Public Spirit #01 17 мая 1997

Программирование

Coder - transfer of the screen for the interruption, Packers.

 Music: author:
(C) Dave (a) DEX '

                      (C) SEM


    In the ZX-POWER # 1 went debate
about what is possible-if
throw a screen from RAM to video
less than one interrupt.

    Let's look better
and make some calculations:
So we know that the most
the best way to transfer
data is the so-called 'Stack'
way. Its essence is to
following:

    The stack is installed on
the last byte of the field to
to bandy
information. Then, in the HL
loaded a couple of bytes to
transfer is done PUSH
HL.Takim way for 11 cycles
(PUSH HL) and burn at once
2 bytes. This is the same operation
holds for the remaining
information. Unconditional
advantage of this method
in the rate of transfer,
but the main drawback
ways are hard
requirements to
Total free memory
(Briefly, eats lots of memory).

  Now, from theory to practice:

    Method using
cycle immediately dismisses as not
fastest. It only remains
turn in all memory
filling its many
blocks of type:

LD HL, # NNNN; of thrown

               ; Bytes (1)
PUSH HL; actually

               ; Transfer


    Number of blocks
determined by the length
spreads block codes
divided by two (since
spreads on two bytes for
times).

    Now let's return
to the topic: we need to
throw a screen (6912
bytes). Hence it is necessary
raskrunchitsya at 13,827 bytes
(6912 / 2 is the number of structures
type (1) = 3,456 and multiplied by 4
(Number of bytes occupied
construction). = 13,824 and plus 3
bytes on the command LD SP, # 5B00).

    We now calculate
number of cycles occupied
the entire procedure.
(10 +11) * 3456 = 72576 cycles.
10-number of cycles LD HL, NNNN
1911 - ------//-------- PUSH HL
3456 is the number of repetitions.


   Concludes:

For branded machines are unable,
TK There we have 70,000 Bar.
But you can spill over into
MACHINES WITH MORE THAN 72,650
Bar. TK We still
REMEMBER, install and
RESTORE THE STACK AND MOST
MAIN CAUSE OF PROCEDURE AND
BACK FROM HER.

Here we thought, felt and
Now think, do we need
this transfer?

    Practical benefits from
this is no. After all, we barely
enough cycles to the deployment, and
who need to throw
static image 50 times
per second?

    But we need it yet
change, and this is the second
interrupt (if not third). For
sim to draw final conclusions:

 Throw POSSIBLE, BUT NOT NECESSARY!


    Question please consider
closed.

Thank you for your attention, DSEEMX.
I mean
SEM and DEX.
or
DEX and SEM.

(C) CODERS 'ACADEMY
4:44:35 AM 21/04/97. AD