ESP32 SPI Peripherals

The ESP32 includes four SPI controllers, but only two of them: SPI2 and SPI3 are available for general use. These are commonly known as HSPI and VSPI. The other two SPI controllers, SPI0 and SPI1, are reserved for internal usage.

On the ESP32, many GPIO pins are designed to be reused for different functions. For example, one pin might be used as a general-purpose digital output in one application, or as an SPI clock line in another. This is called multiplexing. It means a single physical pin can be connected to different internal signals, depending on how you configure it in your code.

The ESP32 has a few GPIO pins that are directly connected to each SPI controller. These are:

• For HSPI (SPI2): GPIO2, GPIO4, and GPIO12 to GPIO15

• For VSPI (SPI3): GPIO5, GPIO18, GPIO19, and GPIO21 to GPIO23

These pins are wired in the chip to work efficiently with SPI and are commonly used. However, the ESP32 also allows you to reassign the SPI signals to many other GPIOs.

Here are the default SPI pin assignments for the ESP32 Devkit:

Using SPI in esp-hal

To use SPI in the esp-hal crate, we create and configure the SPI interface with the pins we want. Here is an example that uses the SPI2 bus.

#![allow(unused)]
fn main() {
use esp_hal::spi::master::Config as SpiConfig;
use esp_hal::spi::master::Spi;
use esp_hal::spi::Mode as SpiMode;

// Initialize SPI
let spi_bus = Spi::new(
    peripherals.SPI2,
    SpiConfig::default()
        .with_frequency(Rate::from_mhz(60))
        .with_mode(SpiMode::_0),
)
.unwrap()
//CLK
.with_sck(peripherals.GPIO18)
//DIN
.with_mosi(peripherals.GPIO23);
let cs = Output::new(peripherals.GPIO15, Level::Low, OutputConfig::default());
}

Example Driver Usage

Now that we have the SPI interface set up, let's use it to talk to an SD card using the embedded_sdmmc crate. We will use ExclusiveDevice from the embedded-hal-bus crate.

#![allow(unused)]
fn main() {
use embedded_hal_bus::spi::ExclusiveDevice;
use embedded_sdmmc::SdCard;
use esp_hal::delay::Delay;

//  Gets exclusive access to the SPI bus (not shared).
let spi_dev = ExclusiveDevice::new(spi_bus, cs, Delay).unwrap();

// Initialize the SD Card driver with SPI Device
let sdcard = SdCard::new(spi_dev, Delay);
}