Hello,

I want to run some very small scripts an a PIC32 microcontroller to extend it's functionality without changing the firmware. I found Squirrel and it looks very good to me. Especially I like the c similarity of the language.
Does anyone have experience in running Squirrel on an embedded system? I would use the XC32 Compiler from Microchip (http://ww1.microchip.com/downloads/en/DeviceDoc/50001686J.pdf). It is based on the gcc. I think it should work, or are there any known issues?

Thanks for all kinds of informations
Florian

Hello,

I would like to ask some questions about how squirrel can be used on microcontrollers:

Could you tell me what are the dependencies of squirrel?
-What C++ dialect it was written in? (Cpp11?)
-Does it use external libraries or STL? (STL is rarely available)
-Does it use OS APIs?

Best regards,
Quentis

the most serious issue usually is indeed the use of VARGS and vsnprintf and co, those quite often are not properly supported by MCU libraries.
Unfortunately, those are also the ones pumping up footprint a lot (which is why they're often not fully supported)

Some additional (but quite standard) libs add up when using sqstdlib (e.g. system, time, file stream handling and a few others), but those are easy to circumvent or omit.

The makefiles are straigtforward, you can compile squirrel simply by adding all source files to a project and there you go.

(BTW: Add Metroworks compiler to the list)

Some other hints:
- After loading a script and running it, when you do not intend to completely run it again but only want to call functions from it - DELETE THE LOADED SCRIPT (After the first run it's never used again, so you can free that memory chunk).
- Compile with NO_GARBAGECOLLECTOR. You really want so save that extra memory and cpu power on a MCU
- Amend sqconfig.h properly to fit your needs, you could also easily replace the printf stuff with own functions here, if necessary
- write your own memory allocation and management. Squirrel tends to use certain block sizes a damn lot. Also,usually "realloc" is THE bottleneck when it comes to performance. Squirrel for example does a lot of reallocs simply doubling the block size (which again are quite often powers of 2). You can optimize hell of a lot here...

Well, and as Alberto already said, you don't want the squirrel compiler if you can run precompiled scripts and never need to compile runtime (note that this impacts sqstdlib, too, see "dofile", for example)

With some effort (somewhere between "does run out of the box" and a few days) you should be able to get a decent system up and running.

Hi,

sorry for reviving an old post!

I did the porting on a PIC32 microcontroller; it works quite well, but the RAM usage is high.
I have 128 KBytes of RAM, 120 free; when I open the VM they drop to 50-60 KB, and with very few bingings yet.
Is there a way to reduce the RAM usage ? I think it's copying much data from flash to RAM, which if avoided could make an huge difference.
Is it possible ?

Ciao

Massimo

Squirrel itself does not target a specific platform, hence no improvements in this area. You will have to port that on your own.

I can tell, any micro will have to have decent RAM amounts, Squirrel code and data assumes von Neumann architecture (while on the C++ side of course Harvard will do, been there, did that)
Running bytecode directly from Flash without much RAM will be a tough approach, as squirrels structure bases on creating and initializing objects in RAM, including functions! Squirrel supports your own memory management by simply implementing your own malloc, free and realloc. I think with quite some effort you can build them in a way so that a malloc for a function is able to return a flash address. You will then still have to manipulate the related memcopy... I never tried that.

Ergo: For very small micros I don't see Squirrel fit. I recommend at least 512K RAM for halfway decent stuff, and 16K even for "hello world" kind of tasks!