cpu/esp32: compile bootloader from ESP-IDF v4.4 source

cpu/esp32/bootloader/Kconfig

@@ -0,0 +1,14 @@
+# Copyright (c) 2022 Gunar Schorcht
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+#
+
+config MODULE_ESP_BOOTLOADER
+    bool
+    depends on TEST_KCONFIG
+    depends on HAS_ARCH_ESP32
+    default y
+    help
+        Bootloader compiled from ESP-IDF code.

cpu/esp32/bootloader/Makefile

@@ -0,0 +1,295 @@
+# Bootloader binary blob
+MODULE = esp_bootloader
+
+# We are compiling the bootloader from the ESP32 SDK sources, so we
+# can't use the automatic module SRC discovery rules. Also, the compiled code
+# would not be linked into the application, instead it is linked into its own
+# binary file.
+NO_AUTO_SRC = 1
+
+include $(RIOTBASE)/Makefile.base
+
+# Bootloader baudrate, set to the application defined one if any or the default
+# in serial.inc.mk
+BOOTLOADER_BAUD ?= $(BAUD)
+
+# List of bootloader sources determined by esp-idf/examples/get-started/hello-world
+# TODO HowTo generate this list
+ESP_SDK_BOOTLOADER_SRCS = \
+  components/bootloader/subproject/main/bootloader_start.c \
+  components/bootloader/subproject/components/micro-ecc/uECC_verify_antifault.c \
+  components/bootloader_support/src/bootloader_clock_init.c \
+  components/bootloader_support/src/bootloader_clock_loader.c \
+  components/bootloader_support/src/bootloader_common.c \
+  components/bootloader_support/src/bootloader_common_loader.c \
+  components/bootloader_support/src/bootloader_console.c \
+  components/bootloader_support/src/bootloader_console_loader.c \
+  components/bootloader_support/src/bootloader_efuse_$(CPU).c \
+  components/bootloader_support/src/bootloader_flash.c \
+  components/bootloader_support/src/bootloader_flash_config_$(CPU).c \
+  components/bootloader_support/src/bootloader_init.c \
+  components/bootloader_support/src/bootloader_mem.c \
+  components/bootloader_support/src/bootloader_panic.c \
+  components/bootloader_support/src/bootloader_random.c \
+  components/bootloader_support/src/bootloader_random_$(CPU).c \
+  components/bootloader_support/src/bootloader_utility.c \
+  components/bootloader_support/src/$(CPU)/bootloader_$(CPU).c \
+  components/bootloader_support/src/$(CPU)/bootloader_sha.c \
+  components/bootloader_support/src/$(CPU)/bootloader_soc.c \
+  components/bootloader_support/src/esp_image_format.c \
+  components/bootloader_support/src/flash_encrypt.c \
+  components/bootloader_support/src/flash_partitions.c \
+  components/bootloader_support/src/flash_qio_mode.c \
+  components/bootloader_support/src/secure_boot.c \
+  components/efuse/$(CPU)/esp_efuse_fields.c \
+  components/efuse/$(CPU)/esp_efuse_table.c \
+  components/efuse/$(CPU)/esp_efuse_utility.c \
+  components/efuse/src/esp_efuse_api.c \
+  components/efuse/src/esp_efuse_fields.c \
+  components/efuse/src/esp_efuse_utility.c \
+  components/esp_common/src/esp_err_to_name.c \
+  components/esp_hw_support/compare_set.c \
+  components/esp_hw_support/cpu_util.c \
+  components/esp_hw_support/port/$(CPU)/chip_info.c \
+  components/esp_hw_support/port/$(CPU)/rtc_clk.c \
