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255 lines
14 KiB
255 lines
14 KiB
ESP-LINK
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========
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[](https://gitter.im/jeelabs/esp-link?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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This firmware implements a transparent bridge between Wifi and serial using an ESP8266 module.
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It also provides support for flash-programming Arduino/AVR microcontrollers as well as
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LPC800-series ARM microcontrollers via the ESP8266.
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The firmware includes a tiny HTTP server based on
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[esphttpd](http://www.esp8266.com/viewforum.php?f=34)
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with a simple web interface, many thanks to Jeroen Domburg for making it available!
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Eye Candy
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---------
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These screen shots show the Wifi configuration page and the esp firmware's log
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<img width="45%" src="https://cloud.githubusercontent.com/assets/39480/8261425/6ca395a6-167f-11e5-8e92-77150371135a.png">
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<img width="45%" src="https://cloud.githubusercontent.com/assets/39480/8261426/6ca7f75e-167f-11e5-827d-9a1c582ad05d.png">
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<img width="45%" src="https://cloud.githubusercontent.com/assets/39480/8261427/6caf7326-167f-11e5-8085-bc8b20159b2b.png">
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Hardware info
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-------------
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This firmware is designed for esp8266 modules which have most ESP I/O pins available.
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The default connections are:
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- URXD: connect to TX of microcontroller
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- UTXD: connect to RX of microcontroller
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- GPIO12: connect to RESET of microcontroller
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- GPIO13: connect to ISP of LPC/ARM microcontroller (not used with Arduino/AVR)
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- GPIO0: optionally connect green "conn" LED to 3.3V (indicates wifi status)
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- GPIO2: optionally connect yellow "ser" LED to 3.3V (indicates serial activity)
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If you are using an FTDI connector, GPIO12 goes to DTR and GPIO13 goes to CTS.
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The GPIO pin assignments can be changed dynamicall in the web UI and are saved in flash.
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Initial flashing
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----------------
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(This is not necessary if you receive one of the jn-esp or esp-bridge modules.)
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If you want to simply flash the provided firmware binary, you can download the latest
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[release](https://github.com/jeelabs/esp-link/releases) and use your favorite
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ESP8266 flashing tool to flash the following:
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- `boot_v1.3(b3).bin` to 0x00000
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- `blank.bin` to 0x7e000
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- `user1.bin` to 0x01000
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Note that the firmware assumes a 512KB flash chip, which most of the esp-01 thru esp-11
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modules appear to have.
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Wifi configuration overview
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------------------
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For proper operation the end state the esp-link needs to arrive at is to have it
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join your pre-existing wifi network as a pure station.
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However, in order to get there the esp-link will start out as an access point and you'll have
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to join its network to configure it. The short version is:
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1. the esp-link creates a wifi access point
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2. your laptop joins as a station and you configure the esp-link wifi with your network info
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by pointing your browser at `http://192.168.4.1/`
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3. the esp-link joins your network while continuing to also be an access point ("AP+STA")
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4. the esp-link succeeds in connecting and shuts down its own access point
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5. if the esp-link looses your network it brings up its access point again
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LED indicators
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--------------
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Assuming appropriate hardware attached to GPIO pins, the green "conn" LED will show the wifi
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status as follows:
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- Very short flash once a second: not connected to a network and running as AP+STA
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- Very short flash once every two seconds: not connected to a network and running as AP-only
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- Even on/off at 1HZ: connected to your network but no IP address (waiting for DHCP)
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- Steady on with very short off every 3 seconds: connected to your network with an IP address
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(esp-link shuts down its AP after 15 seconds)
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The yellow "ser" LED will blink briefly every time serial data is sent or received by the esp-link.
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Wifi configuration details
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--------------------------
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After you have serially flashed the module it will create a wifi access point (AP) with an
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SSID of the form `ESP_012ABC` where 012ABC is a piece of the module's MAC address.
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Using a laptop, phone, or tablet connect to this SSID and then open a browser pointed at
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`http://192.168.4.1/`, you should then see the esp-link web site.
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Now configure the wifi. The desired configuration is for the esp-link to be a
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station on your local wifi network so you can communicate with it from all your computers.
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To make this happen, navigate to the wifi page and you should see the esp-link scan
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for available networks.
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If nothing happens verify that it is in AP+STA mode and not in AP-only mode (I need to fix this).
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You should then see a list of detected networks on the web page and you can select
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yours. Enter a password if your network is secure (recommended...) and hit the connect button.
