From 8402c26cfa98b4689f5ac4673952a654cfe5b678 Mon Sep 17 00:00:00 2001
From: Damien George <damien.p.george@gmail.com>
Date: Thu, 18 Apr 2019 17:15:11 +1000
Subject: [PATCH] stm32/powerctrl: Enable EIWUP to ensure RTC wakes device from
 standby.

---
 ports/stm32/powerctrl.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/ports/stm32/powerctrl.c b/ports/stm32/powerctrl.c
index 165919977..669e568f8 100644
--- a/ports/stm32/powerctrl.c
+++ b/ports/stm32/powerctrl.c
@@ -390,6 +390,12 @@ void powerctrl_enter_standby_mode(void) {
     // enable previously-enabled RTC interrupts
     RTC->CR |= save_irq_bits;
 
+    #if defined(STM32F7)
+    // Enable the internal (eg RTC) wakeup sources
+    // See Errata 2.2.2 "Wakeup from Standby mode when the back-up SRAM regulator is enabled"
+    PWR->CSR1 |= PWR_CSR1_EIWUP;
+    #endif
+
     // enter standby mode
     HAL_PWR_EnterSTANDBYMode();
     // we never return; MCU is reset on exit from standby