stm32 adc g4: example of async read

Signed-off-by: Ivan Li <ivanli2048@gmail.com>

examples/stm32g4/src/bin/adc_dma.rs

@@ -0,0 +1,60 @@
+#![no_std]
+#![no_main]
+
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_stm32::adc::{Adc, AdcChannel as _, SampleTime};
+use embassy_stm32::Config;
+use embassy_time::Timer;
+use {defmt_rtt as _, panic_probe as _};
+
+static mut DMA_BUF: [u16; 2] = [0; 2];
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let mut read_buffer = unsafe { &mut DMA_BUF[..] };
+
+    let mut config = Config::default();
+    {
+        use embassy_stm32::rcc::*;
+        config.rcc.pll = Some(Pll {
+            source: PllSource::HSI,
+            prediv: PllPreDiv::DIV4,
+            mul: PllMul::MUL85,
+            divp: None,
+            divq: None,
+            // Main system clock at 170 MHz
+            divr: Some(PllRDiv::DIV2),
+        });
+        config.rcc.mux.adc12sel = mux::Adcsel::SYS;
+        config.rcc.sys = Sysclk::PLL1_R;
+    }
+    let p = embassy_stm32::init(config);
+
+    info!("Hello World!");
+
+    let mut adc = Adc::new(p.ADC1);
+
+    let mut dma = p.DMA1_CH1;
+    let mut vrefint_channel = adc.enable_vrefint().degrade_adc();
+    let mut pa0 = p.PA0.degrade_adc();
+
+    loop {
+        adc.read(
+            &mut dma,
+            [
+                (&mut vrefint_channel, SampleTime::CYCLES247_5),
+                (&mut pa0, SampleTime::CYCLES247_5),
+            ]
+            .into_iter(),
+            &mut read_buffer,
+        )
+        .await;
+
+        let vrefint = read_buffer[0];
+        let measured = read_buffer[1];
+        info!("vrefint: {}", vrefint);
+        info!("measured: {}", measured);
+        Timer::after_millis(500).await;
+    }
+}