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You should now see that the esp-link has connected to your network and it should show you
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its IP address. _Write it down_ (due to a bug you won't see it anymore after this) and then
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follow the provided link (you will have to switch your
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laptop, phone, or tablet back to your network before you can actually connect).
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At this point the esp-link will have switched to STA mode and be just a station on your
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wifi network. These settings are stored in flash and thereby remembered through resets and
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power cycles. They are also remembered when you flash new firmware. Only flashing `blank.bin`
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as indicated above will reset the wifi settings.
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There is a fail-safe, which is that after a reset or a configuration change, if the esp-link
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cannot connect to your network it will revert back to AP+STA mode after 15 seconds and thus
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both present its `ESP_012ABC`-style network and continue trying to reconnect to the requested network.
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You can then connect to the esp-link's AP and reconfigure the station part.
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Building the firmware
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---------------------
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The firmware has been built using the [esp-open-sdk](https://github.com/pfalcon/esp-open-sdk)
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on a Linux system. Create an esp8266 directory, install the esp-open-sdk into a sub-directory.
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Download the Espressif SDK (1.0.1) and also expand it into a sub-directory. Then clone
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this repository into a third sub-directory. This way the relative paths in the Makefile will work.
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If you choose a different directory structure look at the Makefile for the appropriate environment
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variables to define. (I have not used the esptool for flashing, so I don't know whether what's
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in the Makefile for that works or not.)
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In order to OTA-update the esp8266 you should `export ESP_HOSTNAME=...` with the hostname or
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IP address of your module.
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This project makes use of heatshrink, which is a git submodule. To fetch the code:
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```
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cd esp-link
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git submodule init
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git submodule update
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```
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Now, build the code: `make` in the top-level of esp-link.
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Flashing the firmware
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---------------------
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This firmware supports over-the-air (OTA) flashing, so you do not have to deal with serial
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flashing again after the initial one! The recommended way to flash is to use `make wiflash`
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if you are also building the firmware.
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If you are downloading firmware binaries use `./wiflash.sh`.
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`make wiflash` assumes that you set `ESP_HOSTNAME` to the hostname or IP address of your esp-link.
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The flashing, restart, and re-associating with your wireless network takes about 15 seconds
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and is fully automatic. The 512KB flash are divided into two 236KB partitions allowing for new
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code to be uploaded into one partition while running from the other. This is the official
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OTA upgrade method supported by the SDK, except that the firmware is POSTed to the module
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using curl as opposed to having the module download it from a cloud server.
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If you are downloading the binary versions of the firmware (links forthcoming) you need to have
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both `user1.bin` and `user2.bin` handy and run `wiflash.sh <esp-hostname> user1.bin user2.bin`.
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This will query the esp-link for which file it needs, upload the file, and then reconnect to
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ensure all is well.
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Note that when you flash the firmware the wifi settings are all preserved so the esp-link should
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reconnect to your network within a few seconds and the whole flashing process should take 15-30
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from beginning to end. If you need to clear the wifi settings you need to reflash the `blank.bin`
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using the serial port.
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Serial bridge and connections to Arduino, AVR, ARM, LPC microcontrollers
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------------------------------------------------------------------------
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In order to connect through the esp-link to a microcontroller use port 23. For example,
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on linux you can use `nc esp-hostname 23` or `telnet esp-hostname 23`.
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You can reprogram an Arduino / AVR microcontroller by pointing avrdude at port 23. Instead of
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specifying a serial port of the form /dev/ttyUSB0 use `net:esp-hostname:23` (where `esp-hostname`
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is either the hostname of your esp-link or its IP address). The esp-link detects that avrdude
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starts its connection with a flash synchronization sequence and sends a reset to the AVR
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microcontroller so it can switch into flash programming mode.
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You can reprogram NXP's LPC800-series ARM processors as well by pointing your programmer
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similarly at the esp-link's port 23. For example, if you are using
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https://github.com/jeelabs/embello/tree/master/tools/uploader a command line like
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`uploader -s -w esp-link:23 build/firmware.bin` should do the trick.
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The way it works is that esp-link detects that the uploader starts its connection with the
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flash synchronization sequence `?\r\n` and issues the appropriate "ISP" and reset sequence
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to the microcontroller to start the flash programming.
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Note that multiple connections to port 23 can be made simultaneously. The esp-link will
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intermix characters received on all these connections onto the serial TX and it will
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broadcast incoming characters from the serial RX to all connections. Use with caution...