+  components/esp_hw_support/port/$(CPU)/rtc_clk_init.c \
+  components/esp_hw_support/port/$(CPU)/rtc_init.c \
+  components/esp_hw_support/port/$(CPU)/rtc_pm.c \
+  components/esp_hw_support/port/$(CPU)/rtc_sleep.c \
+  components/esp_hw_support/port/$(CPU)/rtc_time.c \
+  components/esp_hw_support/port/$(CPU)/rtc_wdt.c \
+  components/esp_rom/patches/esp_rom_crc.c \
+  components/esp_rom/patches/esp_rom_sys.c \
+  components/esp_rom/patches/esp_rom_tjpgd.c \
+  components/esp_rom/patches/esp_rom_uart.c \
+  components/esp_system/esp_err.c \
+  components/hal/cpu_hal.c \
+  components/hal/mpu_hal.c \
+  components/hal/wdt_hal_iram.c \
+  components/log/log_buffers.c \
+  components/log/log.c \
+  components/log/log_noos.c \
+  components/newlib/syscalls.c \
+  components/soc/$(CPU)/adc_periph.c \
+  components/soc/$(CPU)/dac_periph.c \
+  components/soc/$(CPU)/gpio_periph.c \
+  components/soc/$(CPU)/i2c_periph.c \
+  components/soc/$(CPU)/i2s_periph.c \
+  components/soc/$(CPU)/interrupts.c \
+  components/soc/$(CPU)/lcd_periph.c \
+  components/soc/$(CPU)/ledc_periph.c \
+  components/soc/$(CPU)/mcpwm_periph.c \
+  components/soc/$(CPU)/pcnt_periph.c \
+  components/soc/$(CPU)/rmt_periph.c \
+  components/soc/$(CPU)/rtc_io_periph.c \
+  components/soc/$(CPU)/sdio_slave_periph.c \
+  components/soc/$(CPU)/sdmmc_periph.c \
+  components/soc/$(CPU)/sigmadelta_periph.c \
+  components/soc/$(CPU)/spi_periph.c \
+  components/soc/$(CPU)/timer_periph.c \
+  components/soc/$(CPU)/touch_sensor_periph.c \
+  components/soc/$(CPU)/uart_periph.c \
+  components/soc/lldesc.c \
+  components/spi_flash/$(CPU)/spi_flash_rom_patch.c \
+  components/xtensa/eri.c \
+  components/xtensa/xt_trax.c \
+
+ifneq (,$(filter esp32,$(CPU)))
+  ESP_SDK_BOOTLOADER_SRCS += components/efuse/src/esp_efuse_api_key_esp32.c
+else
+  ESP_SDK_BOOTLOADER_SRCS += components/efuse/src/esp_efuse_api_key_esp32xx.c
+endif
+
+ESP_SDK_BOOTLOADER_ASMSRC = \
+  components/esp_rom/patches/esp_rom_longjmp.S \
+
+# Bootloader sdkconfig.h defined in CURDIR directory.
+INCLUDES = \
+  -I$(dir $(RIOTBUILD_CONFIG_HEADER_C)) \
+  -I$(CURDIR) \
+  -I$(ESP32_SDK_DIR)/components \
+  -I$(ESP32_SDK_DIR)/components/bootloader/subproject/components/micro-ecc \
+  -I$(ESP32_SDK_DIR)/components/bootloader/subproject/components/micro-ecc/micro-ecc \
+  -I$(ESP32_SDK_DIR)/components/bootloader_support/bootloader_flash/include \
+  -I$(ESP32_SDK_DIR)/components/bootloader_support/include \
+  -I$(ESP32_SDK_DIR)/components/bootloader_support/include_bootloader \
+  -I$(ESP32_SDK_DIR)/components/efuse/include \
+  -I$(ESP32_SDK_DIR)/components/efuse/private_include \
+  -I$(ESP32_SDK_DIR)/components/efuse/$(CPU)/include \
+  -I$(ESP32_SDK_DIR)/components/efuse/$(CPU)/private_include \
+  -I$(ESP32_SDK_DIR)/components/esp_common/include \
+  -I$(ESP32_SDK_DIR)/components/esp_hw_support/include \
+  -I$(ESP32_SDK_DIR)/components/esp_hw_support/include/soc \
+  -I$(ESP32_SDK_DIR)/components/esp_hw_support/include/soc/$(CPU) \
+  -I$(ESP32_SDK_DIR)/components/esp_hw_support/port/$(CPU) \
+  -I$(ESP32_SDK_DIR)/components/esp_hw_support/port/$(CPU)/private_include \
