What I didn't mention is that I also plan to use GPIO15 and 16 for the 32kHz crystal.
I was not able to use GPIO17 as RTC because it's not a TOUCHPAD GPIO, and thus I could not find which registers could control it (from the wake stub). But I have finally found a way thanks to the array below declared in esp/v5.1.4/esp-idf/components/soc/esp32s3/rtc_io_periph.c (I share it below in case it would save hours of research to others).
[ But still, I am interested in finding a proper way to power the outputs without having this reset in the wake stub - as VBAT does not help unfortunately. ]
//Reg,Mux,Fun,IE,Up,Down,Rtc_number
const rtc_io_desc_t rtc_io_desc[SOC_RTCIO_PIN_COUNT] = {
/*REG MUX select function select Input enable Pullup Pulldown Sleep select Sleep input enable Sleep output enable PAD hold Pad force hold Mask of drive capability Offset gpio number */
{RTC_IO_TOUCH_PAD0_REG, RTC_IO_TOUCH_PAD0_MUX_SEL_M, RTC_IO_TOUCH_PAD0_FUN_SEL_S, RTC_IO_TOUCH_PAD0_FUN_IE_M, RTC_IO_TOUCH_PAD0_RUE_M, RTC_IO_TOUCH_PAD0_RDE_M, RTC_IO_TOUCH_PAD0_SLP_SEL_M, RTC_IO_TOUCH_PAD0_SLP_IE_M, RTC_IO_TOUCH_PAD0_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD0_HOLD_M, RTC_IO_TOUCH_PAD0_DRV_V, RTC_IO_TOUCH_PAD0_DRV_S, RTCIO_CHANNEL_0_GPIO_NUM}, //0
{RTC_IO_TOUCH_PAD1_REG, RTC_IO_TOUCH_PAD1_MUX_SEL_M, RTC_IO_TOUCH_PAD1_FUN_SEL_S, RTC_IO_TOUCH_PAD1_FUN_IE_M, RTC_IO_TOUCH_PAD1_RUE_M, RTC_IO_TOUCH_PAD1_RDE_M, RTC_IO_TOUCH_PAD1_SLP_SEL_M, RTC_IO_TOUCH_PAD1_SLP_IE_M, RTC_IO_TOUCH_PAD1_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD1_HOLD_M, RTC_IO_TOUCH_PAD1_DRV_V, RTC_IO_TOUCH_PAD1_DRV_S, RTCIO_CHANNEL_1_GPIO_NUM}, //1
{RTC_IO_TOUCH_PAD2_REG, RTC_IO_TOUCH_PAD2_MUX_SEL_M, RTC_IO_TOUCH_PAD2_FUN_SEL_S, RTC_IO_TOUCH_PAD2_FUN_IE_M, RTC_IO_TOUCH_PAD2_RUE_M, RTC_IO_TOUCH_PAD2_RDE_M, RTC_IO_TOUCH_PAD2_SLP_SEL_M, RTC_IO_TOUCH_PAD2_SLP_IE_M, RTC_IO_TOUCH_PAD2_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD2_HOLD_M, RTC_IO_TOUCH_PAD2_DRV_V, RTC_IO_TOUCH_PAD2_DRV_S, RTCIO_CHANNEL_2_GPIO_NUM}, //2
{RTC_IO_TOUCH_PAD3_REG, RTC_IO_TOUCH_PAD3_MUX_SEL_M, RTC_IO_TOUCH_PAD3_FUN_SEL_S, RTC_IO_TOUCH_PAD3_FUN_IE_M, RTC_IO_TOUCH_PAD3_RUE_M, RTC_IO_TOUCH_PAD3_RDE_M, RTC_IO_TOUCH_PAD3_SLP_SEL_M, RTC_IO_TOUCH_PAD3_SLP_IE_M, RTC_IO_TOUCH_PAD3_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD3_HOLD_M, RTC_IO_TOUCH_PAD3_DRV_V, RTC_IO_TOUCH_PAD3_DRV_S, RTCIO_CHANNEL_3_GPIO_NUM}, //3
