4 files changed, 9 insertions, 0 deletions
diff --git a/ecdsa.c b/ecdsa.c
index 28cfa02..d1b8d0c 100644
--- a/ecdsa.c
+++ b/ecdsa.c
@@ -707,6 +707,7 @@ static hal_error_t point_scalar_multiply(const fp_int * const k,
     point_double (M[1],        M[1],    curve);
     point_add    (M[bit],  P,  M[bit],  curve);
 
+    hal_task_yield_maybe();
   }
 
   /*
diff --git a/hal_internal.h b/hal_internal.h
index 95785ae..b698611 100644
--- a/hal_internal.h
+++ b/hal_internal.h
@@ -153,6 +153,7 @@ extern void hal_critical_section_end(void);
 extern void hal_ks_lock(void);
 extern void hal_ks_unlock(void);
 extern void hal_task_yield(void);
+extern void hal_task_yield_maybe(void);
 
 /*
  * Thread sleep.  Currently used only for bad-PIN delays.
diff --git a/locks.c b/locks.c
index 9b81769..72af43b 100644
--- a/locks.c
+++ b/locks.c
@@ -106,6 +106,11 @@ WEAK_FUNCTION void hal_task_yield(void)
   return;
 }
 
+WEAK_FUNCTION void hal_task_yield_maybe(void)
+{
+  return;
+}
+
 /*
  * Local variables:
  * indent-tabs-mode: nil
diff --git a/pbkdf2.c b/pbkdf2.c
index 0a1e57e..87ff574 100644
--- a/pbkdf2.c
+++ b/pbkdf2.c
@@ -140,6 +140,8 @@ hal_error_t hal_pbkdf2(hal_core_t *core,
 
     for (iteration = 2; iteration <= iterations_desired; iteration++) {
 
+      hal_task_yield_maybe();
+
       if ((err = do_hmac(core, descriptor, password, password_length,
                          mac, descriptor->digest_length,
                          0, mac, sizeof(mac))) != HAL_OK)