added hacked poke example to interrupts chapter; *do not use*

Author: BartMassey

mdbook/src/15-interrupts/examples/poke-hacked.rs

@@ -0,0 +1,71 @@
+#![no_main]
+#![no_std]
+
+use cortex_m::asm;
+use cortex_m_rt::entry;
+use panic_rtt_target as _;
+use rtt_target::{rprintln, rtt_init_print};
+
+use microbit::{
+    Board,
+    hal::{
+        gpiote,
+        pac::{self, interrupt},
+    },
+};
+
+static mut GPIOTE_PERIPHERAL: Option<gpiote::Gpiote> = None;
+
+/// This "function" will be called when an interrupt is
+/// received. For now, just report and panic.
+#[interrupt]
+fn GPIOTE() {
+    rprintln!("ouch");
+    // # Safety
+    // Ideally, this ISR cannot be called until the global
+    // has been properly initialized. This value is never
+    // touched globally after that.
+    unsafe {
+        if let Some(ref mut gpiote) = GPIOTE_PERIPHERAL {
+            let channel = gpiote.channel0();
+            channel.reset_events();
+            // panic!();
+        }
+    }
+}
+
+#[entry]
+fn main() -> ! {
+    rtt_init_print!();
+
+    let board = Board::take().unwrap();
+    let button_a = board.buttons.button_a.into_floating_input();
+    let gpiote = gpiote::Gpiote::new(board.GPIOTE);
+
+    // Set up the GPIOTE to generate an interrupt when Button A is pressed (GPIO
+    // wire goes low).
+    let channel = gpiote.channel0();
+    channel
+        .input_pin(&button_a.degrade())
+        .hi_to_lo()
+        .enable_interrupt();
+    channel.reset_events();
+    // # Safety
+    // GPIOTE cannot be used from interrupt handler yet,
+    // since it's not turned on. (I think this is bogus; the
+    // write is not guaranteed to complete before the end of
+    // the function maybe? An `UnsafeCell` is probably needed
+    // here, at bare minimum.)
+    unsafe { GPIOTE_PERIPHERAL = Some(gpiote) };
+
+    // Set up the NVIC to handle GPIO interrupts.
+    // # Safety
+    // Interrupt handler is set up properly.
+    unsafe { pac::NVIC::unmask(pac::Interrupt::GPIOTE) };
+    pac::NVIC::unpend(pac::Interrupt::GPIOTE);
+
+    loop {
+        // "wait for interrupt": CPU goes to sleep until an interrupt.
+        asm::wfi();
+    }
+}