1 files changed, 49 insertions, 0 deletions
diff --git a/stm/pendsv.c b/stm/pendsv.c
new file mode 100644
index 0000000000..e8e5b840c6
--- /dev/null
+++ b/stm/pendsv.c
@@ -0,0 +1,49 @@
+#include <stdlib.h>
+#include <stm32f4xx.h>
+
+#include "misc.h"
+#include "mpconfig.h"
+#include "qstr.h"
+#include "obj.h"
+#include "pendsv.h"
+
+static mp_obj_t pendsv_object = MP_OBJ_NULL;
+
+void pendsv_init(void) {
+    // set PendSV interrupt at lowest priority
+    NVIC_SetPriority(PendSV_IRQn, 0xff);
+}
+
+// call this function to raise a pending exception during an interrupt
+// it will wait until all interrupts are finished then raise the given
+// exception object using nlr_jump in the context of the top-level thread
+void pendsv_nlr_jump(mp_obj_t o) {
+    pendsv_object = o;
+    SCB->ICSR = SCB_ICSR_PENDSVSET_Msk;
+}
+
+void pendsv_isr_handler(void) {
+    // re-jig the stack so that when we return from this interrupt handler
+    // it returns instead to nlr_jump with argument pendsv_object
+    __asm volatile (
+        "ldr r0, pendsv_object_ptr\n"
+        "ldr r0, [r0]\n"
+        "str r0, [sp, #0]\n"
+        "ldr r0, nlr_jump_ptr\n"
+        "str r0, [sp, #24]\n"
+        "bx lr\n"
+        ".align 2\n"
+        "pendsv_object_ptr: .word pendsv_object\n"
+        "nlr_jump_ptr: .word nlr_jump\n"
+    );
+
+    /*
+    sp[0] = r0 = exception to raise
+    sp[6] = pc = nlr_jump
+    uint32_t x[2] = {0x424242, 0xdeaddead};
+    printf("PendSV: %p\n", x);
+    for (uint32_t *p = (uint32_t*)(((uint32_t)x - 15) & 0xfffffff0), i = 64; i > 0; p += 4, i -= 4) {
+        printf(" %p: %08x %08x %08x %08x\n", p, p[0], p[1], p[2], p[3]);
+    }
+    */
+}