Can I have the XS compiler on the MCU too?

[rkompass]

I just discovered moddable. I installed everything for ESP32 and it went fine. Thank you and congratulations.
A simple benchmark (adding up integers 1,2,..,1000000) showed that the XS interpreter is fast.
It seemed to be 3 times as fast as the MicroPython interpreter for the same device - impressing!
I have some experience with MP (MicroPython) by now and might do a more detailed comparison perhaps.

The big difference with MP I notice is:
Every time a new version of my JS program is to be run with mcconfig -d -m -p esp32/nodemcu
it requires a new bytecode interpreter to be set up and all three of:

• 18256 bytes of bootloader (??),
• 407488 bytes of XS bytecode interpreter (my guess) and
• 3072 bytes of bytecode (apparently)

have to be flashed onto the board.

With MP I put the python code onto the board and let it execute (MP and bootloader are flashed once, or when the MP version changes). I'm used to this style and like it.
However I understand that from a professional point of view it seems sufficient to have just the bootloader, interpreter and bytecode and flash them together (with MP a recurring question is how to build it without the compiler, which is told to ~40kB smaller).

In the docs (XS7-TC-39) I found:

In the traditional runtime model, the two parts are of course chained. For embedded development, the XS compiler runs on a PC and the resulting byte code is flashed into ROM where it is executed.

In fact, most embedded devices cannot afford to parse, scope and code modules or scripts themselves, so that part of XS is often absent, which saves some ROM at the cost of eval, new Function and new Generator.

So it seems that some embedded devices allow for having the full XS functionality, perhaps even a JS REPL.?.

• Would this include the ESP32?
  Is there an example or a guide how to flash such a complete version of XS onto a board/device? To have sort of a Micro-Node.js REPL?
• Is there an option to have a quite complete XS interpreter on the device that allows for just flashing bytecode?
  With a search here I just learnt that this latter functionality is provided through mods - sorry for asking.

Thank you,
Raul

[phoddie]

Welcome!

So it seems that some embedded devices allow for having the full XS functionality, perhaps even a JS REPL.?.

Yup. You can run eval as usual, if you like. A bunch of details about that are in the my blog post Compiling JavaScript on Embedded Devices. If you have questions beyond that, please let me know.

[rkompass]

Thank you. Very nice blog post. Addresses exactly what I wanted to do: Inspect the XS machine from inside.

Unfortunately the instructions given there to build the REPL failed here:

/home/raul/Moddable/moddable/build/tmp/esp32/nodemcu/release/repl/xsProj-esp32/main/main.c: In function 'app_main':
/home/raul/Moddable/moddable/build/tmp/esp32/nodemcu/release/repl/xsProj-esp32/main/main.c:243:32: error: 'CONFIG_ESP_CONSOLE_UART_BAUDRATE' undeclared (first use in this function); did you mean 'CONFIG_ESP_CONSOLE_UART_NONE'?
  243 |         uartConfig.baud_rate = CONFIG_ESP_CONSOLE_UART_BAUDRATE;
      |                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                                CONFIG_ESP_CONSOLE_UART_NONE
/home/raul/Moddable/moddable/build/tmp/esp32/nodemcu/release/repl/xsProj-esp32/main/main.c:243:32: note: each undeclared identifier is reported only once for each function it app

Maybe due to some changes in the ESP32 SDK?

[rkompass]

Solved: I included

#ifndef CONFIG_ESP_CONSOLE_UART_BAUDRATE
	#define CONFIG_ESP_CONSOLE_UART_BAUDRATE 115200
#endif

after the definition of DEBUGGER_SPEED in moddable/build/devices/esp32/xsProj-esp32/main/main.c
and everything built fine after that.

You might update the sources perhaps. I'm not too familiar with PRs, sorry. This is why I leave that to you or someone else.

[rkompass]

Now a next question: Can the REPL setup be a host? I.e. be updated with new mods?
I suppose that would not be easy as the USB serial is now given to the REPL.
Which works fine, btw. With the $MODDABLE/examples/js/repl build I may connect to a newly plugged in ESP32 device by a simple screen /dev/ttyUSB0 115200. No greeting banner though, no Ctrl-C, no Ctrl-D, no C Ctrl-E like I'm used to from Micropython. :-|
But very very nice anyway.

[phoddie]

Regarding CONFIG_ESP_CONSOLE_UART_BAUDRATE, that constant does come from the ESP-IDF side of the build. I just built the REPL here using the recommended ESP-IDF version (v5.3.1) without errors. Here's the build line I used. Perhaps you did something different or are using a different ESP-IDF version?

cd $MODDABLE/examples/js/repl
mcconfig -d -m -p esp32/moddable_two

Can the REPL setup be a host? I.e. be updated with new mods?

All apps are a host – the capabilities of hosts vary broadly. The REPL in the Moddable SDK repository does support mods. That's enabled in its manifest:

	"defines": {
		"XS_MODS": 1
	},

You can build, install, and launch mods using mcrun after you've installed the REPL with mcconfig.

[rkompass]

Your above build command is different from that recommended in your linked previous eval blog post, where it was
mcconfig -m -p esp32. No debug switch there.
Here, with the debug switch set it also compiles nicely. Without that switch (as recommended in the blog), i.e. with mcconfig -m -p esp32/moddable_two it gives the same error. Whether the target is moddable-two or nodemcu does not matter.

When the target that was compiled with the debug switch runs, I cannot contact it whith the screen command.
It shows repeatedly:

rst:0xc (SW_CPU_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0030,len:428
ho 0 tail 12 room 4
load:0x40078000,len:14520
ho 0 tail 12 room 4
load:0x40080400,len:4
load:0x40080404,len:3204
entry 0x40080560
S�*��Zm�U�U��������[

and I can not enter commands.
I also apparently can not use the LOG window of xsbug, as that is not meant to be a terminal. Please correct me if I'm wrong.
So I'm forced to compile as release, it seems. And the above solution, or something equivalent, but more general, seems to be needed.

You can build, install, and launch mods using mcrun after you've installed the REPL with mcconfig.

Not sure whether that still is true for release builds. But if, it would be fantastic.