The ESP8266 is a very small and very cheap microcontroller and WiFi interface by Espressif Systems. It was originally intended as a turnkey WiFi module which spoke AT protocol via a UART, but it actually turns out to be a rather capable microcontroller in its own right.
It's based around a LX106 32-bit CPU (one of the Xtensa LX6 family) with 96kB of data RAM, 64 kB of code RAM, and an external NAND flash connected via SPI. A rather cunning demand-paging system allows the flash to be memory mapped, using 32kB of the code RAM for a cache. The ESP8285 is a very similar device except that it has an internal SPI flash that runs in a different mode.
The Fuzix port runs in multi-tasking mode with the root filesystem on the internal NAND flash. An SD card can be connected to the second SPI interface for further file storage and swap.
make TARGET=esp866 kernel diskimage
You need the xtensa-lx106-elf gcc toolchain --- install the
gcc-xtensa-lx106 package from Debian.
The base system assumes a typical ESP8266 configuration with a 26MHz peripheral clock and the CPU usually running at 80MHz. If you get weird serial speeds run esptool and set the peripheral clock in config.h to twice the clock it reports.
The flash mappings and clocking is managed by the hardware based upon the image header. These are set by the esptool when you flash the image. The '-ff' option sets the SPI flash frequency and the -fm the mode. 40 (Mhz) is a safe flash setting but most boards can do 80. The ESP8266 boards generally support 'qio' (the fastest option), some require 'dio' and the ESP8285 requires 'dout'. You can adjust these in the command or the make burn settings. If it fails try more conservative settings. Many of the bigger ESP-12 MCUs (often used for NodeMCU require dio).
Out of the box:
- /dev/hda is the NAND flash. The system is configured for a 2MB flash chip, which gives you a root filesystem of 1279kB.
- /dev/hdb is the SD card. This is only probed on startup --- you can't hot swap it.
Connect the SD card to the following pins:
NodeMCU pin GPIO pin SD card pin
-----------------------------------------
D5 14 SCK
D6 12 MISO
D7 13 MOSI
D2 4 CS
Remember to also connect the SD card's GND to any ESP8266 GND pin and Vcc to 3.3V. Not 5V, or it won't work (and that's likely to be a permanent change).
The console is UART0, and runs at 115200 baud.
Doing make -C Kernel/platform-esp8266 burn will flash the kernel onto the device
connected on /dev/ttyUSB0 with this command:
`esptool --port /dev/ttyUSB0 write_flash 0x00000 image.elf-0x00000.bin 0x10000 image.elf-0x10000.bin -ff 80m -fm dio'
Doing make -C Kernel/platform-esp8266 fburn will flash the filesystem onto
the device in the same manner.
Out of the box, Fuzix runs in swapless mode. This gives enough memory to run
most normal programs (you can use free to see how much you have left). If you
want more, you can enable swapping to the SD card.
To do this, create a 2048kB (4096 blocks) partition on the SD card. Then use
the swapon command to enable swap. You can see swap usage with free.
# fdisk -l
START END
Device Boot Head Sector Cylinder Head Sector Cylinder Type Sector count
/dev/hdb1 33 3 0 38 6 1 83 4096
/dev/hdb2 38 7 1 58 8 18 83 65536
# swapon /dev/hdb1 4096
# free
total used free
Mem: 160 56 104
Swap: 2048 0 2048
#
You can't turn swap off again.
You probably can swap to the NAND flash, but it's a terrible idea.
GPIO1 Serial TX } To the USB UART on the NodeMCU kits GPIO3 Serial RX }
GPIO4 SDcard CS } GPIO5 Second CS } GPIO12 MISO } SD card interface (note Arduino GPIO13 MOSI } tends to use GPIO15 not 4 but GPIO15 GPIO14 SCK } is also used during boot)
GPIO6-11 SPI Flash
GPIO0 Bootloader button GPIO2 Usually an on board LED, used for W5500 reset GPIO9/10 Used in QIO Flash mode, otherwise not used GPIO16 Deep sleep wakeup, not used
A0 Not used
3FFE8000-3FFFBFFF Data RAM
3FFE8000-3FFF7FFF User space
3FFF8000-3FFFBFFF Kernel
3FFFC000-3FFFFFFF ETS data RAM
3FFFC000-3FFFC713 Unused (move stacks and tmp buffers?)
