From f5de8307b24bc6e8ce0190c73ebf6ae423d0c9ac Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <jorge@japaric.io>
Date: Wed, 1 May 2019 23:32:22 +0200
Subject: [PATCH] unlock the DWT, if locked, when using the timer queue

---
 macros/src/codegen.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/macros/src/codegen.rs b/macros/src/codegen.rs
index 4468216f53..d5bd3b4229 100644
--- a/macros/src/codegen.rs
+++ b/macros/src/codegen.rs
@@ -2024,6 +2024,15 @@ fn pre_init(ctxt: &Context, app: &App, analysis: &Analysis) -> proc_macro2::Toke
 
     // Set the cycle count to 0 and disable it while `init` executes
     if cfg!(feature = "timer-queue") {
+        exprs.push(quote!(
+            // unlock the DWT, if software locked
+            // See ARM CoreSight Architecture Specification v3.0, section B2.3.10
+            // 1 << 0 = Software lock mechanism is implemented.
+            // 1 << 1 = Writing to the other registers in the component is blocked
+            if p.DWT.lsr.read() & 0b11 == 0b11 {
+                p.DWT.lar.write(0xC5ACCE55);
+            }
+        ));
         exprs.push(quote!(p.DWT.ctrl.modify(|r| r & !1);));
         exprs.push(quote!(p.DWT.cyccnt.write(0);));
     }