Programming

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You can run strace on linux to see all the calls it makes to the kernel, and possibly to other libraries. On Solaris and AIX, strace is called truss, and on HPUX, tusc (available open source). The Solaris version can capture all lib calls using option: -u'*'

You can get the code reverse assembler analyzed, but it might not be very friendly unless you are an x86/64 assembly guru.

I work in C/C++/JAVA a lot, where every byte is pretty well under my thumb. Other compilers and languages sometimes do you unwelcome favors. Even in JAVA, System.out.flush() doesn't. PERL is nice, too, sort of a script/C/C++ cross, but not my forte. Others give me pause!

Weird that some printouts there seem like printf format strings! Maybe the 'fixed checksums' are punctuation words, like with mime multipart separator strings.

They might just have a final checksum that checks it all. Be careful. The answer is always somewhere inside or outside the box, so when you get stuck, stop trusting your assumptions and competence! Good placement of monitoring is critical, as you can see! Are the NULs real characters or the line marking? Something like '[CAN]r' might be a short integer, maybe unsigned. I assume NU is a mangled NUL.

I tried analysing a microcontroller assembler level program before, i've done it because i already programmed the same target in assembler before, so i understand what you mean that it could be not friendly if you are not familiar with the language, i will give a try with strace if i found clear calls to chks calculating libraries maybe i continue, else i will have to emulate the communication.

no, it still a direct calc of number of bytes :
The Nuls are end of line markers in the habitual meaning or in strings handling but here its not, its just a 0x00 byte and the binary file is full of em, same in the start of a line. and the NU is a mangled NUL.
But for the "CAN r NUL EOT", this is the 4 bytes repetitive command part of the headers, i dont think if it have different type from other 8bits data as its transfered by the link, so if it is in different type then it should have special treatement of testing the first 8 bits and then concat second ones if for exemple its in 16bits format. those are not outputs, but communication frames.
But the whole line must have a meaning, maybe as you noticed about the languages equivalent in low level.

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Oh didnt noticed this rule Corona, i will pay attention next time. thx

strace does not show function calls, it shows system calls. It can tell you exactly how the port is being configured and what data is read and written in what order when.