+  -I$(ESP32_SDK_DIR)/components/esp_rom/$(CPU) \
+  -I$(ESP32_SDK_DIR)/components/esp_rom/include \
+  -I$(ESP32_SDK_DIR)/components/esp_rom/include/$(CPU) \
+  -I$(ESP32_SDK_DIR)/components/hal/$(CPU)/include \
+  -I$(ESP32_SDK_DIR)/components/hal/include \
+  -I$(ESP32_SDK_DIR)/components/hal/platform_port/include \
+  -I$(ESP32_SDK_DIR)/components/log/include \
+  -I$(ESP32_SDK_DIR)/components/newlib/platform_include \
+  -I$(ESP32_SDK_DIR)/components/soc/$(CPU)/. \
+  -I$(ESP32_SDK_DIR)/components/soc/$(CPU)/include \
+  -I$(ESP32_SDK_DIR)/components/soc/include \
+  -I$(ESP32_SDK_DIR)/components/spi_flash/include \
+  -I$(ESP32_SDK_DIR)/components/spi_flash/include/spi_flash \
+  -I$(ESP32_SDK_DIR)/components/xtensa/$(CPU)/include \
+  -I$(ESP32_SDK_DIR)/components/xtensa/include \
+  #
+
+# BOOTLOADER_BUILD=1 signals to the SDK that's a bootloader build.
+CFLAGS = \
+  -include '$(RIOTBUILD_CONFIG_HEADER_C)' \
+  -mlongcalls \
+  -Wno-frame-address \
+  -ffunction-sections \
+  -fdata-sections \
+  -Wall \
+  -Werror=all \
+  -Wno-error=unused-function \
+  -Wno-error=unused-variable \
+  -Wno-error=deprecated-declarations \
+  -Wextra \
+  -Wno-unused-parameter \
+  -Wno-sign-compare \
+  -ggdb \
+  -Os \
+  -freorder-blocks \
+  -fstrict-volatile-bitfields \
+  -Wno-error=unused-but-set-variable \
+  -fno-jump-tables \
+  -fno-tree-switch-conversion \
+  -fno-stack-protector \
+  -std=gnu99 \
+  -Wno-old-style-declaration \
+  -D_GNU_SOURCE \
+  -DESP_PLATFORM \
+  -DBOOTLOADER_BUILD=1 \
+  -DRIOT_BOOTLOADER_BAUD=$(BOOTLOADER_BAUD) \
+  -DRIOT_FLASH_SIZE=$(FLASH_SIZE) \
+  -DWITH_POSIX \
+  -DHAVE_CONFIG_H \
+  -MD \
+  -MT \
+  #
+
+ifneq (,$(filter esp32 esp32s2 esp32s3,$(CPU)))
+  ESP_SDK_BOOTLOADER_ADD_LINK_FLAGS += -L$(ESP32_SDK_DIR)/components/xtensa/$(CPU) -lxt_hal
+endif
+
+ifneq (,$(filter esp32 esp32s2,$(CPU)))
+  ESP_SDK_BOOTLOADER_ADD_LINK_FLAGS += \
+    -T$(ESP32_SDK_DIR)/components/esp_rom/$(CPU)/ld/$(CPU).rom.newlib-funcs.ld \
+    -T$(ESP32_SDK_DIR)/components/esp_rom/$(CPU)/ld/$(CPU).rom.spiflash.ld \
+    #
+endif
+
+# Bootloader link flags. We use the SDK source and linking files instead of the
+# RIOT-OS ones to link the bootloader. Note that we also use the unmodified
+# SDK libraries.
+LINKFLAGS = \
+  -mlongcalls \
+  -Wno-frame-address \
+  -o $(ESP_SDK_BOOTLOADER_DIR)/bootloader.elf \
+  -Wl,--cref \
+  -Wl,--defsym=IDF_TARGET_ESP32=0 \
+  -Wl,--gc-sections \
+  -fno-lto \
+  -fno-rtti \
+  -u __assert_func \
+  -u abort \
+  -u __ubsan_include \
+  -u bootloader_hooks_include \
+  -Wl,--start-group \
+  $(ESP_SDK_BOOTLOADER_OBJS) \
+  $(ESP_SDK_BOOTLOADER_ADDOBJS) \
+  $(ESP_SDK_BOOTLOADER_ASMOBJS) \
+  -Lgcc \
+  $(ESP_SDK_BOOTLOADER_ADD_LINK_FLAGS) \
+  -T$(ESP32_SDK_DIR)/components/bootloader/subproject/main/ld/$(CPU)/bootloader.ld \
+  -T$(ESP32_SDK_DIR)/components/bootloader/subproject/main/ld/$(CPU)/bootloader.rom.ld \
+  -T$(ESP32_SDK_DIR)/components/soc/$(CPU)/ld/$(CPU).peripherals.ld \
+  -T$(ESP32_SDK_DIR)/components/esp_rom/$(CPU)/ld/$(CPU).rom.ld \
+  -T$(ESP32_SDK_DIR)/components/esp_rom/$(CPU)/ld/$(CPU).rom.api.ld \
