feature: add build framework support

Kconfig

@@ -141,13 +141,15 @@ mainmenu "Espressif IoT Development Framework Configuration"
 
                 Another option, useful for only very small and limited applications, is to only link
                 the .elf file of the application, such that it can be loaded directly into RAM over
-                JTAG. Note that since IRAM and DRAM sizes are very limited, it is not possible to
-                build any complex application this way. However for kinds of testing and debugging,
+                JTAG or UART. Note that since IRAM and DRAM sizes are very limited, it is not possible
+                to build any complex application this way. However for some kinds of testing and debugging,
                 this option may provide faster iterations, since the application does not need to be
                 written into flash.
-                Note that at the moment, ESP-IDF does not contain all the startup code required to
-                initialize the CPUs and ROM memory (data/bss). Therefore it is necessary to execute
-                a bit of ROM code prior to executing the application. A gdbinit file may look as follows (for ESP32):
+
+                Note: when APP_BUILD_TYPE_RAM is selected and loaded with JTAG, ESP-IDF does not contain
+                all the startup code required to initialize the CPUs and ROM memory (data/bss).
+                Therefore it is necessary to execute a bit of ROM code prior to executing the application.
+                A gdbinit file may look as follows (for ESP32):
 
                     # Connect to a running instance of OpenOCD
                     target remote :3333
@@ -169,6 +171,13 @@ mainmenu "Espressif IoT Development Framework Configuration"
 
                 Example gdbinit files for other targets can be found in tools/test_apps/system/gdb_loadable_elf/
 
+                When loading the BIN with UART, the ROM will jump to ram and run the app after finishing the ROM
+                startup code, so there's no additional startup initialization required. You can use the
+                `load_ram` in esptool.py to load the generated .bin file into ram and execute.
+
+                Example:
+                    esptool.py --chip {chip} -p {port} -b {baud} --no-stub load_ram {app.bin}
+
                 Recommended sdkconfig.defaults for building loadable ELF files is as follows.
                 CONFIG_APP_BUILD_TYPE_RAM is required, other options help reduce application
                 memory footprint.
@@ -189,9 +198,11 @@ mainmenu "Espressif IoT Development Framework Configuration"
                 select APP_BUILD_BOOTLOADER
                 select APP_BUILD_USE_FLASH_SECTIONS
 
-            config APP_BUILD_TYPE_ELF_RAM
+            config APP_BUILD_TYPE_RAM
                 bool
-                prompt "ELF file, loadable into RAM (EXPERIMENTAL))"
+                prompt "Build app runs entirely in RAM (EXPERIMENTAL)"
+                select APP_BUILD_GENERATE_BINARIES
+
         endchoice # APP_BUILD_TYPE
 
         # Hidden options, set according to the choice above
@@ -201,6 +212,16 @@ mainmenu "Espressif IoT Development Framework Configuration"
         config APP_BUILD_BOOTLOADER
             bool # Whether to build the bootloader
 
+        config APP_BUILD_TYPE_PURE_RAM_APP
+            bool
+            prompt "Build app without SPI_FLASH/PSRAM support (saves ram)"
+            depends on APP_BUILD_TYPE_RAM
+            help
+                If this option is enabled, external memory and related peripherals, such as Cache, MMU,
+                Flash and PSRAM, won't be initialized. Corresponding drivers won't be introduced either.
+                Components that depend on the spi_flash component will also be unavailable, such as
+                app_update, etc. When this option is enabled, about 26KB of RAM space can be saved.
+
         config APP_BUILD_USE_FLASH_SECTIONS
             bool # Whether to place code/data into memory-mapped flash sections