{RTC_IO_TOUCH_PAD4_REG, RTC_IO_TOUCH_PAD4_MUX_SEL_M, RTC_IO_TOUCH_PAD4_FUN_SEL_S, RTC_IO_TOUCH_PAD4_FUN_IE_M, RTC_IO_TOUCH_PAD4_RUE_M, RTC_IO_TOUCH_PAD4_RDE_M, RTC_IO_TOUCH_PAD4_SLP_SEL_M, RTC_IO_TOUCH_PAD4_SLP_IE_M, RTC_IO_TOUCH_PAD4_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD4_HOLD_M, RTC_IO_TOUCH_PAD4_DRV_V, RTC_IO_TOUCH_PAD4_DRV_S, RTCIO_CHANNEL_4_GPIO_NUM}, //4
{RTC_IO_TOUCH_PAD5_REG, RTC_IO_TOUCH_PAD5_MUX_SEL_M, RTC_IO_TOUCH_PAD5_FUN_SEL_S, RTC_IO_TOUCH_PAD5_FUN_IE_M, RTC_IO_TOUCH_PAD5_RUE_M, RTC_IO_TOUCH_PAD5_RDE_M, RTC_IO_TOUCH_PAD5_SLP_SEL_M, RTC_IO_TOUCH_PAD5_SLP_IE_M, RTC_IO_TOUCH_PAD5_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD5_HOLD_M, RTC_IO_TOUCH_PAD5_DRV_V, RTC_IO_TOUCH_PAD5_DRV_S, RTCIO_CHANNEL_5_GPIO_NUM}, //5
{RTC_IO_TOUCH_PAD6_REG, RTC_IO_TOUCH_PAD6_MUX_SEL_M, RTC_IO_TOUCH_PAD6_FUN_SEL_S, RTC_IO_TOUCH_PAD6_FUN_IE_M, RTC_IO_TOUCH_PAD6_RUE_M, RTC_IO_TOUCH_PAD6_RDE_M, RTC_IO_TOUCH_PAD6_SLP_SEL_M, RTC_IO_TOUCH_PAD6_SLP_IE_M, RTC_IO_TOUCH_PAD6_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD6_HOLD_M, RTC_IO_TOUCH_PAD6_DRV_V, RTC_IO_TOUCH_PAD6_DRV_S, RTCIO_CHANNEL_6_GPIO_NUM}, //6
{RTC_IO_TOUCH_PAD7_REG, RTC_IO_TOUCH_PAD7_MUX_SEL_M, RTC_IO_TOUCH_PAD7_FUN_SEL_S, RTC_IO_TOUCH_PAD7_FUN_IE_M, RTC_IO_TOUCH_PAD7_RUE_M, RTC_IO_TOUCH_PAD7_RDE_M, RTC_IO_TOUCH_PAD7_SLP_SEL_M, RTC_IO_TOUCH_PAD7_SLP_IE_M, RTC_IO_TOUCH_PAD7_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD7_HOLD_M, RTC_IO_TOUCH_PAD7_DRV_V, RTC_IO_TOUCH_PAD7_DRV_S, RTCIO_CHANNEL_7_GPIO_NUM}, //7
{RTC_IO_TOUCH_PAD8_REG, RTC_IO_TOUCH_PAD8_MUX_SEL_M, RTC_IO_TOUCH_PAD8_FUN_SEL_S, RTC_IO_TOUCH_PAD8_FUN_IE_M, RTC_IO_TOUCH_PAD8_RUE_M, RTC_IO_TOUCH_PAD8_RDE_M, RTC_IO_TOUCH_PAD8_SLP_SEL_M, RTC_IO_TOUCH_PAD8_SLP_IE_M, RTC_IO_TOUCH_PAD8_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD8_HOLD_M, RTC_IO_TOUCH_PAD8_DRV_V, RTC_IO_TOUCH_PAD8_DRV_S, RTCIO_CHANNEL_8_GPIO_NUM}, //8
{RTC_IO_TOUCH_PAD9_REG, RTC_IO_TOUCH_PAD9_MUX_SEL_M, RTC_IO_TOUCH_PAD9_FUN_SEL_S, RTC_IO_TOUCH_PAD9_FUN_IE_M, RTC_IO_TOUCH_PAD9_RUE_M, RTC_IO_TOUCH_PAD9_RDE_M, RTC_IO_TOUCH_PAD9_SLP_SEL_M, RTC_IO_TOUCH_PAD9_SLP_IE_M, RTC_IO_TOUCH_PAD9_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD9_HOLD_M, RTC_IO_TOUCH_PAD9_DRV_V, RTC_IO_TOUCH_PAD9_DRV_S, RTCIO_CHANNEL_9_GPIO_NUM}, //9
