From 109249913bfe9e04c881b1216c8c258d7b097c44 Mon Sep 17 00:00:00 2001
From: Matt Knight <mattnite@proton.me>
Date: Sun, 16 Apr 2023 12:47:52 -0700
Subject: [PATCH] check if the thread of execution is in an ISR on Cortex M
 (#123)

---
 src/modules/cpus/cortex-m.zig | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/modules/cpus/cortex-m.zig b/src/modules/cpus/cortex-m.zig
index f69151b..5b9715f 100644
--- a/src/modules/cpus/cortex-m.zig
+++ b/src/modules/cpus/cortex-m.zig
@@ -1,7 +1,32 @@
 const std = @import("std");
 const microzig = @import("microzig");
+const mmio = microzig.mmio;
 const root = @import("root");
 
+pub const regs = struct {
+    // Interrupt Control and State Register
+    pub const ICSR = @intToPtr(*volatile mmio.Mmio(packed struct {
+        VECTACTIVE: u9,
+        reserved0: u2,
+        RETTOBASE: u1,
+        VECTPENDING: u9,
+        reserved1: u1,
+        ISRPENDING: u1,
+        ISRPREEMPT: u1,
+        reserved2: u1,
+        PENDSTCLR: u1,
+        PENDSTSET: u1,
+        PENDSVCLR: u1,
+        PENDSVSET: u1,
+        reserved3: u2,
+        NMIPENDSET: u1,
+    }), 0xE000ED04);
+};
+
+pub fn executing_isr() bool {
+    return regs.ICSR.read().VECTACTIVE != 0;
+}
+
 pub fn sei() void {
     asm volatile ("cpsie i");
 }