ZX Pilot #29 30 сентября 1998

Софт

HARD and SOFT - Error STS v6.2 and fixing it.

 HARD AND SOFT


(C) IVAN ROSCHIN


       Error in STS 6.2 and fixing it.


   When referring to drive STS 6.2 (as well as older versions)
believes that in case the actual recorded tracks VG93
The track number on which the magnetic head drive.
But for various reasons in case the track may contain invalid
value, and in this case, any operation with a disk will be 
completed with an error.


   Suppose we loaded the STS with the drive 'A', and after
load magnetic head is located, for example, the 10-th path
(And the contents of register paths, respectively, equal to 10).
Establish Drive = 'B'. What if this happens? STS will not be
initialize the drive to install the magnetic
Head to the initial state (at zero track). STS will not be
perform and read the first team got the title
sector to find out what path is the magnetic
head (like the TR-DOS). STS believes that and
drive 'B' magnetic head is on the 10 th track, and
move it to 10 steps backward for positioning on the 0-th
track (to read the directory). If the magnetic head
really is on the 10 th track or on track with
smaller rooms, all completed successfully. But otherwise
If, you know - after a long wait Color
border changes to red, signaling a disk error.
Moreover, we can not go back to the drive 'A' - STS
believes that he has already established a magnetic head on the 
0-th track, and she remained at the 10 th ...


   Such troubles arise not only when working with two
drives, but, for example, when debugging your own programs
to the disk, which alter the contents of the register
track. Assembliruem such a program, run - and then
STS refuses to work with the disk. And the old version of STS 
in general stuck in disk errors ...


   Fortunately, there is a simple way to overcome this problem:
enough to go to the TR-DOS, see the directory of the drive and 
return in the STS. In this case, the contents of the register 
comes into the track conformity with the reality that the 
magnetic head drive. 

   And if you go to the TR-DOS does not want (or not)? In this
case will have to make some changes in the STS. How did this
do?

   You can determine where the STS routine is called reading
directory (it is called, and when you change the drive), and 
before each its challenge to implement code that initializes

drive - and the problem is solved! But after some thought, I 
found more simple way: instead of initializing the drive should 
write to register tracks some sufficiently large number (at

At least more than 160), for example, 255. In this case the STS 
at positioning of the 0-th track moves the magnetic head on

255 steps backward, and wherever she was, she must be
the 0-th track (as required).

   Thus, changes made to the STS: routine reading a directory
is located at # E7F8, and called it the following command:
# E495: JP # E7F8. At # E495 put a team on the transition
piece of software that writes the register 255 in track. That 
this fragment:


LDA, 255; this number track record in the register
LDDE, # 1E3A; in ROM TR-DOS: # 1E3A - OUT (# 3F), A: RET
CALL # E4D3; appeal to the TR-DOS ROM
JR # E7F8; proceed to read the directory


   Where can you find for him a free place? At # E7CF
find a program section, reset the attributes of the screen. STS
sometimes uses for its own needs lower third of the screen
(# D000-# D7FF), and that it was invisible, for it establishes a
Null attributes.

 # E7CF: EXX
LDHL, # D800
LDDE, # D801
LDBC, # 02FF
LD (HL), L
LDIR
EXX


   Here and place our fragment:

 # E7CF: JR # E7DD; to bypass the fragment
 # E7D1: LDA, 255
LDDE, # 1E3A
CALL # E4D3
JR # E7F8


   At # E495, respectively, put the team JP # E7D1. Well
that, one can only write the modified STS on disk - and
You can work with.


° ° ° ° °