• More of my philosophy about Intel 8051 controller and about preemptive

    From Amine Moulay Ramdane@21:1/5 to All on Sun Nov 28 14:14:30 2021
    Hello,



    More of my philosophy about Intel 8051 controller and about preemptive and non-preemptive timesharing and more..

    I am a white arab from Morocco, and i think i am smart since i have also invented many scalable algorithms and algorithms..

    I have just quickly read the following interesting paper and it says
    that judicious use of cooperative tasking techniques can also often meet an embedded system's multitasking requirements, while giving better
    performance and a simpler software environment than a preemptive multitasker, so read it carefully here:

    https://users.ece.cmu.edu/~koopman/pubs/koopman90_HeavyweightTasking.pdf

    And notice that it also says in the above paper that so that to meet
    the requirements with cooperative multitasking you have to move the time-critical code to interrupt-service routines. And let us look
    for example at the Intel 8051 controller here:

    https://www.electronicwings.com/8051/introduction-to-8051-controller

    So as you notice that it has many hardware interrupts that you can
    use so that to make the cooperative tasking efficient, and i think it also comes with two clock timers interrupts that you can use to implement preemptive multitasking if you want, and you have also to know about interrupt latency when programming
    embedded systems with hardware controllers, and you have to know that the hardware interrupts have to get serviced fast enough and often enough, so you shouldn't disable
    interrupts for too long a period of time, and just to give you an idea
    , look for example at the nonbuffered communication UART (Universal Asynchronous Receiver Transmitter) operating at 38,400 bits per second will interrupt every 208 microseconds. This is 1/38,400*8 because they
    will interrupt for every byte (8 bits), and a processor or controller running at 25MHz executes most of its instructions in
    2 or 3 system-clock periods. That would be an average of 120 nanoseconds (1/25,000,000*3). In theory, this means you could execute as
    many as 1,730 instructions in the interrupt interval. So that was only
    in theory, now you have to do the reality check. You must take into consideration that there are more interrupts than just that communication channel. The timer interrupt will be firing off every so often. And the communication interrupt itself will have interrupts
    disabled for good period of time, and not only that, but there is also the tasks switch that can be expensive, so you have to think about
    it efficiently.

    So i invite you to read my below thoughts preemptive and non-preemptive timesharing and more so that to understand much more efficiently:

    More of my philosophy about preemptive and non-preemptive timesharing and more..

    I have just took a smart look at Modula-2 language(Modula-2 is a structured, procedural programming language developed between 1977 and 1985 by Niklaus Wirth at ETH Zurich, and he has also developed Pascal
    language, read about Niklaus Wirth here: https://en.wikipedia.org/wiki/Niklaus_Wirth), and i think Modula-2 language was among the first languages that has provided preemptive and non-preemptive timesharing with coroutines, but the preemptive timesharing
    in Modula-2 uses Interrupt handling using IOTRANSFER, but it is best reserved for programs that will run without operating system support. Installing an interrupt handler on a multiuser system is not feasiĀ­ble because doing so would affect other users. (
    For this reason, IOTRANSFER is not a mandatory feature of Modula-2.) Even on single-user systems, IOTRANSFER can be difficult to use because installing an interrupt handler causes the old interrupt handler (which most likely belongs to the operating
    system) to be lost. So this is why i think that the best way in modern operating systems is to use non-preemptive timesharing with coroutines, so this is why i am providing you with my sophisticated implementation of stackful coroutines, read about it in
    my thoughts below:

    More of my philosophy about timesharing that is a Solution to Computer Bottlenecks..

    I invite you to look at the following very interesting video about timesharing that is a Solution to Computer Bottlenecks:

    https://www.youtube.com/watch?v=Q07PhW5sCEk

    I think i am smart, and you have to understand one important thing
    and it is: What is the difference between a software architect and
    a software engineer?, i think there is an important difference and it
    is also like abstracted in the following question:

    "How it is made?"

