Programmers - assembler: Excursion to the anatomy of the ZX

<b>Programmers</b> - assembler: Excursion to the anatomy of the ZX

     Digression into the anatomy of the ZX

(C) DICTATOR
_______________________________


            Prologue.


            "And here to submit this

               Tyapkina-Lyapkin!


   The reaction of readers to the cycle
"Assembler for Dummies" has been
so extensive and unexpected that plunged us into deep
reflection of the impermanence of all things. By and large, all 
responses can be divided into two types: "This is that - evil 
joke?" and "We do not kitchen utensils, our food

for the brain is needed, but not for ...".
In a word all consider themselves
at least "start" and require that it requires deeper
their knowledge.

   Well, here we are, what you
answer. Unfortunately, not enough just to know assembler,
to teach him to others, we must also
and be able to teach. And, as shown
practice, these two qualities are somehow trying to avoid each
other. At this stage we are still
failed to find a person suitably qualified in
both of the above manifestations, but
hope, as we know, dies
the latter, and perhaps you have
can read in our magazine
a full course of "A" to "RESET
INTERRUPTION ".

   In the meantime, are continuing the search, we decided to 
publish some feature articles covering the most frequently 
occurring in "initiating and enhance" the problem. In the next 
issues we ZF going to address the following

directions:

  - Optimization of programs for speed and time;

  - Faster graphics;

  - Wretchedness of the TR-DOS, and how this
fight;

  - 3D-vector and 3Danimatsiya.


   Changes to this list
possible, even necessary, and will be produced, mainly
based on your letters. Sitting at home in myagom chair with a 
bottle of beer, the author can not guess what do people want - 
bread? spectacles? 3D-joystick? or too

beer? Wherefore write, call,
come and express their thoughts
about the need for one or
a theme (it is better to write).


         CHAPTER ONE.


               "Tell me, what

           program you wrote,

             and I'll tell you who you are. "


   Duty is the author repeatedly faced with the following 
situation: there is a newfound genius, and looking at the world 
down, it presents itself to the world the creation, which is 
comparable to his genius author. But at the first testing are 
clarified some details: shaking the cursor at the top of the 
screen, twitching sprites program speed is not uniform ... And 
all this only If a new masterpiece in general

deign to work not only on
machine of its creator, but also at
would be at half mass-produced computers.

   Global causes of this unfortunate case is usually two:
 a) present the programmer does not adhere to any standards and 
regulations, or the only correct said his car;

 b) this individual is related to
category of very good teachers.

   But, as with the second paragraph
This summary is almost impossible to fight, we will focus on
first, namely talk about
standards.


   Each sinkleristu from the cradle
should be aware that such
masked interrupt and what they need. If for kakimlibo reason 
you missed this significant period of life or

Your childhood was held on the keyboard IBM PC, then maybe you
is not without interest to learn some details about this 
insidious phenomenon. 

   Masked interrupt signal (hereinafter INT) is generated
Simultaneity with the arrival of personnel
clock having frequency
50 hertz (50 times per second). By
the arrival of the same human clock starts construction of the 
video, but considering the hardware features of both your 
computer and the monitor screen, construct a larger size than

actually observed. In the standard computer build time
eight horizontal pixels
takes 4 stroke engine, one
a horizontal line - 224 cycles, while the number of lines on 
screen - 312. Thus we can calculate the number of clock cycles 
that the processor can execute during construction of the 
entire screen - this number is about 70.000 cycles. It is also 
worth noting that this includes the time quenching INT, but it 
is not as significant a factor, in addition to his 
understanding of the need to understand in computer 
architecture and not on amateur level.


   The prose of life is
that this is a purely theoretical
meaning and practice to
bear in mind that the RAM usually works brake ROM and it makes 
adjustments in performance. 

  Observant reader will have
guessed that the video controller ZX
displays the screen much faster than it can build
program, because the elementary team LDI takes 16 clock cycles, 
and construction of eight bits of the screen - 4

tact. So, if you start to rebuild the screen simultaneously 
with the arrival of INT'a and trying to capture the entire 
screen, in the middle of this noble classes videocontroller you 
catch and surpass, and the rest

screen will be shown only in
the next cycle interruption. As far as the author of this 
manuscript, a large part of the new generation of programmers 
all of the above have not yet realized, and continues to rivet 
the trembling and blinking cursor sprites. How to combat these 
phenomena and dedicated to the next chapter.




         CHAPTER AVERAGE.



              "Nothing works


                     for so long. "



   To learn why there trembling cursors
consider the whole process in detail. Standard algorithm cursor 
system is usually as follows: 

 1. remember the buffer contents of the screen to the point 
where the cursor will be displayed;  2. superimpose on the 
screen cursor by mask;

 3. Examine the keypad, recalculate the coordinates of the 
cursor;  4. restore contents

screen at the cursor in the previous position and go to
Item 1.


   Naturally begs the question
timing of all this business with
preemption and, consequently,
beginning construction of the screen.

   The optimal output
is to use the command
HALT between the third and fourth
paragraph and the minimum number of
procedures, hanging on the interrupt
or better yet a complete lack of them
or priority allocation
at execution time. And then the fun begins.


