8ffe41b7df
Provides a transparently accessible additional block of RAM of 128K to
8MB by using an external SPI SRAM. This memory is managed using the UMM
memory manager and can be used by the core as if it were internal RAM
(albeit much slower to read or write).
The use case would be for things which are quite large but not
particularly frequently used or compute intensive. For example, the SSL
buffers of 16K++ are a good fit for this, as are the contents of Strings
(both to avoid main heap fragmentation as well as allowing Strings of
>30KB).
A fully associative LRU cache is used to limit the SPI bus bottleneck,
and background writeback is supported.
Uses a define in boards.txt to enable. If this value is not defined,
then the entire VM routines should not be linked in to user apps
so there should be no space penalty w/o it.
UMM `malloc` and `new` are modified to support internal and external
heap regions. By default, everything comes from the standard heap, but
a call to `ESP.setExternalHeap()` before the allocation (followed by a
call to `ESP.resetHeap()` will make the allocation come from external
RAM. See the `virtualmem.ino` example for use.
If there is no external RAM installed, the `setExternalHeap` call is a
no-op.
The String and BearSSL libraries have been modified to use this external
RAM automatically.
Theory of Operation:
The Xtensa core generates a hardware exception (unrelated to C++
exceptions) when an address that's defined as invalid for load or store.
The XTOS ROM routines capture the machine state and call a standard C
exception handler routine (or the default one which resets the system).
We hook into this exception callback and decode the EXCVADDR (the
address being accessed) and use the exception PC to read out the
faulting instruction. We decode that instruction and simulate it's
behavior (i.e. either loading or storing some data to a
register/external memory) and then return to the calling application.
We use the hardware SPI interface to talk to an external SRAM/PSRAM,
and implement a simple cache to minimize the amount of times we need
to go out over the (slow) SPI bus. The SPI is set up in a DIO mode
which uses no more pins than normal SPI, but provides for ~2X faster
transfers. SIO mode is also supported.
NOTE: This works fine for processor accesses, but cannot be used by
any of the peripherals' DMA. For that, we'd need a real MMU.
Hardware Configuration (only use 3.3V compatible SRAMs!):
SPI byte-addressible SRAM/PSRAM: 23LC1024 or smaller
CS -> GPIO15
SCK -> GPIO14
MOSI -> GPIO13
MISO -> GPIO12
(note these are GPIO numbers, not the Arduino Dxx pin names. Refer
to your ESP8266 board schematic for the mapping of GPIO to pin.)
Higher density PSRAM (ESP-PSRAM64H/etc.) should work as well, but
I'm still waiting on my chips so haven't done any testing. Biggest
concern is their command set and functionality in DIO mode. If DIO
mode isn't supported, then a fallback to SIO is possible.
This PR originated with code from @pvvx's esp8266web server at
https://github.com/pvvx/esp8266web (licensed in the public domain)
but doesn't resemble it much any more. Thanks, @pvvx!
Keep a list of the last 8 lines in RAM (~.5KB of RAM) and use that to
speed up things like memcpys and other operations where the source and
destination addresses are inside VM RAM.
A custom set of SPI routines is used in the VM system for speed and code
size (and because the core cannot be dependent on a library).
Because UMM manages RAM in 8 byte chunks, attempting to manage the
entire 1M available space on a 1M PSRAM causes the block IDs to
overflow, crashing things at some point. Limit the UMM allocation to
only 256K in this case. The remaining space can manually be assigned to
buffers/etc. managed by the application, not malloc()/free().
Arduino core for ESP8266 WiFi chip
Quick links
Arduino on ESP8266
This project brings support for the ESP8266 chip to the Arduino environment. It lets you write sketches, using familiar Arduino functions and libraries, and run them directly on ESP8266, with no external microcontroller required.
ESP8266 Arduino core comes with libraries to communicate over WiFi using TCP and UDP, set up HTTP, mDNS, SSDP, and DNS servers, do OTA updates, use a file system in flash memory, and work with SD cards, servos, SPI and I2C peripherals.
Contents
- Installing options:
- Documentation
- Issues and support
- Contributing
- License and credits
Installing with Boards Manager
Starting with 1.6.4, Arduino allows installation of third-party platform packages using Boards Manager. We have packages available for Windows, Mac OS, and Linux (32 and 64 bit).
- Install the current upstream Arduino IDE at the 1.8.9 level or later. The current version is on the Arduino website.
- Start Arduino and open the Preferences window.
- Enter
https://arduino.esp8266.com/stable/package_esp8266com_index.jsoninto the File>Preferences>Additional Boards Manager URLs field of the Arduino IDE. You can add multiple URLs, separating them with commas. - Open Boards Manager from Tools > Board menu and install esp8266 platform (and don't forget to select your ESP8266 board from Tools > Board menu after installation).