    So i think that software engineering works at a higher level than
    a software architect, this is why you will notice that i am
    quickly implementing a sophisticated stackful coroutines
    Library and i am quickly implementing setjmp() and longjmp() with
    x64 assembler or code machine, read my below thoughts about them, but you have to know that my sophisticated stackful coroutines Library
    does a kind of timesharing as in the above video, but i think that there is two kinds of timesharing: the preemptive one, and the non-preemptive one, but the difference is that the preemptive one does interrupt with a timer the coroutines from an
    external scheduler in
    a form of function, but notice below that i am implementing the non-preemptive timesharing in my sophisticated coroutines Library, but you have to be smart and notice that my way of doing is like the software architect way, since i am implementing it
    from the lowest level with x64 assembler routines that are part of the non-preemptive scheduler, but not only that, but you have also to look at how i am also implementing a
    sophisticated and much more rich interface in my stackful coroutines Library, so it is like both software achitecting and software engineering, so here is all my below thoughts that shows how i am implementing it quickly, so read it carefully since you
    have also to know what's the problem with the stack frames when architecturing and using the setjmp() and longjmp() so that to implement coroutines:

    More of my philosophy and precision about the link of the article and more..

    And notice that the link below of the article that shows the problem
    of implementing coroutines with just setjmp() and longjmp()
    is from the last semester of the second year of the course
    called "CS4411 Operating Systems" from Michigan Technological University, but i think i am smart and those courses are easy
    for me, so i invite you to read about this course that requires
    both the course of "CS3331 Concurrent Computing" and "CS3421 Computer Organization", and here it is:

    http://www.csl.mtu.edu/cs4411.ck/www/Home.html

    More of my philosophy about coroutines and about setjmp() and longjmp()..

    I think i am smart, and i will say that with setjmp() and longjmp()
    you can implement a generator or the like, but you can not implement coroutines with just setjmp() and longjmp(), and so that to understand it, i invite you to read the following article that shows how when you yield from a first function with a longjmp()
    to the main body of a program and when you call another functions with longjmp(), it can make the stack frames not work correctly, and when you understand it you will not use setjmp() and longjmp() alone so that to implement coroutines, so read the
    following article so that to understand the problem with
    the stack frames, and i am understanding it easily:

    https://www.csl.mtu.edu/cs4411.ck/www/NOTES/non-local-goto/coroutine.html

    So this is why i have also implemented my sophisticated stackful coroutines library so that to solve this problem, and here is my sophisticated coroutines library and read about it and download it from here:

    https://sites.google.com/site/scalable68/object-oriented-stackful-coroutines-library-for-delphi-and-freepascal

    More of my philosophy about setjmp() and longjmp() and generators and coroutines..

    I have just quickly implemented setjmp() and longjmp() in x64 assembler,
    and after that i have just implemented quickly a good example of a generator with my setjmp() and longjmp(), look at it below, and in computer science, a generator is a routine that can be used to control the iteration behaviour of a loop. All generators
    are also iterators. A generator is very similar to a function that returns an array, in that a generator has parameters, can be called, and generates a sequence of values. However, instead of building an array containing all the values and returning them
    all at once, a generator yields the values one at a time, which requires less memory and allows the caller to get started processing the first few values immediately. In short, a generator looks like a function but behaves like an iterator. So here is my
    implementations in freepascal and delphi and they are working perfectly:

    Here is my first unit that implements longjmp() and setjmp() and notice
    how i am saving the non-volatile registers and how i am coding it in
    x64 assembler:

    ======


    { Volatile registers: The calling program assumes registers
    RAX, RCX, RDX, and R8 through R11 are volatile.
    The contents of registers RBX, RSI, RDI, RBP, RSP, and
    R12 through R15 are considered non-volatile. Functions return
    values in RAX. }



    unit JmpLib64;

    {$IFDEF FPC}
    {$ASMMODE intel}
    {$ENDIF}
    interface

    type
    jmp_buf = record
    RBX,
    RSI,
    RDI,
    RSP,
    RBP,
    RIP,
    R12,
    R13,
    R14,
    R15: UInt64;
    end;

    { setjmp captures the complete task state which can later be used to perform a non-local goto using longjmp. setjmp returns 0 when it is initially called, and a non-zero value when it is returning from a call to longjmp. setjmp must be called before
    longjmp. }

    function setjmp(out jmpb: jmp_buf): UInt64;

