From e990021b9a9d3acc309c21bd4ddf3ff090bb7999 Mon Sep 17 00:00:00 2001
From: Ulf Lilleengen <ulf.lilleengen@gmail.com>
Date: Wed, 9 Feb 2022 12:46:46 +0100
Subject: [PATCH] Address review comments

---
 embassy-boot/nrf/src/lib.rs  | 7 +++++++
 embassy-boot/nrf/src/main.rs | 5 ++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/embassy-boot/nrf/src/lib.rs b/embassy-boot/nrf/src/lib.rs
index af7ec7da2..32250b2db 100644
--- a/embassy-boot/nrf/src/lib.rs
+++ b/embassy-boot/nrf/src/lib.rs
@@ -100,6 +100,13 @@ impl BootLoader {
 
         trace!("msp = {=u32:x}, rv = {=u32:x}", msp, rv);
 
+        // These instructions perform the following operations:
+        //
+        // * Modify control register to use MSP as stack pointer (clear spsel bit)
+        // * Synchronize instruction barrier
+        // * Initialize stack pointer (0x1000)
+        // * Set link register to not return (0xFF)
+        // * Jump to softdevice reset vector
         core::arch::asm!(
             "mrs {tmp}, CONTROL",
             "bics {tmp}, {spsel}",
diff --git a/embassy-boot/nrf/src/main.rs b/embassy-boot/nrf/src/main.rs
index 08b854a7e..cd264d4c2 100644
--- a/embassy-boot/nrf/src/main.rs
+++ b/embassy-boot/nrf/src/main.rs
@@ -12,6 +12,9 @@ use embassy_nrf::nvmc::Nvmc;
 #[entry]
 fn main() -> ! {
     let p = embassy_nrf::init(Default::default());
+
+    // Uncomment this if you are debugging the bootloader with debugger/RTT attached,
+    // as it prevents a hard fault when accessing flash 'too early' after boot.
     /*
         for i in 0..10000000 {
             cortex_m::asm::nop();
@@ -40,7 +43,7 @@ unsafe fn DefaultHandler(_: i16) -> ! {
 #[panic_handler]
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     unsafe {
-        core::arch::asm!("udf #0");
+        cortex_m::asm::udf();
         core::hint::unreachable_unchecked();
     }
 }