Electronics: ESP8266 examples

iPhone switched OFF and ON, connected to power, different iPhone
DHCP timeout 2->10 minutes
Auto IP works with iPhone, assigns IP 169.254.27.79. At same time, MacBook connects via wifi to same iPhone, gets IP 172.20.10.3, can ping esp
Android phones (tried 2) works, esp gets IP 192.168.43.118, MacBook gets 192.168.43.5, can ping esp
AutoIP with android phone, assigns DHCP IP 192.168.43.118 but after 2-6 failed tries, still does not use autoIP

How to switch AutoIP ON: make menuconfig: component—>LWIP—>enable IPV4 link local addressing

How to change DHCP timeout: make menuconfig: component—>config—>tcpip adapter—>IP address lost timer interval

Final approach for now: #3

Autoip approach did not work for further examples that required connection with internet

Bought new SIM to put in an android phone. That is working fine.

nvs, tcp-adapter, wifi ON

5. softAP example: worked without any problem

Protocols folder

Using protcol_examples_common.h and connect.c (example_connect/disconnect) for all examples in this folder

6. httprequest example

in addition to nvs, tcp-adapter, wifi ON, creating a socket connection using 'addressinfo', then send a GET request and receive response (full page from example.com)

main functions: get_task(), getaddreinfo()

7. httpserver example - simple

esp connected to android phone in station mode with IP 192.168.43.118 and becomes a server
laptop connected to same phone with IP 192.168.43.5 and becomes a client
Tried GET, PUT and POST
Chrome browser can

send GET request in URL
send query string in URL
show response body in main page
show request/response headers in browser (view->developer->inspect elements->network, re-send request)

Curl can

send GET, PUT and POST (and probably others)
can even send a file with POST and receive response in another file
may be able to send/show all request / response parameters
https://curl.haxx.se/docs/httpscripting.html

Modheader can (chrome plugin)

Add request / response headers to a particular URL

Restman can (chrome plugin)

send GET, PUT and POST with parameters
show response along with headers etc.
not sure how to send file in POST

8. httpserver example - persistent socket

http_req_t structure in esp_http_server.h
use of user_ctx to maintain and show visitor count
use of sess_ctx to send any number and accumulate it
use of local pointers to update value stored in global pointers like user_ctx and sess_ctx
All 3 (GET, PUT and POST) add 1 to visitor count & start a session if sess_ctx is NULL
Once sess_ctx is not NULL, the session can only be terminated by calling 'free' function. In this case, it gets called when webserver and hence the socket is closed
POST allows user to send a number that is added to sess_ctx
GET shows the current value of sess_ctx
PUT allows user to send a number, sess_ctx value is reset to that value

9. httpserver example - advanced tests

read esp_http_server.h (to understand get/set sess_ctx, get/set transport_ctx, get_global_user_ctx, get_global_transport_ctx, sess_trigger_close, sess_update_lru_counter)
8 handlers doing simple things
printing remaining heap
using httpd_queue_work
async_get_handler not working properly

10. esp_http_client_example

read esp_http_client.h
additional methods PATCH, DELETE, HEAD
EAGAIN message/error
Authentication types: basic v digest
Certification: SSL (confirms identity of server & encrypts data), PEM file
Redirection requests: absolute v relative (not full path but only page), make source relative, not destination
httpbin.org

11. https_request_example_main

basically to establish a secure connection SSL/TLS
esp_tls.h
simply using the wrapper API in file above
https_mbedtls_example_main: using esp_tls_mbedtls.h, complex API, lots of functions

12. openssl demo example

ssl.h
hosting structure with in-addr = 32 bit int to store IP address
get host by name
create ssl context (v1.1)
verify ssl context (verify none)
create socket
bind socket to local port (9999)
connect socket to remote server (IP, port 443)
create SSL
connect SSL to socket
check heap size / stack depth
send request to SSL (write)
read response

13. openssl client example (different points from demo)

extra certificates (ca, server, client - pem files and keys)
different version while creating context (v1.2)
load certificates and keys to context
verify ssl context (verify peer)
when run, client-server connected, server (laptop) showed request received but client could not get a response back

14. open ssl server example (different points)

after create context and socket, listen (instead of connect)
create ssl, then accept (server socket accept client)
connect ssl with new (client) socket
ssl accept (ssl server accept client)
write/read
same as client example, server could not get a response back from client (laptop)

15. sockets/tcp client & server example

using standard sockets.h
using python script to create server/client (on the other end of esp)
port is important, 50000 did not work, 3333 worked
BCD socket (link)

16. udp client example

destinationAddress = server’s
create socket with SOCK_DGRAM (datagram)
another while (1)
sendto (sock, payload, destAddr)
recvfrom (sock, buf, sourceAddr (blank)): you get data & sourceAddr
no 3 way handshake

17. udp server example

destAddr: INADDR_ANY (same as tcp)
create socket
bind socket and destAddr
another while(1)
recvfrom(sock, buf, sourceAddr (blank)): you get data & sourceAddr
sendto (sock, buf, sourceAddr)

18. udp multicast example: lots of new APIs, not clear

19. COAP

client, server
machine to machine
UDP based
methods similar to http

20. Multicast DNS (mdns)

resolves hostname to IP address within small (local) network that does not have a dedicated DNS
designed to enable simple, constrained devices to join the IoT even through constrained networks with low bandwidth and low availability
generally used for machine-to-machine (M2M) applications such as smart energy and building automation
app_main

mdns example task
generate hostname
initialise mdns
mdns print results
query mdns service
query mdns host
initialise button
while (1) check button, mdns example task