Latest release 
Boards manager link: https://arduino.esp8266.com/stable/package_esp8266com_index.json
Documentation: https://arduino-esp8266.readthedocs.io/en/2.7.4_a/
Using git version
Also known as latest git or master branch.
- Install the current upstream Arduino IDE at the 1.8 level or later. The current version is on the Arduino website.
- Follow the instructions in the documentation.
Using PlatformIO
PlatformIO is an open source ecosystem for IoT development with a cross-platform build system, a library manager, and full support for Espressif (ESP8266) development. It works on the following popular host operating systems: macOS, Windows, Linux 32/64, and Linux ARM (like Raspberry Pi, BeagleBone, CubieBoard).
- What is PlatformIO?
- PlatformIO IDE
- PlatformIO Core (command line tool)
- Advanced usage - custom settings, uploading to SPIFFS, Over-the-Air (OTA), staging version
- Integration with Cloud and Standalone IDEs - Cloud9, Codeanywhere, Eclipse Che (Codenvy), Atom, CLion, Eclipse, Emacs, NetBeans, Qt Creator, Sublime Text, VIM, Visual Studio, and VSCode
- Project Examples
Building with make
makeEspArduino is a generic makefile for any ESP8266 Arduino project. Using make instead of the Arduino IDE makes it easier to do automated and production builds.
Documentation
Documentation for latest development version: https://arduino-esp8266.readthedocs.io/en/latest/
Issues and support
ESP8266 Community Forum is a well-established community for questions and answers about Arduino for ESP8266. Stackoverflow is also an alternative. If you need help, have a "How do I..." type question, have a problem with a 3rd party library not hosted in this repo, or just want to discuss how to approach a problem, please ask there.
If you find the forum useful, please consider supporting it with a donation.
If you encounter an issue which you think is a bug in the ESP8266 Arduino Core or the associated libraries, or if you want to propose an enhancement, you are welcome to submit it here on Github: https://github.com/esp8266/Arduino/issues.
Please provide as much context as possible, as well as the information requested in the issue template:
- ESP8266 Arduino core version which you are using (you can check it in Boards Manager)
- your sketch code; please wrap it into a code block, see Github markdown manual
- when encountering an issue that happens at run time, attach the serial output. Wrap it into a code block, just like the code.
- for issues that happen at compile time, enable verbose compiler output in the IDE preferences, and attach that output (also inside a code block)
- ESP8266 development board model
- IDE settings (board choice, flash size)
- etc
Contributing
For minor fixes of code and documentation, please go ahead and submit a pull request. A gentle introduction to the process can be found here.
Check out the list of issues that are easy to fix — easy issues pending. Working on them is a great way to move the project forward.
Larger changes (rewriting parts of existing code from scratch, adding new functions to the core, adding new libraries) should generally be discussed by opening an issue first. PRs with such changes require testing and approval.
Feature branches with lots of small commits (especially titled "oops", "fix typo", "forgot to add file", etc.) should be squashed before opening a pull request. At the same time, please refrain from putting multiple unrelated changes into a single pull request.
License and credits
Arduino IDE is developed and maintained by the Arduino team. The IDE is licensed under GPL.
ESP8266 core includes an xtensa gcc toolchain, which is also under GPL.
Esptool.py was initially created by Fredrik Ahlberg (@themadinventor, @kongo), and is currently maintained by Angus Gratton (@projectgus) under GPL 2.0 license.
Espressif's NONOS SDK included in this build is under Espressif MIT License.
ESP8266 core files are licensed under LGPL.
SPI Flash File System (SPIFFS) written by Peter Andersson is used in this project. It is distributed under the MIT license.
umm_malloc memory management library written by Ralph Hempel is used in this project. It is distributed under the MIT license.
SoftwareSerial library and examples written by Peter Lerup. Distributed under LGPL 2.1.
BearSSL library written by Thomas Pornin, built from https://github.com/earlephilhower/bearssl-esp8266, is used in this project. It is distributed under the MIT License.
LittleFS library written by ARM Limited and released under the BSD 3-clause license.
uzlib library written and (c) 2014-2018 Paul Sokolovsky, licensed under the ZLib license (https://www.zlib.net/zlib_license.html). uzlib is based on: tinf library by Joergen Ibsen (Deflate decompression); Deflate Static Huffman tree routines by Simon Tatham; LZ77 compressor by Paul Sokolovsky; with library integrated and maintained by Paul Sokolovsky.
Other useful links
Serial Monitor Arduino IDE plugin Original discussion here, quick download there.