+  -T$(ESP32_SDK_DIR)/components/esp_rom/$(CPU)/ld/$(CPU).rom.libgcc.ld \
+  -Wl,--end-group \
+  -Wl,-EL \
+
+# Build the bootloader on the application directory as it depends on the current
+# app settings from riotbuild.h.
+ESP_SDK_BOOTLOADER_DIR = $(BINDIR)/$(MODULE)
+ESP_SDK_BOOTLOADER_BIN = $(ESP_SDK_BOOTLOADER_DIR)/bootloader.bin
+ESP_SDK_BOOTLOADER_ELF = $(ESP_SDK_BOOTLOADER_DIR)/bootloader.elf
+
+# Objects that need to be filtered out because they are not part of the SDK
+# but are used as submodules and required by the Secure Boot which is not yet
+# supported due to a conflict of the packages `tinycrypt` and `micro-ecc`
+ESP_SDK_BOOTLOADER_OBJ_FILTER = \
+  components/bootloader/subproject/components/micro-ecc/uECC_verify_antifault.o \
+  components/bootloader_support/src/secure_boot.o \
+  components/bootloader_support/src/flash_encrypt.o \
+  #
+
+ESP_SDK_BOOTLOADER_OBJS = \
+  $(addprefix $(ESP_SDK_BOOTLOADER_DIR)/, \
+              $(filter-out $(ESP_SDK_BOOTLOADER_OBJ_FILTER), \
+                           $(ESP_SDK_BOOTLOADER_SRCS:%.c=%.o)))
+
+ESP_SDK_BOOTLOADER_ASMOBJS = \
+  $(addprefix $(ESP_SDK_BOOTLOADER_DIR)/, \
+              $(ESP_SDK_BOOTLOADER_ASMSRC:%.S=%.o))
+
+ESP_SDK_BOOTLOADER_ADDOBJS = \
+  $(addprefix $(ESP_SDK_BOOTLOADER_DIR)/,stub.o) \
+
+DEPS := $(ESP_SDK_BOOTLOADER_OBJS:%.o=%.d) $(ESP_SDK_BOOTLOADER_ASMOBJS:.o=.d)
+-include $(DEPS)
+
+# Main module dependency. We only build the bootloader.bin from this module.
+$(MODULE).module: $(ESP_SDK_BOOTLOADER_BIN)
+
+OBJ_DEPS += $(CURDIR)/sdkconfig.h
+
+$(ESP_SDK_BOOTLOADER_OBJS): \
+$(ESP_SDK_BOOTLOADER_DIR)/%.o: $(ESP32_SDK_DIR)/%.c $(OBJ_DEPS)
+	$(Q)mkdir -p $(dir $@)
+	$(Q)$(CCACHE) $(CC) \
+	  $(CFLAGS) $(INCLUDES) -MMD -MP -c $(abspath $<) -o $@
+
+$(ESP_SDK_BOOTLOADER_ASMOBJS): \
+$(ESP_SDK_BOOTLOADER_DIR)/%.o: $(ESP32_SDK_DIR)/%.S
+	$(Q)mkdir -p $(dir $@)
+	$(Q)$(AS) $(ASFLAGS) -o $@ $(abspath $<)
+
+$(ESP_SDK_BOOTLOADER_ADDOBJS): \
+$(ESP_SDK_BOOTLOADER_DIR)/%.o: $(CURDIR)/stub.c $(OBJ_DEPS)
+	$(Q)mkdir -p $(dir $@)
+	$(Q)$(CCACHE) $(CC) \
+	  $(CFLAGS) $(INCLUDES) -MMD -MP -c $(abspath $<) -o $@
+
+$(ESP_SDK_BOOTLOADER_DIR):
+	mkdir -p $@
+
+$(ESP_SDK_BOOTLOADER_ELF): \
+    $(ESP_SDK_BOOTLOADER_OBJS) $(ESP_SDK_BOOTLOADER_ASMOBJS) \
+    $(ESP_SDK_BOOTLOADER_ADDOBJS) | $(ESP_SDK_BOOTLOADER_DIR)
+	$(Q)$(CC) -o $@ $(LINKFLAGS) -Wl,-Map=$(@:%.elf=%.map)
+
+FLASH_CHIP = $(CPU)
+ESPTOOL ?= $(RIOTTOOLS)/esptools/esptool_v3.2.py
+# TODO: These should be exported/configurable from the app side. That would
+# require to export these values.
+FLASH_MODE ?= dout
+FLASH_FREQ ?= 40m
+FLASH_SIZE ?= 4
+
+# We use esptool to extract a version 1 app from the bootloader.elf. This is
+# like the regular objdump binary file but it contains a 16 byte header which
+# specifies the flash size, mode and speed that the ROM bootloader uses to load
+# this second-stage bootloader image.
+$(ESP_SDK_BOOTLOADER_BIN): $(ESP_SDK_BOOTLOADER_ELF)
+	$(Q)$(ESPTOOL) --chip $(FLASH_CHIP) elf2image --flash_mode $(FLASH_MODE) \
+	  --flash_size $(FLASH_SIZE)MB --flash_freq $(FLASH_FREQ) -o $@ $<