21. SNTP (simple network time protocol)

synchronizes system time with official world time / coordinated universal time
simpler (needs fewer algorithms) than NTP (network time protocol) but less accurate
not used much if processing power enough to run NTP
UDP port 123, TZ for India is Asia/Kolkata (not working), UTC-5:30 worked
app_main

sntp example task
initialise sntp
obtain time

22. MQTT (IBM MQ telemetry transport)

Useful links: internetofthingsagenda, espressif
Light weight IOT messaging, publish-subscribe architecture
client (pub) --> broker --> client (sub)
you subscribe to topics, if you publish topic gets created (if does not exist)
if broker->pub is broken, cached msg sent to all subs
if broker->sub is broken, values buffered & sent when back online
port 1883 (non encrypted), 8883 (encrypted)
client side certificates are also verified during handshake
connection-->authentication-->communication-->termination
2 byte fixed header+variable length optional header+256MB payload+QoS level
BLOBs - binary large objects
mqtt://mqtt.eclipse.org
graceful shutdown, easy reconnect
MQTT tcp client example

events: connected, published, subscribed, unsubscribed, disconnected
if data present with broker, no subscribe event called, direct data event
make erase_flash to get rid of prev data
test1: subscribe to qos0 only: print event_sub
test2: subscribe to qos1 only: event sub+event data (previously kept with broker, end less loop, msg id different every time). topic+event: unique msg id; topic / event change: msg id change
test3: qos0 sub & unsub: event_sub (diff msg ids)
test4: qos1 sub & unsub: event_sub, event_data, event_unsub (all diff msg ids)
test 5: qos0 sub, publish within event sub body; event_sub, event_data
test6: no prev data stored with broker in case of qos0
test7: qos0-sub, publish, unsub: event_sub, event_unsub (no data event!) unsub happens before data!
test8: qos0 pub-sub, qos1 sub-unsub: no data for qos0 unless you publish 'within sub event'. event_sub for qos0, event_data for qos1, event_unsub for qos1
test9: qos0 sub (publish within sub), qos1 sub-unsub: event_sub qos0, event_data qos1, event_unsub qos1, event_data qos0 (comes last event when published much earlier! priority less than qos1?)

MQTT webserver example

same code, only config for WS instead of TCP

MQTT webserver secure example

certificate of broker procured and added in config

MQTT on SSL example

same as WSS

MQTT SSL mutual auth example

additional client certificate with pem file & key
url hardcoded in config struct
used eclipse's mosquitto

22. SPIFFS - SPI flash file system (link). Various inbuilt C functions to handle files - great! stdio.h

Tested with Increased storage partition to (almost) maximum memory available in esp flash. partition tables

24. SoftAP provisioning example

About creating ‘provision’ (like electrical/plumbing) to update something (like wifi ssid/pwd in this case) while device is active (doing it’s main job)
Components

protocomm: manages secure session (app_prov.h/.c): can work over wifi (softap+httpd), BLE and console
protobuf: google’s protocol for serialised data transfer of structures
wifi provisoning: exchange of userid/pwd (wifi_init_sta/connect/mode)

Flow
- app_main
- app_prov.h
Running experience
- install google’s protobuf
- copied 1 missing file (wifi_scan.py) in sdk\tools\esp_prov\prov\
- updated 1 outdated file (security1.py) in sdk\tools\esp_prov\security\
- laptop and esp connect to each other and are also able to exchange data but does not work beyond a point
- keeps saying ‘connecting’, does not say ‘connected’ and does not proceed to close softap etc.
- system_events are not happening, no way to trigger system events from user code
- latest SDK/example code available on GitHub seems to be different from ours (downloaded 2 months ago)
Custom config: extra config / end-point in protocomm

25. System folder examples

Console
- components
- app_main
- Runs fine
- Reading: VFS
OTA

Reading: partition tables (link)

single factory app, no OTA: nvs, phy-init, factory (bootloader will run this by default)
nvs, otadata, phy_init, ota_0, ota_1 (bootloader will read otadata to know which app to run; if empty, will run 1st 'app' partition (ota_0/factory/test_app)
nvs (size 0x4000 or 0x2000) is for working data, can create extra 'data' partitions for storage like SPIFFS
1st app partition is starting at 0x10000 (64kB) in both default cases
app should be in integrated 1M partition - not clear

Reading: bootloader (link)

Bootloader is at 0x1000
it can update newer SDK code but not older
With old code, keep bootloader copy also!!
so don't upload (flash) ESP-IDF unless the code (forumware) is also updated and tested and can be uploaded (flashed) along with

ESP-IDF versions link
OTA links: main link having esp_ota_ops.h, link related to https
App rollback needs some thinking specially related to versioning & inability of bootloader to update older versions
simple_ota_example

read_me & ota_workflow.png is good

Running experience

Error1: hostname / common name not valid, certificate cannot be verified. While creating cert pem key, give hostname = IP address of server (laptop).
Error2: E (3220) esp-tls-mbedtls: mbedtls_ssl_handshake returned -0x2700
I (3223) esp-tls-mbedtls: Failed to verify peer certificate!
I (3226) esp-tls-mbedtls: verification info: ! The certificate Common Name (CN) does not match with the expected CN
! The certificate is not
E (3247) esp-tls: Failed to open new connection
E (3255) TRANS_SSL: Failed to open a new connection
E (3267) HTTP_CLIENT: Connection failed, sock < 0
E (3272) esp_https_ota: Failed to open HTTP connection: 28674
E (3281) simple_ota_example: Firmware Upgrades Failed
Sometimes returned 0x4c (instead of 0x2700)
Links studied: link1, link2
Worked when retried, working but still this error appears

E (13685) esp-tls-mbedtls: read error :-76:

E (13687) TRANS_SSL: esp_tls_conn_read error, errno=Socket is not connected

Electronics

Monday, 23 August 2021

ESP8266 examples

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