Thanks to Rui and Sara Santos for their book MicroPython ESP32 and ESP8266. I purchased 3 DoIT ESP32 DEVKIT V1 boards ($8 per) from Banggood and have done Module 1-2 and most of 3 before getting sidetracked. I hope people can help with this.

QUESTIONS

1. The “byte string” returned from the machine.unique_id  instruction has information both in hex (eg \xcb) and in ASCII (eg. n). Knowing almost nothing about any form of Python, how do I take this “byte string” and format it so as to display only a string of hex numbers?

2. When reading the pre-programmed MAC address information contained in the EFUSE from each board, the result in the high 24 bits has an extra 2 hex digits which are not part of the MAC address. Are they a checksum?  If not, what do they signify.

Problem: How to identify each board since the boards look completely identical. I can see absolutely no difference in labelling on either the board itself or on the ESP32-VROOM module. To differentiate, I labelled them 1 – 3 with a Sharpie. BUT, how to do this electronically? All boards have firmware v1.18.

A Clue from MicroPython Documentation, Release 1.18, page 60, Miscellaneous functions:       machine.unique_id()

“Returns a byte string with a unique identifier of a board/SoC…In some MicroPython ports, ID corresponds to the network MAC address.”  This is true for these particular boards.

Using CODE1 below, all 3 boards return a consistent “byte string” (using either Mu or Thonny)

board1     b’\xec\x94\xcbnF\xe8′
board2     b’\xec\x94\xcbp$4′
board3     b’X\xbf%\x93\xd2h’

Then I used the example from MicroPython Documentation, Release 1.18, page 393:  Accessing peripherals directly via registers, to learn how to read and print out the two EFUSE registers programmed with the WIFI MAC: ESP32 Technical Reference Manual (Version 4.6), page 518.

All 3 boards return consistent data:

board1     0x1aec94    0xcb6e46e8
board2     0x9bec94    0xcb702434
board3     0xfc58bf     0x2593d268

The first 6 hex digits (example: 1aec94) are the higher 24 bits from EFUSE register EFUSE_BLK0_RDATA2_REG. The second group of 8 hex digits (example cb6e46e8) are the lower 32 bits from EFUSE register EFUSE_BLK0_RDATA1_REG.

Assuming a MAC address of 48 bits, or 12 hex digits, I did an OUI search (Organizationally Unique Identifier), not using the first 2 digits from the higher group. This search confirmed that these numbers really were the MAC.

An OUI search on ec:94:cb returns Espressif Inc as the company registering that sequence in April 2021. An OUI search on 58:bf:25 likewise returns Espressif Inc, registering that sequence in June 2021

The machine.unique_id() data can, painfully, be turned into those same 12 digit MAC addresses. Example (board1, for a MAC address of ec:94:cb:6e:46:e8)

b’\xec     = ec
\x94        = 94
\cb          = cb
n             = 6e  (from ASCII table, symbol to hex)
F             = 46  (from ASCII table, symbol to hex)
\e8          = e8

CODE1:
# Machine ID rr 3/17/22
# get unique id from DoIT ESP32 DEVKIT V1 boards MicroPython firmware v1.18

import machine

f_value = machine.unique_id()
print(f_value)

CODE2:
# ReadMemory2 3/21/22 rr
# read programmed WIFI MAC address from DoIT ESP32 DEVKIT V1 boards firmware v1.18
# see example MicroPython Documentation Release 1.18 page 393
# called 8.2.3 Accessing peripherals directly via registers# Absolute address information from ESP32 Technical Reference Manual Version 4.6, pages 515-518

from micropython import const
from machine import mem32

EFUSE_BLK0_RDATA1_REG = const(0X3FF5A004)
EFUSE_BLK0_RDATA2_REG = const(0X3FF5A008)

print(hex(mem32[EFUSE_BLK0_RDATA2_REG] & 0xffffffff)) # MAC upper 24 bits
print(hex(mem32[EFUSE_BLK0_RDATA1_REG] & 0xffffffff)) # MAC lower 32 bits