1 files changed, 40 insertions, 17 deletions

diff --git a/examples/nrf/src/bin/saadc_continuous.rs b/examples/nrf/src/bin/saadc_continuous.rs
index 81559237b..991adabad 100644
--- a/examples/nrf/src/bin/saadc_continuous.rs
+++ b/examples/nrf/src/bin/saadc_continuous.rs
@@ -5,6 +5,7 @@
 #[path = "../example_common.rs"]
 mod example_common;
 use embassy::executor::Spawner;
+use embassy::time::Duration;
 use embassy_nrf::ppi::Ppi;
 use embassy_nrf::saadc::{ChannelConfig, Config, Saadc, SamplerState};
 use embassy_nrf::timer::{Frequency, Timer};
@@ -26,34 +27,56 @@ async fn main(_spawner: Spawner, mut p: Peripherals) {
         [channel_1_config, channel_2_config, channel_3_config],
     );
 
+    // We want the task start to effectively short with the last one ending so
+    // we don't miss any samples. The Saadc will trigger the initial TASKS_START.
+    let mut start_ppi = Ppi::new_one_to_one(p.PPI_CH0, saadc.event_end(), saadc.task_start());
+    start_ppi.enable();
+
     let mut timer = Timer::new(p.TIMER0);
     timer.set_frequency(Frequency::F1MHz);
-    timer.cc(0).write(100); // We want to sample at 10KHz
+    timer.cc(0).write(1000); // We want to sample at 1KHz
     timer.cc(0).short_compare_clear();
 
-    let mut ppi = Ppi::new_one_to_one(p.PPI_CH0, timer.cc(0).event_compare(), saadc.task_sample());
-    ppi.enable();
+    let mut sample_ppi =
+        Ppi::new_one_to_one(p.PPI_CH1, timer.cc(0).event_compare(), saadc.task_sample());
 
     timer.start();
 
-    let mut bufs = [[[0; 3]; 50]; 2];
+    // This delay demonstrates that starting the timer prior to running
+    // the task sampler is benign given the calibration that follows.
+    embassy::time::Timer::after(Duration::from_millis(500)).await;
+    saadc.calibrate().await;
+
+    let mut bufs = [[[0; 3]; 500]; 2];
 
     let mut c = 0;
     let mut a: i32 = 0;
 
     saadc
-        .run_task_sampler(&mut bufs, move |buf| {
-            for b in buf {
-                a += b[0] as i32;
-            }
-            c += buf.len();
-            if c > 10000 {
-                a = a / c as i32;
-                info!("channel 1: {=i32}", a);
-                c = 0;
-                a = 0;
-            }
-            SamplerState::Sampled
-        })
+        .run_task_sampler(
+            &mut bufs,
+            || {
+                sample_ppi.enable();
+            },
+            move |buf| {
+                // NOTE: It is important that the time spent within this callback
+                // does not exceed the time taken to acquire the 1500 samples we
+                // have in this example, which would be 10us + 2us per
+                // sample * 1500 = 18ms. You need to measure the time taken here
+                // and set the sample buffer size accordingly. Exceeding this
+                // time can lead to the peripheral re-writing the other buffer.
+                for b in buf {
+                    a += b[0] as i32;
+                }
+                c += buf.len();
+                if c > 1000 {
+                    a = a / c as i32;
+                    info!("channel 1: {=i32}", a);
+                    c = 0;
+                    a = 0;
+                }
+                SamplerState::Sampled
+            },
+        )
         .await;
 }