ZX-News #36 02 июля 1997

processors - Sly processors or programs that are consistently in the same place "hang".

            Sly processors



                      - I told DI: HALT

                      - So what?


                         Alexander Mayorov

                             Dmitry Lomov


  You, dear readers, have not met
programs that are stable in one and
the same place, stuck on?


  Well, the reasons for this are many, but
another:


  Certain program on startup "hung", and
with the question "why?" on Scorpion clicked "Magic" ...


  And something happened? Here's what:

  Processor executes the command HALT when prohibited 
interrupts! 


  And the same "effect" there was still some programs.

  Of course, after the processor
"Pushed" through the HALT, program
earned ...


  Since it is unlikely that the authors of the programs "did 
not see" this "glitch" when debugging program, the question 
"what is it?" it seemed, had no answer ...



  It turns out, all due to processor
KR1858VM3. Its interrupt system is somewhat different from 
corporate Z80. 


             Item number one:

  In the case of the command HALT ban
interrupt is ignored. That is, the team
DI disables the interrupts and they are impossible
up until the processor does not stumble on
HALT. At the time of execution HALT interrupt
allowed, and as soon as an interrupt occurred, again denied.


             Item number two:

  While waiting to interrupt on command
HALT is not satisfied regeneration cycle memory. To anything 
fatal it does not lead, as the recovered memory video 
controller. In the case of a standard processor while waiting 
for HALT inside processor generates and executes commands NOP, 
and together with them through the cycles regeneration. As a 
result, the CPU VM3 register {R} does not change during the 
execution of HALT. 

 Item number three, the previous result:

  During the execution of HALT reaction
interrupt when a request is instantaneous. The standard 
response to the same CPU interrupt occurs only after the 
execution of the current single command NOP. 


      Ruleznoe consequence of paragraph three:

  When writing a multicolor inside a string (for example, the 
chessboard), a standard processor to align the entire program, 
so during her performance of HALTa HALTa to a multiple of four 
(here also need to consider confirmation of the cycle

interruption). If the program does not align
then there are "drozhalki" horizontally
as the time between the occurrence of the interrupt and its 
confirmation depends on the phase bypolneniya idle NORov 
(irregularity from zero to three cycles). In the case of the 
processor VM3 time between the occurrence of the interrupt and 
its acknowledgment is always zero (if a HALT). Therefore 
processor VM3 indispensable at the stage of debugging 
multicolor. 


  The processor is an analog 1858VM3
Z84C004 (Z80A), excluding the above
circumstances.


  That's it!


        __________________________



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