    { longjmp restores the task state captured by setjmp (and passed in jmpb). It then returns in such a way that setjmp appears to have returned with the value retval. setjmp must be called before longjmp. }

    procedure longjmp(const jmpb: jmp_buf; retval: UInt64);
    implementation

    function setjmp(out jmpb: jmp_buf): UInt64; assembler;{$IFDEF FPC} nostackframe; {$ENDIF}register;
    asm
    { -> RCX jmpb }
    { <- RAX Result }
    MOV RDX, [RSP] // Fetch return address (RIP)
    // Save task state
    MOV [RCX+jmp_buf.&RBX], RBX
    MOV [RCX+jmp_buf.&RSI], RSI
    MOV [RCX+jmp_buf.&RDI], RDI
    MOV [RCX+jmp_buf.&RSP], RSP
    MOV [RCX+jmp_buf.&RBP], RBP
    MOV [RCX+jmp_buf.&RIP], RDX
    MOV [RCX+jmp_buf.&R12], R12
    MOV [RCX+jmp_buf.&R13], R13
    MOV [RCX+jmp_buf.&R14], R14
    MOV [RCX+jmp_buf.&R15], R15


    SUB RAX, RAX
    @@1:
    end;

    procedure longjmp(const jmpb: jmp_buf; retval: UInt64);assembler;{$IFDEF FPC} nostackframe; {$ENDIF}register;
    asm
    { -> RCX jmpb }
    { RDX retval }
    { <- RAX Result }
    XCHG RDX, RCX
    MOV RAX,RCX
    MOV RCX, [RDX+jmp_buf.&RIP]
    // Restore task state
    MOV RBX, [RDX+jmp_buf.&RBX]
    MOV RSI, [RDX+jmp_buf.&RSI]
    MOV RDI, [RDX+jmp_buf.&RDI]
    MOV RSP, [RDX+jmp_buf.&RSP]
    MOV RBP, [RDX+jmp_buf.&RBP]
    MOV R12, [RDX+jmp_buf.&R12]
    MOV R13, [RDX+jmp_buf.&R13]
    MOV R14, [RDX+jmp_buf.&R14]
    MOV R15, [RDX+jmp_buf.&R15]
    MOV [RSP], RCX // Restore return address (RIP)

    TEST RAX, RAX // Ensure retval is <> 0
    JNZ @@1
    MOV RAX, 1
    @@1:
    end;

    end.

    ================

    And here is my example of a generator with my longjmp() and setjmp():


    { In computer science, a generator is a routine that can be used to control the iteration behaviour of a loop. All generators are also iterators. A generator is very similar to a function that returns an array, in that a generator has parameters, can be
    called, and generates a sequence of values. However, instead of building an array containing all the values and returning them all at once, a generator yields the values one at a time, which requires less memory and allows the caller to get started
    processing the first few values immediately. In short, a generator looks like a function but behaves like an iterator. }

    program test_generator;

    {$APPTYPE CONSOLE}

    uses
    JmpLib64;

    type PtrInt = ^Integer;

    var
    childtask,maintask: jmp_buf;
    myarr1: array of integer;
    i,a:integer;
    Ptr1:PtrInt;

    function generator(var myarr:array of integer):integer;

    var i1:integer;
    val:integer;
    ptr:PtrInt;
    begin


    i1:=0;

    val:= setjmp(childtask);

    i1:=val-1;

    if val=0 then
    begin
    new(ptr);
    ptr^:=myarr1[i1];
    longjmp(maintask,uint64(ptr));
    end;

    if val=10
    then
    begin
    writeln('Exiting child..');
    exit;
    end;

    inc(i1);
    new(ptr);
    ptr^:=myarr1[i1];
    longjmp(maintask,uint64(ptr));
    end;

    begin

    setlength(myarr1,10);

    for i:=0 to 9
    do myarr1[i]:=i;

    uint64(ptr1):=setjmp(maintask);

    if ptr1=nil then generator(myarr1);

    a:=ptr1^;
    dispose(ptr1);

    if (a<=length(myarr1))
    then
    begin
    if a=length(myarr1)
    then longjmp(childtask,a+1)
    else
    begin
    writeln('Value returned by generator is: ',a);
    longjmp(childtask,a+1);
    end;
    end;

    setlength(myarr1,0);

    end.

    ====


    Thank you,
    Amine Moulay Ramdane.

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