{RTC_IO_TOUCH_PAD10_REG, RTC_IO_TOUCH_PAD10_MUX_SEL_M, RTC_IO_TOUCH_PAD10_FUN_SEL_S, RTC_IO_TOUCH_PAD10_FUN_IE_M, RTC_IO_TOUCH_PAD10_RUE_M, RTC_IO_TOUCH_PAD10_RDE_M, RTC_IO_TOUCH_PAD10_SLP_SEL_M, RTC_IO_TOUCH_PAD10_SLP_IE_M, RTC_IO_TOUCH_PAD10_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD10_HOLD_M, RTC_IO_TOUCH_PAD10_DRV_V, RTC_IO_TOUCH_PAD10_DRV_S, RTCIO_CHANNEL_10_GPIO_NUM}, //10
{RTC_IO_TOUCH_PAD11_REG, RTC_IO_TOUCH_PAD11_MUX_SEL_M, RTC_IO_TOUCH_PAD11_FUN_SEL_S, RTC_IO_TOUCH_PAD11_FUN_IE_M, RTC_IO_TOUCH_PAD11_RUE_M, RTC_IO_TOUCH_PAD11_RDE_M, RTC_IO_TOUCH_PAD11_SLP_SEL_M, RTC_IO_TOUCH_PAD11_SLP_IE_M, RTC_IO_TOUCH_PAD11_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD11_HOLD_M, RTC_IO_TOUCH_PAD11_DRV_V, RTC_IO_TOUCH_PAD11_DRV_S, RTCIO_CHANNEL_11_GPIO_NUM}, //11
{RTC_IO_TOUCH_PAD12_REG, RTC_IO_TOUCH_PAD12_MUX_SEL_M, RTC_IO_TOUCH_PAD12_FUN_SEL_S, RTC_IO_TOUCH_PAD12_FUN_IE_M, RTC_IO_TOUCH_PAD12_RUE_M, RTC_IO_TOUCH_PAD12_RDE_M, RTC_IO_TOUCH_PAD12_SLP_SEL_M, RTC_IO_TOUCH_PAD12_SLP_IE_M, RTC_IO_TOUCH_PAD12_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD12_HOLD_M, RTC_IO_TOUCH_PAD12_DRV_V, RTC_IO_TOUCH_PAD12_DRV_S, RTCIO_CHANNEL_12_GPIO_NUM}, //12
{RTC_IO_TOUCH_PAD13_REG, RTC_IO_TOUCH_PAD13_MUX_SEL_M, RTC_IO_TOUCH_PAD13_FUN_SEL_S, RTC_IO_TOUCH_PAD13_FUN_IE_M, RTC_IO_TOUCH_PAD13_RUE_M, RTC_IO_TOUCH_PAD13_RDE_M, RTC_IO_TOUCH_PAD13_SLP_SEL_M, RTC_IO_TOUCH_PAD13_SLP_IE_M, RTC_IO_TOUCH_PAD13_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD13_HOLD_M, RTC_IO_TOUCH_PAD13_DRV_V, RTC_IO_TOUCH_PAD13_DRV_S, RTCIO_CHANNEL_13_GPIO_NUM}, //13
{RTC_IO_TOUCH_PAD14_REG, RTC_IO_TOUCH_PAD14_MUX_SEL_M, RTC_IO_TOUCH_PAD14_FUN_SEL_S, RTC_IO_TOUCH_PAD14_FUN_IE_M, RTC_IO_TOUCH_PAD14_RUE_M, RTC_IO_TOUCH_PAD14_RDE_M, RTC_IO_TOUCH_PAD14_SLP_SEL_M, RTC_IO_TOUCH_PAD14_SLP_IE_M, RTC_IO_TOUCH_PAD14_SLP_OE_M, 0, RTC_CNTL_TOUCH_PAD14_HOLD_M, RTC_IO_TOUCH_PAD14_DRV_V, RTC_IO_TOUCH_PAD14_DRV_S, RTCIO_CHANNEL_14_GPIO_NUM}, //14
{RTC_IO_XTAL_32P_PAD_REG, RTC_IO_X32P_MUX_SEL_M, RTC_IO_X32P_FUN_SEL_S, RTC_IO_X32P_FUN_IE_M, RTC_IO_X32P_RUE_M, RTC_IO_X32P_RDE_M, RTC_IO_X32P_SLP_SEL_M, RTC_IO_X32P_SLP_IE_M, RTC_IO_X32P_SLP_OE_M, 0, RTC_CNTL_X32P_HOLD_M, RTC_IO_X32P_DRV_V, RTC_IO_X32P_DRV_S, RTCIO_CHANNEL_15_GPIO_NUM}, //15
{RTC_IO_XTAL_32N_PAD_REG, RTC_IO_X32N_MUX_SEL_M, RTC_IO_X32N_FUN_SEL_S, RTC_IO_X32N_FUN_IE_M, RTC_IO_X32N_RUE_M, RTC_IO_X32N_RDE_M, RTC_IO_X32N_SLP_SEL_M, RTC_IO_X32N_SLP_IE_M, RTC_IO_X32N_SLP_OE_M, 0, RTC_CNTL_X32N_HOLD_M, RTC_IO_X32N_DRV_V, RTC_IO_X32N_DRV_S, RTCIO_CHANNEL_16_GPIO_NUM}, //16