cpu/esp32/bootloader/sdkconfig.h

@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2021 iosabi
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     pkg_esp32_sdk
+ * @{
+ *
+ * @file
+ * @brief       RIOT-OS modification of the bootloader SDK configuration
+ *
+ * The bootloader build of the ESP32 SDK needs some settings from the SDK
+ * configuration. These are normally generated by the menuconfig in the vendor
+ * SDK.
+ *
+ * Some of these parameters are configurable by the application. For example,
+ * the UART baudrate used by the console and the verbose level of the
+ * bootloader.
+ *
+ * @author      iosabi <iosabi@protonmail.com>
+ */
+
+#ifndef SDKCONFIG_H
+#define SDKCONFIG_H
+
+#ifndef DOXYGEN
+
+#include "esp_idf_ver.h"
+#include "sdkconfig_default.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if MODULE_ESP_LOG_COLORED
+#define CONFIG_LOG_COLORS   1
+#endif
+
+#ifndef CONFIG_BOOTLOADER_LOG_LEVEL
+/*
+ * SDK Log levels:
+ *
+ *  0 = NONE
+ *  1 = ERROR
+ *  2 = WARN
+ *  3 = INFO
+ *  4 = DEBUG
+ *  5 = VERBOSE
+ */
+#if MODULE_ESP_LOG_STARTUP
+#define CONFIG_BOOTLOADER_LOG_LEVEL     3   /* INFO */
+#else
+#define CONFIG_BOOTLOADER_LOG_LEVEL     0   /* NONE */
+#endif
+#endif
+
+#if FLASH_MODE_QIO
+#define CONFIG_FLASHMODE_QIO            1
+#define CONFIG_ESPTOOLPY_FLASHMODE_QIO  1
+#elif FLASH_MODE_QOUT
+#define CONFIG_FLASHMODE_QOUT           1
+#define CONFIG_ESPTOOLPY_FLASHMODE_QOUT 1
+#elif FLASH_MODE_DIO
+#define CONFIG_FLASHMODE_DIO            1
+#define CONFIG_ESPTOOLPY_FLASHMODE_DIO  1
+#elif FLASH_MODE_DOUT
+#define CONFIG_FLASHMODE_DOUT           1
+#define CONFIG_ESPTOOLPY_FLASHMODE_DOUT 1
+#else
+#error "Unknown flash mode selected."
+#endif
+
+/*
+ * Bootloader output baudrate, defined by the app settings as BAUD or
+ * BOOTLOADER_BAUD.
+ */
+#define CONFIG_ESP_CONSOLE_UART_BAUDRATE (RIOT_BOOTLOADER_BAUD)
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* DOXYGEN */
+/** @} */
+
+#endif /* SDKCONFIG_H */

cpu/esp32/bootloader/sdkconfig_default.h

@@ -0,0 +1,40 @@
+/*
+ * Generated by ./update_mk.sh, don't modify directly.
+ * Default CONFIG_ parameters from the SDK package.
+ */
+
+#ifndef SDKCONFIG_DEFAULT_H
+#define SDKCONFIG_DEFAULT_H
+
+#ifndef DOXYGEN
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ
+#define CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ 160
+#endif
+
+#define CONFIG_BOOTLOADER_VDDSDIO_BOOST_1_9V 1
+#define CONFIG_BOOTLOADER_OFFSET_IN_FLASH 0x1000
+#define CONFIG_BOOTLOADER_FLASH_XMC_SUPPORT 1
+#define CONFIG_CONSOLE_UART_NUM 0
+#define CONFIG_EFUSE_CODE_SCHEME_COMPAT_3_4 1
+#define CONFIG_EFUSE_MAX_BLK_LEN 192
+#define CONFIG_ESP_CONSOLE_UART 1
+#define CONFIG_ESP_CONSOLE_UART_NUM 0
+#define CONFIG_ESP32_DEBUG_OCDAWARE 1
+#define CONFIG_ESP32_XTAL_FREQ 40
+#define CONFIG_IDF_FIRMWARE_CHIP_ID 0x0000
+#define CONFIG_LOG_DEFAULT_LEVEL 3
+#define CONFIG_LOG_TIMESTAMP_SOURCE_RTOS 1
+#define CONFIG_PARTITION_TABLE_OFFSET 0x8000
+#define CONFIG_SPI_FLASH_ROM_DRIVER_PATCH 1
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* DOXYGEN */
+#endif /* SDKCONFIG_DEFAULT_H */

