First commit. It works on the ESP32_DevKitJ_v1 hardware.

Author: Spritetm

.gitignore

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+build/
+sdkconfig.old
+*.nes
+

Makefile

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+#
+# This is a project Makefile. It is assumed the directory this Makefile resides in is a
+# project subdirectory.
+#
+
+PROJECT_NAME := nesemu
+
+include $(IDF_PATH)/make/project.mk
+

components/bootloader/Kconfig.projbuild

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+menu "Bootloader config"
+choice LOG_BOOTLOADER_LEVEL
+   bool "Bootloader log verbosity"
+   default LOG_BOOTLOADER_LEVEL_WARN
+   help
+       Specify how much output to see in bootloader logs.
+
+config LOG_BOOTLOADER_LEVEL_NONE
+   bool "No output"
+config LOG_BOOTLOADER_LEVEL_ERROR
+   bool "Error"
+config LOG_BOOTLOADER_LEVEL_WARN
+   bool "Warning"
+config LOG_BOOTLOADER_LEVEL_INFO
+   bool "Info"
+config LOG_BOOTLOADER_LEVEL_DEBUG
+   bool "Debug"
+config LOG_BOOTLOADER_LEVEL_VERBOSE
+   bool "Verbose"
+endchoice
+
+config LOG_BOOTLOADER_LEVEL
+	int
+	default 0 if LOG_BOOTLOADER_LEVEL_NONE
+	default 1 if LOG_BOOTLOADER_LEVEL_ERROR
+	default 2 if LOG_BOOTLOADER_LEVEL_WARN
+	default 3 if LOG_BOOTLOADER_LEVEL_INFO
+	default 4 if LOG_BOOTLOADER_LEVEL_DEBUG
+	default 5 if LOG_BOOTLOADER_LEVEL_VERBOSE
+
+endmenu

components/bootloader/Makefile.projbuild

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+#
+# Bootloader component
+#
+# The bootloader is not a real component that gets linked into the project.
+# Instead it is an entire standalone project ( in src/) that gets built in 
+# the upper projects build directory. This Makefile.projbuild provides the 
+# glue to  build the bootloader project from the original project. It 
+# basically runs Make in the src/ directory but it needs to zero some variables
+# the ESP-IDF project.mk makefile exports first, to not let them interfere.
+#
+ifeq ("$(IS_BOOTLOADER_BUILD)","")
+
+BOOTLOADER_COMPONENT_PATH := $(COMPONENT_PATH)
+BOOTLOADER_BUILD_DIR=$(BUILD_DIR_BASE)/bootloader
+BOOTLOADER_BIN=$(BOOTLOADER_BUILD_DIR)/bootloader.bin
+
+.PHONY: bootloader-clean bootloader-flash bootloader $(BOOTLOADER_BIN)
+
+$(BOOTLOADER_BIN): $(COMPONENT_PATH)/src/sdkconfig
+	$(Q) PROJECT_PATH= \
+	BUILD_DIR_BASE=$(BOOTLOADER_BUILD_DIR) \
+	$(MAKE) -C $(BOOTLOADER_COMPONENT_PATH)/src MAKEFLAGS= V=$(V) TARGET_BIN_LAYOUT="$(BOOTLOADER_TARGET_BIN_LAYOUT)" $(BOOTLOADER_BIN)
+
+bootloader-clean:
+	$(Q) PROJECT_PATH= \
+	BUILD_DIR_BASE=$(BOOTLOADER_BUILD_DIR) \
+	$(MAKE) -C $(BOOTLOADER_COMPONENT_PATH)/src app-clean MAKEFLAGS= V=$(V)
+
+clean: bootloader-clean
+
+bootloader: $(BOOTLOADER_BIN)
+	@echo "Bootloader built. Default flash command is:"
+	@echo "$(ESPTOOLPY_WRITE_FLASH) 0x1000 $(BOOTLOADER_BIN)"
+
+all_binaries: $(BOOTLOADER_BIN)
+
+ESPTOOL_ALL_FLASH_ARGS += 0x1000 $(BOOTLOADER_BIN)
+
+# synchronise the project level config to the component's
+# config
+$(COMPONENT_PATH)/src/sdkconfig: $(PROJECT_PATH)/sdkconfig
+	$(Q) cp $< $@
+
+# bootloader-flash calls flash in the bootloader dummy project
+bootloader-flash: $(BOOTLOADER_BIN)
+	$(MAKE) -C $(BOOTLOADER_COMPONENT_PATH)/src flash MAKEFLAGS= V=$(V)
+
+else
+CFLAGS += -D BOOTLOADER_BUILD=1 -I $(IDF_PATH)/components/esp32/include 
+
+endif

