Revise I2S interface to ring-buffered.

examples/stm32f4/src/bin/i2s_dma.rs

@@ -1,13 +1,10 @@
 #![no_std]
 #![no_main]
 
-use core::fmt::Write;
-
 use defmt::*;
 use embassy_executor::Spawner;
 use embassy_stm32::i2s::{Config, I2S};
 use embassy_stm32::time::Hertz;
-use heapless::String;
 use {defmt_rtt as _, panic_probe as _};
 
 #[embassy_executor::main]
@@ -15,6 +12,8 @@ async fn main(_spawner: Spawner) {
     let p = embassy_stm32::init(Default::default());
     info!("Hello World!");
 
+    let mut dma_buffer = [0x00_u16; 128];
+
     let mut i2s = I2S::new_txonly(
         p.SPI2,
         p.PC3,  // sd
@@ -22,13 +21,13 @@ async fn main(_spawner: Spawner) {
         p.PB10, // ck
         p.PC6,  // mck
         p.DMA1_CH4,
+        &mut dma_buffer,
         Hertz(1_000_000),
         Config::default(),
     );
 
-    for n in 0u32.. {
-        let mut write: String<128> = String::new();
-        core::write!(&mut write, "Hello DMA World {}!\r\n", n).unwrap();
-        i2s.write(&mut write.as_bytes()).await.ok();
+    for i in 0_u16.. {
+        i2s.write(&mut [i * 2; 64]).await.ok();
+        i2s.write(&mut [i * 2 + 1; 64]).await.ok();
     }
 }