get_adc_channel_blocking: pass everything by-value to make it compile

Still not really the final solution…

src/main.rs

@@ -19,7 +19,6 @@ use panic_halt as _;
 use rp2040_hal as hal;
 
 // Some traits we need
-use cortex_m::singleton;
 use embedded_hal::PwmPin;
 use fugit::RateExtU32;
 use rp2040_hal::clocks::Clock;
@@ -54,6 +53,28 @@ const HIGH: u16 = 25000;
 /// if your board has a different frequency
 const XTAL_FREQ_HZ: u32 = 12_000_000u32;
 
+fn get_adc_channel_blocking<S, E>(dma: hal::dma::Channels, spi: rp2040_hal::Spi<rp2040_hal::spi::Enabled, S, 8>, cs_pin: &mut dyn embedded_hal::digital::v2::OutputPin<Error = E>) -> u16
+where
+    S: hal::spi::SpiDevice,
+    E: core::fmt::Debug
+{
+    static TX_BUF: [u8; 3] = [0x06, 0x40, 0x00];
+    static mut RX_BUF: [u8; 3] = [0; 3];
+
+    // clear chip select
+    cs_pin.set_low().unwrap();
+
+    // Use BidirectionalConfig to simultaneously write to spi from tx_buf and read into rx_buf
+    unsafe { // necessary due to mutable-static use
+        let transfer = bidirectional::Config::new((dma.ch0, dma.ch1), &TX_BUF, spi, &mut RX_BUF).start();
+        // Wait for both DMA channels to finish
+        let ((_ch0, _ch1), _tx_buf, _spi, _rx_buf) = transfer.wait();
+        cs_pin.set_high().unwrap();
+
+        (((RX_BUF[1] & 0x0F) as u16) << 8) | RX_BUF[2] as u16
+    }
+}
+
 /// Entry point to our bare-metal application.
 ///
 /// The `#[rp2040_hal::entry]` macro ensures the Cortex-M start-up code calls this function
@@ -170,19 +191,10 @@ fn main() -> ! {
     let dma = pac.DMA.split(&mut pac.RESETS);
 
     // Use DMA to read ADC (0xC0 in byte 1 is the channel mask)
-    let tx_buf = singleton!(: [u8; 3] = [0x06, 0x40, 0x00]).unwrap();
-    let rx_buf = singleton!(: [u8; 3] = [0; 3]).unwrap();
+    //let tx_buf = singleton!(: [u8; 3] = [0x06, 0x40, 0x00]).unwrap();
+    //let rx_buf = singleton!(: [u8; 3] = [0; 3]).unwrap();
 
-    // clear chip select
-    spi_cs.set_low().unwrap();
-
-    // Use BidirectionalConfig to simultaneously write to spi from tx_buf and read into rx_buf
-    let transfer = bidirectional::Config::new((dma.ch0, dma.ch1), tx_buf, spi, rx_buf).start();
-    // Wait for both DMA channels to finish
-    let ((_ch0, _ch1), tx_buf, _spi, rx_buf) = transfer.wait();
-    spi_cs.set_high().unwrap();
-
-    let adc_value = (((rx_buf[1] & 0x0F) as u16) << 8) | rx_buf[2] as u16;
+    let adc_value = get_adc_channel_blocking(dma, spi, &mut spi_cs);
 
     {
         let data: String<16> = String::from(adc_value);