Reference: https://docs.espressif.com/projects/esp-idf/en/v3.3.2/get-started/macos-setup.html

Prerequisites:

Python3 and git ( I use brew ). Python should already be in your path. 

esptool   ( pip3 install esptool )

After flashing the firmware - Ampy is used to run the initial configuration scripts.

 --- Create two directories for the devtools. 

cd ~
mkdir ~/esp
mkdir ~/Micropython

cd ~/esp
git clone -b v3.3.2 --recursive https://github.com/espressif/esp-idf.git

  --- Add the newly installed IDF path to your environment.  I use .bash_profile

export PATH="$PATH:$HOME/esp/xtensa-esp32-elf/bin"
export IDF_PATH=($HOME)/esp/esp-idf
   

Dont forget to source the env file to activate the new settings:

source ~/.bash_profile

  --- Install the python requirements for the ESP-IDF

python3 -m pip install --user -r $IDF_PATH/requirements.txt

 --- Clone the micropython repository

cd ~/Micropython
git clone  https://github.com/micropython/micropython.git

Reference: https://github.com/micropython/micropython/tree/master

---  Build the cross-compiler

cd ~/Micropython/micropython/mpy-cross
make

 --- Modfy the Makefile

cd ~/Micropython/micropython/ports/esp32

 Edit the Makefile to have these variables set for the desired build

ESPIDF ?=$(HOME)/esp/esp-idf
BOARD ?= GENERIC_SPIRAM

--- Modify the partition file  partitions.csv

The below is how the file should look.  You should only have to change the last line, at the end from 0x200000   to   0x600000

# Notes: the offset of the partition table itself is set in
# $ESPIDF/components/partition_table/Kconfig.projbuild and the
# offset of the factory/ota_0 partition is set in makeimg.py
# Name,   Type, SubType, Offset,  Size, Flags
nvs,      data, nvs,     0x9000,  0x6000,
phy_init, data, phy,     0xf000,  0x1000,
factory,  app,  factory, 0x10000, 0x180000,
vfs,      data, fat,     0x200000, 0x600000,

--- Run make

make

A sub-directory will be created with the compile output ( including the firmware.bin )

build-GENERIC_SPIRAM

 --- Erase the flash, if needed

esptool.py --chip esp32 --port /dev/cu.SLAB_USBtoUART erase_flash

  --- Install the firmware.bin file onto the device

esptool.py --chip esp32 --port /dev/cu.SLAB_USBtoUART --baud 460800 write_flash -z 0x1000 firmware.bin

--- connect to the device with ampy and run the script below.  Do not copy to the device to run.

( the filesystem is remade - so this will destroy anything in the filesystem! )

import os

def df():
  s = os.statvfs('//')
  return ('{0} MB'.format((s[0]*s[3])/1048576))

def free(full=False):
  F = gc.mem_free()
  A = gc.mem_alloc()
  T = F+A
  P = '{0:.2f}%'.format(F/T*100)
  if not full: return P
  else : return ('Total:{0} Free:{1} ({2})'.format(T,F,P))

print('disk free: ', df())
print('memory free: ', free())

os.umount('/')
os.VfsFat.mkfs(bdev)
os.mount(bdev, '/')

print('disk free: ', df())
print('memory free: ', free())