diff --git a/bluepill-rs/src/main.rs b/bluepill-rs/src/main.rs
index b13fbb8..c9c0166 100644
--- a/bluepill-rs/src/main.rs
+++ b/bluepill-rs/src/main.rs
@@ -5,10 +5,10 @@
 mod i2c_reg_slave;
 mod i2c_slave;
 
+use panic_halt as _;
+
 #[rtic::app(device = stm32f1::stm32f103, peripherals = true)]
 mod app {
-    use cortex_m::singleton;
-    use panic_halt as _;
     use stm32f1xx_hal::{dma, gpio, pac, prelude::*, serial, timer};
     use systick_monotonic::Systick;
 
@@ -17,7 +17,10 @@ mod app {
     type MyMono = Systick<100>; // 100 Hz / 10 ms granularity
 
     #[shared]
-    struct Shared {}
+    struct Shared {
+        #[lock_free]
+        buffer: [u8; 256],
+    }
 
     #[local]
     struct Local {
@@ -54,12 +57,12 @@ mod app {
         let dma1 = cx.device.DMA1.split();
 
         // Serial config
-        let tx = gpioa.pa9.into_alternate_push_pull(&mut gpioa.crh);
-        let rx = gpioa.pa10; //.into_pull_up_input(&mut gpioa.crh);
-
         let serial = serial::Serial::new(
             cx.device.USART1,
-            (tx, rx),
+            (
+                gpioa.pa9.into_alternate_push_pull(&mut gpioa.crh),
+                gpioa.pa10, //.into_pull_up_input(&mut gpioa.crh),
+            ),
             &mut afio.mapr,
             serial::Config {
                 baudrate: 250_000.bps(),
@@ -69,7 +72,9 @@ mod app {
         );
 
         (
-            Shared {},
+            Shared {
+                buffer: [0b01010101; 256],
+            },
             Local {
                 tx: Some(serial.tx.with_dma(dma1.4)),
 
@@ -84,13 +89,12 @@ mod app {
         )
     }
 
-    #[idle(local = [tx, delay, led])]
+    #[idle(local = [tx, delay, led], shared = [&buffer])]
     fn idle(cx: idle::Context) -> ! {
-        let mut buf = singleton!(: [u8; 256] = [0b01010101; 256]).unwrap();
         let mut tx = cx.local.tx.take().unwrap();
 
         loop {
-            let xfer = tx.write(buf);
+            let xfer = tx.write(cx.shared.buffer);
 
             cx.local.delay.delay(1.secs());
             cx.local.led.set_high();
@@ -98,7 +102,7 @@ mod app {
             cx.local.delay.delay(1.secs());
             cx.local.led.set_low();
 
-            (buf, tx) = xfer.wait();
+            (_, tx) = xfer.wait();
         }
     }
 }