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build-and-run-native-app.md

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Build and run ELF application

ESP32 toolchain distributed in crosstool-NG project releases is able to build ELF executables without using IDF dependencies (e.g.: bootloader and other components).

All the minimal but essential code for chip initialization and syscall functions are contained in libgloss which is a part of xtensa-esp32-elf toolchain. It means that generated ELF file can be executed on a bare-metal ESP32 chip or on QEMU simulation.

Spec files

To link an application with libgloss library use spec files which are contained in xtensa ESP32 toolchain.

Specs files to enable semihosting could be used.

  • Semihosting - mechanism that enables code running on an ESP32 to communicate with and use the I/O of the host computer. For example, it can be used for writing to host's terminal or host's file during a run on ESP32 or QEMU.

NOTE: when semihosting operation is executed the target processor is simply stopped until data is being transferred to host.

This could slow down the performance of an executed application.

QEMU specs

  • sim.elf.specs - build ELF for running on QEMU
  • sys.qemu.specs - use I/O operations using semihosting in QEMU

OpenOCD specs

  • board.elf.specs - build ELF for running on bare-metal ESP32
  • sys.openocd.specs - use I/O operations using semihosting in openOCD

Example

main.c listing:

#include <stdio.h>
int main() {
   printf("Hello, World!\n");
}

QEMU

Build

xtensa-esp32-elf-gcc main.c -specs=sim.elf.specs [-specs=sys.qemu.specs]

Run

qemu-system-xtensa -nographic -monitor null -cpu esp32 -M esp32 -kernel ./a.out [--semihosting]

Bare-metal ESP32

Build

xtensa-esp32-elf-gcc main.c -specs=board.elf.specs [-specs=sys.openocd.specs]

Run

Step 1:

Connect ESP32 to host via JTAG interface.

Step 2:

Run OpenOCD session.

openocd -c 'set ESP_RTOS none' -f board/esp32-wrover-kit-3.3v.cfg

Step 3:

Load ELF file to the RAM through JTAG and run the application.

  xtensa-esp32-elf-gdb ./a.out
  (gdb) target remote :3333
  (gdb) mon reset halt
  (gdb) load
  (gdb) continue