async: Add preliminary time scheduler.

1 files changed, 21 insertions, 0 deletions

diff --git a/cortex_m/critical_section.h b/cortex_m/critical_section.h
new file mode 100644
index 0000000..6b611a8
--- /dev/null
+++ b/cortex_m/critical_section.h
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <cstdint>
+
+struct critical_section {
+    uint32_t primask;
+
+    critical_section() {
+        asm volatile("mrs %0, primask" : "=r" (primask));
+
+        asm volatile("cpsid i");
+
+        asm volatile("dmb");
+    }
+
+    ~critical_section() {
+        asm volatile("dmb");
+
+        asm volatile("msr primask, %0" :: "r" (primask));
+    }
+};