   From the beginning of the video screen before the first 
pixel number of working screen (ie the beginning of a video 
buffer, located on the addresses # 4000)

in a standard machine is built 70 lines curb, which takes 
15,680 clock cycles. However, an abundance of mysterious 
(read-brake) circuit decisions on some computers causes the 
stick to a few other figures. The author had never seen 
vehicles braking Scorpio and therefore recommends that you stick

critical reading of this machine, namely the 60 lines, which is 
13.440 cycles. 

   So, if the procedures are erasing the cursor, copy the 
buffer and overlay the cursor fit in beyond that figure, the 
cursor looks very nice and not even has no chance to arrange

megadrozhanie in any part of
Spectrum screen. Bright
example might be a shell
ZF and, in particular, MEMORY TEST
of the second issue of shadow businesses. If
You look carefully, you
notice that the two cursors simultaneously processed, the 
aggregate amount of which is 10 familiarity.


   Preliminary results
all of the above, the author apologizes if you
something was unclear because of the inability of the author 
himself available to present the material in paper. But if 
you're still reading and you are still wondering I probably 
will state summary the first part.


   The main requirement for the program, working with the 
dynamic graphics is: no matter what side of the screen, this

programa or rebuilt, at
Whatever it is machine or work,
for the absence of flickering images during the construction 
thereof, video controller does not have to cross the tunable 
range. In this case, no importance,

You overtake him, or he you.

   Despite the fact that in this
chapter has outlined the basics
anatomy of the ZX, it should be
at least enough to
early experiments, which
sooner or later will lead you to
full consensus with dynamic graphics and border lines.

   But, as history has shown clearly, the experiment experiment 
strife, and severity of the knife need to check on someone 
else's throat. Developing this idea, we quietly

crept up to the next chapter of
which you may podcherpnete something interesting about the 
methods debug programs that are critical for

time and location in the loop
interrupts.



     CHAPTER almost the last.



                "I figeyu, Toshiko,


                 bamboo bloomed. "



   Many programmers often
concerned about the issue "but as a long running my new / old / 
better / in-depth treatment?". If you have not guessed it done 
any hardware gadgets, and your brains are not predisposed

to distort the course of thought, then,
most cases, the silence will be your answer. However, as
said the classic, all brilliant
simple method described below and fully consistent with this 
thesis. 

   The first thing you should turn off all the turbo mode and 
the brakes and bring the car in the most close to the standard 
mode work. Next take a strip of

paper 2 cm wide, 97 mm tall with a display of your favorite
TV or monitor and nail it to this very screen.
After finishing this lesson vysokointelektualnoe, download TASM 
4.0 (XL Design) and tamp the following

program:


       ORG # 8000

       DI; creation

       LD HL, # FE00; vector

       LD A, H; masks
       LD I, A; emyh

       INC A; interrupt
       LD (HL), A; vany

       INC L

       JR NZ, $ -2

       LD C, H

       INC H

       LD (HL), A

       LD L, A

       LD (HL), # C9

       IM 2
; The main loop, in other words
; The very essence of
LOOP EI

       LD B, 7

       HALT

       OUT (C), B
OOPS DS 13440 / 4,0

       OUT (C), 0

       XOR A

       IN A, (C)

       CPL

       AND # 1F

       JP Z, LOOP

       LD A, # 3F

       LD I, A

       IM 1

       EI

       RET


   It should be noted that the reference TASM 4.0 (XLD) was not 
accidental. This product is recommended due to the 
implementation of it the commands such as OUT

(C), 0, and DS.


   The result of this
program will strip white
color on the black borders, synchronized with the start screen.
Next, you should take the felt-tip pen and glued to hold on
TV piece of paper a line parallel to the bottom of the white 
stripe. Next to this feature please "13.440" and if you have 
not yet understood the essence of the method, then the medicine 
is here powerless (good joke). The attentive reader will have 
guessed sense of lines of code that is marked Tagged OOPS. It 
creates in memory of 13,440 / 4 = 3360 teams

NOP, and the implementation of which is actually 13,440 cycles.
Thus, after sitting ten
minutes around the monitor with a felt pen in his mouth, 
substituting it line values in thousands of cycles, you will 
form a scale which will enjoy the rest of adult life. If you 
prefer, you can make marks on the every thousand cycles, but 
this Of course, if you have the patience and

ink.

   We now turn to the second
Part of this method. To determine where in the cycle
interrupt routine is defined, and what time
it runs, you need to do three basic things:

 1. before the desired sub-program to put a conclusion on
border of any color different from the primary color
border;
 2. at the end of the subroutine to restore the background color
border;
 3. look at the curb in
run time, where
is a dedicated semiconductor and,
accordance with the scale to calculate its duration.


   In most cases, particularly if you have a little fancy 
programming real-time reaction of the experimenter in other 
words, full ofigevanie and appeal to the

Toshiko great, not name.
If now you do not understand the essence
this method, then direct you to the road to the club Dendy 
MegaYunior or to the nearest store for PENTIUM-133.


   That's how, step by step, we come to the final part of 
today's lecture, which summarizes the basic requirements for 
the programs and programmers, as well are some useful health 
tips. 


                            ...