components/bootloader/src/.gitignore

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+build
+sdkconfig

components/bootloader/src/Makefile

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+#
+# This is a project Makefile. It is assumed the directory this Makefile resides in is a
+# project subdirectory.
+#
+
+PROJECT_NAME := bootloader
+COMPONENTS := esptool_py bootloader log
+
+# The bootloader pseudo-component is also included in this build, for its Kconfig.projbuild to be included.
+#
+# IS_BOOTLOADER_BUILD tells the component Makefile.projbuild to be a no-op
+IS_BOOTLOADER_BUILD := 1
+
+#We cannot include the esp32 component directly but we need its includes. 
+#This is fixed by adding CFLAGS from Makefile.projbuild
+
+include $(IDF_PATH)/make/project.mk

components/bootloader/src/main/bootloader_config.h

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+// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#ifndef __BOOT_CONFIG_H__
+#define __BOOT_CONFIG_H__
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+#define BOOT_VERSION "V0.1"
+#define SPI_SEC_SIZE 0x1000
+#define MEM_CACHE(offset)   (uint8_t *)(0x3f400000 + (offset))
+#define CACHE_READ_32(offset)   ((uint32_t *)(0x3f400000 + (offset)))
+#define PARTITION_ADD 0x4000
+#define PARTITION_MAGIC 0x50AA
+#define IROM_LOW    0x400D0000
+#define IROM_HIGH   0x40400000
+#define DROM_LOW    0x3F400000
+#define DROM_HIGH   0x3F800000
+#define RTC_IRAM_LOW  0x400C0000
+#define RTC_IRAM_HIGH 0x400C2000
+#define RTC_DATA_LOW  0x50000000
+#define RTC_DATA_HIGH 0x50002000
+
+/*spi mode,saved in third byte in flash */
+enum {
+    SPI_MODE_QIO,
+    SPI_MODE_QOUT,
+    SPI_MODE_DIO,
+    SPI_MODE_DOUT,
+    SPI_MODE_FAST_READ,
+    SPI_MODE_SLOW_READ
+};
+/* spi speed*/
+enum {
+    SPI_SPEED_40M,
+    SPI_SPEED_26M,
+    SPI_SPEED_20M,
+    SPI_SPEED_80M = 0xF
+};
+/*suppport flash size in esp32 */
+enum {
+    SPI_SIZE_1MB = 0,
+    SPI_SIZE_2MB,
+    SPI_SIZE_4MB,
+    SPI_SIZE_8MB,
+    SPI_SIZE_16MB,
+    SPI_SIZE_MAX
+};
+
+
+struct flash_hdr {
+    char magic;
+    char blocks;
+    char spi_mode;      /* flag of flash read mode in unpackage and usage in future */
+    char spi_speed: 4;  /* low bit */
+    char spi_size: 4;
+    unsigned int entry_addr;
+    uint8_t encrypt_flag;    /* encrypt flag */
+    uint8_t secury_boot_flag; /* secury boot flag */
+    char extra_header[14]; /* ESP32 additional header, unused by second bootloader */
+};
+
+/* each header of flash bin block */
+struct block_hdr {
+    unsigned int load_addr;
+    unsigned int data_len;
+};
+
+/* OTA selection structure (two copies in the OTA data partition.)
+
+   Size of 32 bytes is friendly to flash encryption */
+typedef struct {
+    uint32_t ota_seq;
+    uint8_t  seq_label[24];
+    uint32_t crc; /* CRC32 of ota_seq field only */
+} ota_select;
+
+typedef struct {
+    uint32_t offset;
+    uint32_t size;
+} partition_pos_t;
+
+typedef struct {
+	uint16_t magic;
+	uint8_t  type;        /* partition Type */
+    uint8_t  subtype;     /* part_subtype */
+    partition_pos_t pos;
+	uint8_t  label[16];    /* label for the partition */
+    uint8_t  reserved[4];     /* reserved */
+} partition_info_t;
+
+#define PART_TYPE_APP 0x00
+#define PART_SUBTYPE_FACTORY  0x00
+#define PART_SUBTYPE_OTA_FLAG 0x10
+#define PART_SUBTYPE_OTA_MASK 0x0f
+#define PART_SUBTYPE_TEST     0x20
+
+#define PART_TYPE_DATA 0x01
+#define PART_SUBTYPE_DATA_OTA 0x00
+#define PART_SUBTYPE_DATA_RF  0x01
+#define PART_SUBTYPE_DATA_WIFI 0x02
+
+#define PART_TYPE_END 0xff
+#define PART_SUBTYPE_END 0xff
+
+#define SPI_ERROR_LOG "spi flash error"
+
+typedef struct {
+    partition_pos_t ota_info;
+    partition_pos_t factory;
+    partition_pos_t test;
+    partition_pos_t ota[16];
+    uint32_t app_count;
+    uint32_t selected_subtype;
+} bootloader_state_t;
+
+void boot_cache_redirect( uint32_t pos, size_t size );
+uint32_t get_bin_len(uint32_t pos);
+
+bool flash_encrypt(bootloader_state_t *bs);
+bool secure_boot(void);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __BOOT_CONFIG_H__ */