deep sleep: keep RTC_SLOW_MEM powered on if data is placed into RTC slow memory

components/esp32/deep_sleep.c

@@ -302,12 +302,18 @@ static uint32_t get_power_down_flags()
 {
     // Where needed, convert AUTO options to ON. Later interpret AUTO as OFF.
 
-    // RTC_SLOW_MEM is needed only for the ULP.
-    // If RTC_SLOW_MEM is Auto, and ULP wakeup isn't enabled, power down RTC_SLOW_MEM.
-    if (s_config.pd_options[ESP_PD_DOMAIN_RTC_SLOW_MEM] == ESP_PD_OPTION_AUTO) {
-        if (s_config.wakeup_triggers & RTC_SAR_TRIG_EN) {
-            s_config.pd_options[ESP_PD_DOMAIN_RTC_SLOW_MEM] = ESP_PD_OPTION_ON;
-        }
+    // RTC_SLOW_MEM is needed for the ULP, so keep RTC_SLOW_MEM powered up if ULP
+    // is used and RTC_SLOW_MEM is Auto.
+    // If there is any data placed into .rtc.data or .rtc.bss segments, and
+    // RTC_SLOW_MEM is Auto, keep it powered up as well.
+
+    // These labels are defined in the linker script:
+    extern int _rtc_data_start, _rtc_data_end, _rtc_bss_start, _rtc_bss_end;
+
+    if (s_config.pd_options[ESP_PD_DOMAIN_RTC_SLOW_MEM] == ESP_PD_OPTION_AUTO ||
+            &_rtc_data_end > &_rtc_data_start ||
+            &_rtc_bss_end > &_rtc_bss_start) {
+        s_config.pd_options[ESP_PD_DOMAIN_RTC_SLOW_MEM] = ESP_PD_OPTION_ON;
     }
 
     // RTC_FAST_MEM is needed for deep sleep stub.

components/esp32/include/esp_attr.h

@@ -26,7 +26,7 @@
 // Forces data into DRAM instead of flash
 #define DRAM_ATTR __attribute__((section(".dram1")))
 
-// Forces a string into DRAM instrad of flash
+// Forces a string into DRAM instead of flash
 // Use as ets_printf(DRAM_STR("Hello world!\n"));
 #define DRAM_STR(str) (__extension__({static const DRAM_ATTR char __c[] = (str); (const char *)&__c;}))
 

components/esp32/ld/esp32.common.ld

@@ -19,9 +19,11 @@ SECTIONS
   */
   .rtc.data :
   {
+    _rtc_data_start = ABSOLUTE(.);
     *(.rtc.data)
     *(.rtc.rodata)
     *rtc_wake_stub*.o(.data .rodata .data.* .rodata.* .bss .bss.*)
+    _rtc_data_end = ABSOLUTE(.);
   } > rtc_slow_seg
 
   /* RTC bss, from any source file named rtc_wake_stub*.c */

docs/api/deep_sleep.rst

@@ -73,6 +73,8 @@ By default, ``esp_deep_sleep_start`` function will power down all RTC power doma
 
 Note: on the first revision of the ESP32, RTC fast memory will always be kept enabled in deep sleep, so that the deep sleep stub can run after reset. This can be overriden, if the application doesn't need clean reset behaviour after deep sleep.
 
+If some variables in the program are placed into RTC slow memory (for example, using ``RTC_DATA_ATTR`` attribute), RTC slow memory will be kept powered on by default. This can be overriden using ``esp_deep_sleep_pd_config`` function, if desired.
+
 .. doxygenfunction:: esp_deep_sleep_pd_config
 .. doxygenenum:: esp_deep_sleep_pd_domain_t
 .. doxygenenum:: esp_deep_sleep_pd_option_t