers.

ioctl(2), open(2), read(2), write(2), sysfs(5), gpio(7)