{RTC_IO_PAD_DAC1_REG, RTC_IO_PDAC1_MUX_SEL_M, RTC_IO_PDAC1_FUN_SEL_S, RTC_IO_PDAC1_FUN_IE_M, RTC_IO_PDAC1_RUE_M, RTC_IO_PDAC1_RDE_M, RTC_IO_PDAC1_SLP_SEL_M, RTC_IO_PDAC1_SLP_IE_M, RTC_IO_PDAC1_SLP_OE_M, 0, RTC_CNTL_PDAC1_HOLD_M, RTC_IO_PDAC1_DRV_V, RTC_IO_PDAC1_DRV_S, RTCIO_CHANNEL_17_GPIO_NUM}, //17
{RTC_IO_PAD_DAC2_REG, RTC_IO_PDAC2_MUX_SEL_M, RTC_IO_PDAC2_FUN_SEL_S, RTC_IO_PDAC2_FUN_IE_M, RTC_IO_PDAC2_RUE_M, RTC_IO_PDAC2_RDE_M, RTC_IO_PDAC2_SLP_SEL_M, RTC_IO_PDAC2_SLP_IE_M, RTC_IO_PDAC2_SLP_OE_M, 0, RTC_CNTL_PDAC2_HOLD_M, RTC_IO_PDAC2_DRV_V, RTC_IO_PDAC2_DRV_S, RTCIO_CHANNEL_18_GPIO_NUM}, //18
{RTC_IO_RTC_PAD19_REG, RTC_IO_PAD19_MUX_SEL_M, RTC_IO_PAD19_FUN_SEL_S, RTC_IO_PAD19_FUN_IE_M, RTC_IO_PAD19_RUE_M, RTC_IO_PAD19_RDE_M, RTC_IO_PAD19_SLP_SEL_M, RTC_IO_PAD19_SLP_IE_M, RTC_IO_PAD19_SLP_OE_M, 0, RTC_CNTL_PAD19_HOLD_M, RTC_IO_PAD19_DRV_V, RTC_IO_PAD19_DRV_S, RTCIO_CHANNEL_19_GPIO_NUM}, //19
{RTC_IO_RTC_PAD20_REG, RTC_IO_PAD20_MUX_SEL_M, RTC_IO_PAD20_FUN_SEL_S, RTC_IO_PAD20_FUN_IE_M, RTC_IO_PAD20_RUE_M, RTC_IO_PAD20_RDE_M, RTC_IO_PAD20_SLP_SEL_M, RTC_IO_PAD20_SLP_IE_M, RTC_IO_PAD20_SLP_OE_M, 0, RTC_CNTL_PAD20_HOLD_M, RTC_IO_PAD20_DRV_V, RTC_IO_PAD20_DRV_S, RTCIO_CHANNEL_20_GPIO_NUM}, //20
{RTC_IO_RTC_PAD21_REG, RTC_IO_PAD21_MUX_SEL_M, RTC_IO_PAD21_FUN_SEL_S, RTC_IO_PAD21_FUN_IE_M, RTC_IO_PAD21_RUE_M, RTC_IO_PAD21_RDE_M, RTC_IO_PAD21_SLP_SEL_M, RTC_IO_PAD21_SLP_IE_M, RTC_IO_PAD21_SLP_OE_M, 0, RTC_CNTL_PAD21_HOLD_M, RTC_IO_PAD21_DRV_V, RTC_IO_PAD21_DRV_S, RTCIO_CHANNEL_21_GPIO_NUM}, //21
};
This table is unfortunately not in RTC RAM, so I have created a clone in RTC RAM so that we can use it from the wake stub:
RTC_DATA_ATTR const rtc_io_desc_t my_rtc_io_desc[22] = {
...
Then, to set a pin "PIN" as RTC Output::
REG_WRITE(my_rtc_io_desc[PIN].reg, my_rtc_io_desc[PIN].mux);
SET_PERI_REG_MASK(SENS_SAR_PERI_CLK_GATE_CONF_REG, SENS_IOMUX_CLK_EN_M);
REG_WRITE(RTC_GPIO_ENABLE_W1TS_REG, BIT(RTC_GPIO_ENABLE_W1TS_S + PIN));
And to set PIN to value VAL:
if(VAL) {
REG_WRITE(RTC_GPIO_OUT_W1TS_REG, BIT(RTC_GPIO_OUT_DATA_W1TS_S + PIN));
}
else {
REG_WRITE(RTC_GPIO_OUT_W1TC_REG, BIT(RTC_GPIO_OUT_DATA_W1TC_S + PIN));
}
CLEAR_PERI_REG_MASK(RTC_CNTL_PAD_HOLD_REG, BIT(PIN));
SET_PERI_REG_MASK(RTC_CNTL_PAD_HOLD_REG, BIT(PIN));
