diff --git a/Makefile b/Makefile
index 2e7946e..b7f98db 100644
--- a/Makefile
+++ b/Makefile
@@ -184,10 +184,11 @@ $(VENDOR_SDK_DIR_1.5.4)/.dir: $(VENDOR_SDK_ZIP_1.5.4)
 
 sdk_patch: $(VENDOR_SDK_DIR)/.dir .sdk_patch_$(VENDOR_SDK)
 
-.sdk_patch_2.0.0:
+.sdk_patch_2.0.0: user_rf_cal_sector_set.o
 	echo -e "#undef ESP_SDK_VERSION\n#define ESP_SDK_VERSION 020000" >>$(VENDOR_SDK_DIR)/include/esp_sdk_ver.h
 	$(PATCH) -d $(VENDOR_SDK_DIR) -p1 < c_types-c99_sdk_2.patch
 	cd $(VENDOR_SDK_DIR)/lib; mkdir -p tmp; cd tmp; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar x ../libcrypto.a; cd ..; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar rs libwpa.a tmp/*.o
+	$(TOOLCHAIN)/bin/xtensa-lx106-elf-ar r $(VENDOR_SDK_DIR)/lib/libmain.a user_rf_cal_sector_set.o
 	@touch $@
 
 .sdk_patch_1.5.4:
@@ -320,6 +321,9 @@ sdk_patch: $(VENDOR_SDK_DIR)/.dir .sdk_patch_$(VENDOR_SDK)
 empty_user_rf_pre_init.o: empty_user_rf_pre_init.c $(TOOLCHAIN)/bin/xtensa-lx106-elf-gcc
 	$(TOOLCHAIN)/bin/xtensa-lx106-elf-gcc -O2 -c $<
 
+user_rf_cal_sector_set.o: user_rf_cal_sector_set.c $(TOOLCHAIN)/bin/xtensa-lx106-elf-gcc
+	$(TOOLCHAIN)/bin/xtensa-lx106-elf-gcc -O2 -c $<
+
 lwip: toolchain sdk_patch
 ifeq ($(STANDALONE),y)
 	make -C esp-open-lwip -f Makefile.open install \
diff --git a/user_rf_cal_sector_set.c b/user_rf_cal_sector_set.c
new file mode 100644
index 0000000..0dc4fd3
--- /dev/null
+++ b/user_rf_cal_sector_set.c
@@ -0,0 +1,11 @@
+#include <c_types.h>
+#include <spi_flash.h>
+
+uint32 user_rf_cal_sector_set(void) {
+    extern char flashchip;
+    SpiFlashChip *flash = (SpiFlashChip*)(&flashchip + 4);
+    // We know that sector size in 4096
+    //uint32_t sec_num = flash->chip_size / flash->sector_size;
+    uint32_t sec_num = flash->chip_size >> 12;
+    return sec_num - 5;
+}