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<div class="moz-cite-prefix">On 2021-01-31 2:57 p.m., Mark H wrote:<br>
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<div dir="ltr">Hey guys,
<div><br>
</div>
<div>I have a small project with Jim on an STM32F4
microcontroller. It has about 104 KB RAM available to the
app. That actually works pretty well, and can navigate its UI
on a 20x4 character LCD. I expect to use Jim on other MCU
projects as well.</div>
<div><br>
</div>
<div>Predictably, it's starting to have serious RAM-cram. So
I've been looking at ways to run scripts directly from where
they reside in flash (effectively ROM). That way the entire
application script (plus Jim stdlib) doesn't get copied to RAM
before it even begins interpreting. And then each proc body
copied to more RAM etc. </div>
<div><br>
</div>
<div>So, some open questions:</div>
<div><br>
</div>
<div>1) Has anybody else tried something similar? How did you
approach it and how well did it work?</div>
<div><br>
</div>
<div>2) I've tried a few approaches so far. Each of those has
"almost" run correctly. The basic problem is that Jim's
(0.79) hashtables and certain other functions rely on
null-terminated strings. They discard or ignore the (in most
cases) known length of the string. But those nulls are not
present when (for example) command or variable name tokens
point to ROM instead of RAM, because I've shut off the strdup
that would have made the RAM copy. The original script in ROM
has the remainder of the script where the interp is expecting
the null to be. I've tracked down and fixed those issues in a
few important functions, but certainly not all. I've gotten a
few lines of script to run that way, so it probably can work
for the rest. It looks like it might be a long road to
complete that approach, and would likely introduce bugs
wherever i've missed a spot. I have no obvious way to run
Jim's test suite on such a small host, and no obvious way to
make scripts read-only on a PC to run the tests there
instead. So...</div>
<div><br>
</div>
<div>3) ...Instead, I'm starting to seriously consider a
comprehensive solution. Such as: throughout jim.c, replace
all char* function parameters with a new structure instead,
such as "Jim_Text", which carries both the char* and the known
length. That would mean basically a wholesale paradigm shift
from C-style strings to known-length strings. You might say
Pascal-style strings, but I wouldn't store the length at the
front of the string data like Pascal does. That makes it too
easy to overlook a piece of code that needed the rework,
introducing insidious bugs. The new design should pass all
existing test suites verbatim. And it should be able to do so
on a PC, where the tests are available, proving that it's
likely to also work on the MCU, where tests aren't available.</div>
<div><br>
</div>
<div>4) Is anybody else interested in seeing that approach
adopted? There might be other benefits besides running
scripts from ROM. One benefit might be a bit faster
execution, since most strlen() calls or other null-byte
searches are eliminated. Currently those are happening every
time a hash key is computed, and in other hotspots.</div>
<div><br>
</div>
<div>5) I heard Steve mentioning recent improvements to make
Jim insensitive to nulls embedded in data. Anybody care to
guess how that work interplays with this approach?</div>
<div><br>
</div>
<div>6) Would anybody else be interested in helping with the
extensive rework?</div>
<div><br>
</div>
<div>7) Are there any Tcl TIP's, or Jim open issues, that
relate to my goal, or to this paradigm shift either?</div>
<div><br>
</div>
<div>Thanks for any clues!</div>
<div><br>
</div>
<div>--</div>
<div>TheMarkitecht</div>
<div>
<div dir="ltr"><span style="font-size:12.8px">"I'm always
disappointed when a liar's pants don't actually catch on
fire."</span><br>
</div>
<div dir="ltr"><a href="https://github.com/TheMarkitecht/slim"
moz-do-not-send="true">https://github.com/TheMarkitecht/slim</a><span
style="font-size:12.8px"><br>
</span></div>
<div dir="ltr"><br>
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<p>Hi Mark</p>
<p>I am sure that Steve knows best with this but just for the
record, I have wanted to do something like this too. What OS are
you running? Even if the microcontroller has memory, is there
anything to stop us from using external memory? Perhaps over SPI
etc ..</p>
<p>BTW, if you do go down the Lua road, I was part of eLua and I can
tell you what I learned from this, just PM me.<br>
</p>
<p>-Pat<br>
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