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dianjixz
77 lines
3.1 KiB
Markdown
77 lines
3.1 KiB
Markdown
## SPI
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Serial Peripheral Interface (SPI) is a common serial communication protocol used for high-speed data transfer between external devices such as microcontrollers, sensors, and storage devices.
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Here are some important concepts about SPI that beginners need to understand:
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1. **Serial Communication:** SPI is a serial communication protocol that allows devices to transmit multiple bits of data at the same time, enabling high-speed data transfer.
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2. **Master-Slave Structure:** SPI communication involves two types of devices: master and slave. The master device generates the clock signal and controls the communication, while the slave device responds to the master device's commands.
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3. **Communication Lines:** SPI uses multiple lines for communication:
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- SCLK (Serial Clock): The clock signal generated by the master device for synchronizing data transfer.
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- MOSI (Master Out Slave In): The line for sending data from the master device to the slave device.
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- MISO (Master In Slave Out): The line for sending data from the slave device to the master device.
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- SS/CS (Slave Select/Chip Select): Used for selecting the slave device's line, allowing communication between multiple devices.
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4. **Clock Synchronization:** Data transfer in SPI communication is synchronous, meaning data is transmitted based on the clock signal.
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5. **Frame Format:** SPI communication consists of a series of data frames. Data transfer usually occurs at each clock cycle, enabling high-speed transmission.
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6. **Speed:** SPI communication can be very fast because data transfer is synchronous. The speed can be set according to requirements.
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7. **Full Duplex:** SPI is a full-duplex communication protocol, allowing simultaneous bidirectional data transfer.
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8. **Applications:** SPI is widely used in embedded systems, storage devices, sensors, displays, communication devices, and other fields.
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examples:
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```c
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//-----------------------------------------------------------------------------
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#include "linux_spi/linux_spi.h"
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#include <stdio.h>
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//-----------------------------------------------------------------------------
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#define SPI_DEVICE "/dev/spidev0.0"
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//-----------------------------------------------------------------------------
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int main()
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{
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spi_t spi;
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char buf[1024];
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int i;
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int retv = spi_init(&spi,
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SPI_DEVICE, // filename like "/dev/spidev0.0"
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0, // SPI_* (look "linux/spi/spidev.h")
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0, // bits per word (usually 8)
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2500000); // max speed [Hz]
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printf(">>> spi_init() return %d\n", retv);
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retv = spi_read(&spi, buf, 1024);
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printf(">>> spi_read(1024) return %d\n", retv);
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for (i = 0; i < 1024; i++)
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buf[i] = 0x55;
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retv = spi_write(&spi, buf, 1024);
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printf(">>> spi_write(1024) return %d\n", retv);
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spi_free(&spi);
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return 0;
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}
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```
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When compiling the above program, you can compile and run it in the examples/linux_spi directory of [M5Stack_Linux_Libs]().
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Enter the Linux device:
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``` bash
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# Clone repository
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git clone https://github.com/M5STACK/M5Stack_Linux_Libs.git
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# Enter directory
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cd M5Stack_Linux_Libs/examples/linux_spi
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# Compile
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scons
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``` |