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Flash layout
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------------
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The flash layout dictated by the bootloader is the following (all this assumes a 512KB flash chip
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and is documented in Espressif's `99C-ESP8266__OTA_Upgrade__EN_v1.5.pdf`):
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- @0x00000 4KB bootloader
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- @0x01000 236KB partition1
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- @0x3E000 16KB user parameters
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- @0x40000 4KB unused
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- @0x41000 236KB partition2
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- @0x4E000 16KB system parameters
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What this means is that we can flash just about anything into partition1 or partition2 as long
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as it doesn't take more than 236KB and has the right format that the boot loader understands.
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We can't mess with the first 4KB nor the last 16KB of the flash.
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I have not investigated how badly the user
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parameters and unused sections can be abused, that's for the moment where I get desperate looking
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for a few more KB...
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Now how does a code partition break down? that is reflected in the following definition found in
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the loader scripts:
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```
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dram0_0_seg : org = 0x3FFE8000, len = 0x14000
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iram1_0_seg : org = 0x40100000, len = 0x8000
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irom0_0_seg : org = 0x40201010, len = 0x2B000
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```
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This means that 80KB (0x14000) are reserved for "dram0_0", 32KB (0x8000) for "iram1_0" and
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172KB (0x2B000) are reserved for irom0_0. The segments are used as follows:
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- dram0_0 is the data RAM and some of that gets initialized at boot time from flash (static variable initialization)
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- iram1_0 is the instruction RAM and all of that gets loaded at boot time from flash
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- irom0_0 is the instruction cache which gets loaded on-demand from flash (all functions
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with the `ICACHE_FLASH_ATTR` attribute go there)
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You might notice that 80KB+32KB+172KB is more than 236KB and that's because not the entire dram0_0
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segment needs to be loaded from flash, only the portion with statically initialized data.
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You might also notice that while iram1_0 is as large as the chip's instruction RAM (at least
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according to the info I've seen) the size of the irom0_0 segment is smaller than it could be,
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since it's really not bounded by any limitation of the processor (it simply backs the cache).
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When putting the OTA flash process together I ran into loader issues, namely, while I was having
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relatively little initialized data and also not 32KB of iram1_0 instructions I was overflowing
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the allotted 172KB of irom0_0. To fix the problem the build process modifies the loader scripts
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(see the `build/eagle.esphttpd1.v6.ld` target in the Makefile) to increase the irom0_0 segment
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to 224KB (a somewhat arbitrary value). This doesn't mean that there will be 224KB of irom0_0
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in flash, it just means that that's the maximum the linker will put there without giving an error.
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In the end what has to fit into the magic 236KB is the sum of the actual initialized data,
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the actually used iram1_0 segment, and the irom0_0 segment.
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In addition, the dram0_0 and iram1_0 segments can't exceed what's specified
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in the loader script 'cause those are the limitations of the processor.
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Now that you hopefully understand the above you can understand the line printed by the Makefile
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when linking the firmware, which looks something like:
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```
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** user1.bin uses 218592 bytes of 241664 available
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```
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Here 241664 is 236KB and 218592 is the size of what's getting flashed, so you can tell that you have
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another 22KB to spend (modulo some 4KB flash segment rounding).
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(Note that user2.bin has exactly the same size, so the Makefile doesn't print its info.)
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The Makefile also prints a few more details:
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```
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ls -ls eagle*bin
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4 -rwxrwxr-x 1 tve tve 2652 May 24 10:12 eagle.app.v6.data.bin
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176 -rwxrwxr-x 1 tve tve 179732 May 24 10:12 eagle.app.v6.irom0text.bin
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8 -rwxrwxr-x 1 tve tve 5732 May 24 10:12 eagle.app.v6.rodata.bin
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32 -rwxrwxr-x 1 tve tve 30402 May 24 10:12 eagle.app.v6.text.bin
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```
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This says that we have 179732 bytes of irom0_0, we have 5732+2652 bytes of dram0_0 (read-only data
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plus initialized read-write data), and we have 30402 bytes of iram1_0.
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There's an additional twist to all this for the espfs "file system" that esphttpd uses.
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The data for this is loaded at the end of irom0_0 and is called espfs.
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The Makefile modifies the loader script to place the espfs at the start of irom0_0 and
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ensure that it's 32-bit aligned. The size of the espfs is shown here:
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```
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4026be14 g .irom0.text 00000000 _binary_espfs_img_end
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40269e98 g .irom0.text 00000000 _binary_espfs_img_start
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00001f7c g *ABS* 00000000 _binary_espfs_img_size
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```
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Namely, 0x1f7c = 8060 bytes.
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