3FFFC714-3FFFC733 Firmware flash structure we need to keep alive
3FFFC734-3FFFFFFF Buffers
40000000-4000FFFF Internal ROM (some routines usable)
40100000-40107FFF Instruction RAM (64K). Fast memory for programs
40100000 - Bootstrap (bottom - overwritten)
40100000-40107DFF - Userspace code
40107E00-40107FFF - NAND flash lowlevel functions
40108000-4010BFFF - Cache block #1 (used by us for userspace code)
4010C000-4010FFFF - Cache block #2 (used for SPI flash mapping)
40200000-402FFFFF SPI Flash (cacheable), only accessible as if it was iram
40200000 - Bootloader
40201000 - Kernel
40220000 - NAND flash fs
ESP8266 binaries are specific to this platform and won't run on any other ESP modules: the Xtensa architecture is very flexible and ABI compatibility is too hard. The binaries use the Fuzix tiny architecture and are limited to 64kB of data and 31.5kB of code. They're not relocatable.
The ESP8266's mask ROM contains many useful routines which can be used instead of libgcc, which reduces the binary size. These aren't documented, but you might find this ROM disassembly useful:
http://cholla.mmto.org/esp8266/bootrom/
There are many.
- someone needs to overhaul the SD SPI code who understands it.
- not all the ROM routines are hooked up to userland binaries.
- the tensilica asm could do with a clean up by someone who knows it better
...and probably others.
dg@cowlark.com did the original port.
Get gcc 10 and currentish binutils from the FSF mirrors and unpack them. Get the Debian source package from https://packages.debian.org/unstable/gcc-xtensa-lx106 Unpack it and apply the three patches from local-patches in the archive to the gcc you unpacked. Copy the xtensa-config.h from overlay/include over the one in gcc.
For binutils get https://packages.debian.org/unstable/binutils-xtensa-lx106 and copy overlay/bfd/xtensa-modules.c into the bfd directory of binutils. Copy the xtensa-config.h over the one in the binutils include directory.
% mkdir /opt/esp8266
% mkdir binutils
% cd binutils
% ../binutils-2.37/configure --prefix=/opt/esp8266 --target=xtensa-lx106-elf
% make
% make install
% PATH=/opt/esp8266/bin:$PATH
% mkdir gcc
% cd gcc
% ../gcc-10.3.0/configure --target=xtensa-lx106-elf --prefix=/opt/esp8266 --disable-decimal-float --disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath --disable-libquadmath-support --disable-libssp --disable-libstdcxx-pch --disable-libstdc++-v3 --disable-nls --disable-shared --disable-threads --disable-lts --enable-lto --enable-target-optspace --disable-_cxa_atexit --without-long-double-128 --disable-multilib --enable-cxx-flags=-fno-exceptions --with-gnu-as --with-gnu-ld --with-headers=no --without-newlib --without-included-gettext --enable-languages=c,c++
% make
% make install
You now have an ESP8266 compiler set.
- Use some of the ROM library routines that don't themselves meddle with static data. Make a kernel set and a user set (RBOOT has a good list) Note that we can't use many of them as they are not instruction fault aware.
- Move to 'parent runs first' - needs some tricky changes in the platform fork code (see the Z80 examples)
- Clean up the low level asm code - too much duplication, things saved that are not needed. Could do with a clean up by someone who speaks Tensilica LX106 properly.
- Can we autodetect and manage stuff like peripheral clocks ? (apparently it hides in the phy structures at the end of the flash?)
- Shared ROM libc
- XIP ROM app code ?
vim: set ts=4 sw=4 et