cpu/esp32/bootloader/stub.c

@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2022 Gunar Schorcht
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+#define PTHREAD_CANCEL_DISABLE 1
+/*
+ * This is a dummy function to avoid undefined references when linking
+ * against newlib and module pthread is not used.
+ */
+int pthread_setcancelstate(int state, int *oldstate)
+{
+    if (oldstate) {
+        *oldstate = PTHREAD_CANCEL_DISABLE;
+    }
+    return 0;
+}

cpu/esp_common/Makefile.include

@@ -132,8 +132,8 @@ $(ELFFILE).bin: $(ELFFILE)
 # Convert .elf and .csv to .bin files at build time, but make them available for
 # tests at flash time. These can't be added to FLASHDEPS because they depend on
 # on ELFFILE and would trigger a rebuild with "flash-only".
-BUILD_FILES += $(FLASHFILE) $(BINDIR)/partitions.bin
-TEST_EXTRA_FILES += $(FLASHFILE) $(BINDIR)/partitions.bin
+BUILD_FILES += $(FLASHFILE) $(BINDIR)/partitions.bin $(BOOTLOADER_BIN)
+TEST_EXTRA_FILES += $(FLASHFILE) $(BINDIR)/partitions.bin $(BOOTLOADER_BIN)
 
 # Default partition table with no OTA. Can be replaced with a custom partition
 # table setting PARTITION_TABLE_CSV.

makefiles/tools/esptool.inc.mk

@@ -1,11 +1,15 @@
+ifneq ($(CPU),esp32)
+
 ifneq (,$(filter esp_log_colored,$(USEMODULE)))
   BOOTLOADER_COLOR = _colors
 endif
 ifneq (,$(filter esp_log_startup,$(USEMODULE)))
   BOOTLOADER_INFO = _info
 endif
-
-BOOTLOADER_BIN = bootloader$(BOOTLOADER_COLOR)$(BOOTLOADER_INFO).bin
+# Full path to the bootloader binary. In the ESP32 case this is set by the
+# esp_bootloader module.
+BOOTLOADER_BIN ?= $(RIOTCPU)/$(CPU)/bin/bootloader$(BOOTLOADER_COLOR)$(BOOTLOADER_INFO).bin
+endif
 
 ESPTOOL ?= $(RIOTTOOLS)/esptools/esptool.py
 
@@ -20,7 +24,7 @@ else
   FFLAGS += --chip $(FLASH_CHIP) --port $(PROG_DEV) --baud $(PROGRAMMER_SPEED)
   FFLAGS += --before default_reset write_flash -z
   FFLAGS += --flash_mode $(FLASH_MODE) --flash_freq $(FLASH_FREQ)
-  FFLAGS += $(BOOTLOADER_POS) $(RIOTCPU)/$(CPU)/bin/$(BOOTLOADER_BIN)
+  FFLAGS += $(BOOTLOADER_POS) $(BOOTLOADER_BIN)
   FFLAGS += 0x8000 $(BINDIR)/partitions.bin
   FFLAGS += 0x10000 $(FLASHFILE)
 endif
@@ -45,7 +49,7 @@ else
 	$(Q)dd if=/dev/zero bs=1M count=$(FLASH_SIZE) | \
 	  tr "\\000" "\\377" > tmp.bin && cat tmp.bin | \
 		head -c $$(($(BOOTLOADER_POS))) | \
-		cat - $(RIOTCPU)/$(CPU)/bin/$(BOOTLOADER_BIN) tmp.bin | \
+		cat - $(BOOTLOADER_BIN) tmp.bin | \
 		head -c $$((0x8000)) | \
 		cat - $(BINDIR)/partitions.bin tmp.bin | \
 		head -c $$((0x10000)) | \