feat(u3): deepSleep

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

src/low_power.c

@@ -495,14 +495,14 @@ void LowPower_stop(serial_t *obj)
     // STM32L4+ must keep SRAM3 content when entering STOP2 lowpower mode
     HAL_PWREx_EnableSRAM3ContentRetention();
 #endif /* PWR_CR1_RRSTP */
-    // STM32L4xx and STM32H7xx supports STOP2 mode which halves consumption
 #if defined(STM32H7xx)
 #if defined(PWR_LOWPOWERREGULATOR_ON)
     HAL_PWREx_EnterSTOP2Mode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
 #else
     HAL_PWREx_EnterSTOP2Mode(PWR_MAINREGULATOR_ON, PWR_STOPENTRY_WFI);
 #endif
-    HAL_PWREx_EnterSTOP2Mode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
+#elif defined(STM32U3xx)
+    HAL_PWR_EnterSTOPMode(PWR_LOWPOWERMODE_STOP2, PWR_STOPENTRY_WFI);
 #else
     HAL_PWREx_EnterSTOP2Mode(PWR_STOPENTRY_WFI);
 #endif