1 files changed, 83 insertions, 0 deletions
diff --git a/stmhal/pendsv.c b/stmhal/pendsv.c
new file mode 100644
index 0000000000..706f9011ff
--- /dev/null
+++ b/stmhal/pendsv.c
@@ -0,0 +1,83 @@
+#include <stdlib.h>
+#include <stm32f4xx_hal.h>
+
+#include "misc.h"
+#include "mpconfig.h"
+#include "qstr.h"
+#include "obj.h"
+#include "pendsv.h"
+
+static void *pendsv_object = NULL;
+
+void pendsv_init(void) {
+    // set PendSV interrupt at lowest priority
+    HAL_NVIC_SetPriority(PendSV_IRQn, 0xf, 0xf);
+}
+
+// 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(void *o) {
+    pendsv_object = o;
+    SCB->ICSR = SCB_ICSR_PENDSVSET_Msk;
+}
+
+// since we play tricks with the stack, the compiler must not generate a
+// prelude for this function
+void pendsv_isr_handler(void) __attribute__((naked));
+
+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
+    // note that stack has a different layout if DEBUG is enabled
+    //
+    // on entry to this (naked) function, stack has the following layout:
+    //
+    // stack layout with DEBUG disabled:
+    //   sp[6]: pc
+    //   sp[5]: ?
+    //   sp[4]: ?
+    //   sp[3]: ?
+    //   sp[2]: ?
+    //   sp[1]: ?
+    //   sp[0]: r0
+    //
+    // stack layout with DEBUG enabled:
+    //   sp[8]: pc
+    //   sp[7]: lr
+    //   sp[6]: ?
+    //   sp[5]: ?
+    //   sp[4]: ?
+    //   sp[3]: ?
+    //   sp[2]: r0
+    //   sp[1]: 0xfffffff9
+    //   sp[0]: ?
+
+    __asm volatile (
+        "ldr r0, pendsv_object_ptr\n"
+        "ldr r0, [r0]\n"
+#if defined(PENDSV_DEBUG)
+        "str r0, [sp, #8]\n"
+#else
+        "str r0, [sp, #0]\n"
+#endif
+        "ldr r0, nlr_jump_ptr\n"
+#if defined(PENDSV_DEBUG)
+        "str r0, [sp, #32]\n"
+#else
+        "str r0, [sp, #24]\n"
+#endif
+        "bx lr\n"
+        ".align 2\n"
+        "pendsv_object_ptr: .word pendsv_object\n"
+        "nlr_jump_ptr: .word nlr_jump\n"
+    );
+
+    /*
+    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, (uint)p[0], (uint)p[1], (uint)p[2], (uint)p[3]);
+    }
+    */
+}