tree ebfd7a079772f3677cd0a2425329287e788ffc6f
parent 0e08b946de43b860ed6713b7460031333d44dad7
author Leandro Pereira <leandro.pereira@intel.com> 1497378436 -0700
committer Anas Nashif <nashif@linux.intel.com> 1498062949 -0400

esp32: Use esptool.py to flash with 'make flash'

This flashes Zephyr at 0x1000: that's where the first stage bootloader,
part of the ESP32 ROM, expects to find an "image header".

The second-stage bootloader, part of ESP-IDF, isn't used by the Zephyr
port.  However, the bootloader can be used if desired; please refer to
the ESP-IDF documentation on how to set up partitions tables and use
the bootloader.

The following environment variables will affect the ESP32 flashing
process:

  Variable              Default value
  ESP_DEVICE            /dev/ttyUSB0
  ESP_BAUD_RATE         921600
  ESP_FLASH_SIZE        detect
  ESP_FLASH_FREQ        40m
  ESP_FLASH_MODE        dio
  ESP_TOOL              espidf

It's impossible to determine which serial port the ESP32 board is
connected to, as it uses a generic RS232-USB converter.  The default of
/dev/ttyUSB0 is provided as that's often the assigned name on a Linux
machine without any other such converters.

The baud rate of 921600bps is recommended.  If experiencing issues when
flashing, try halving the value a few times (460800, 230400, 115200,
etc).  It might be necessary to change the flash frequency or the flash
mode; please refer to the esptool documentation for guidance on these
settings.

If ${ESP_TOOL} is set to "espidf", the esptool.py script found within
ESP-IDF will be used.  Otherwise, this variable is handled as a path to
the tool.

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>