z80
[Continued (in readers' letters)]
(C) WLODEK BLACK
MONOZAGRUZCHIK
... Hello again, friends. I hope you have not erased files
great demos of all time named
"DIGITAL TUNE 1"? We return to our ... Hmmm ... Okay, we
just come back. In the past (or rather, one might say, the year
before ...) once we got to the point where before our eyes
appeared 4 files are the compressed data - one for each of the
pages 19, 20, 22 and 16. I packed LZPAC-ohm, and I turned the
following figures: dt1.19 <- 4472 bytes, 18 sectors;
dt1.20 <- 4812 bytes, 19 sectors;
dt1.22 <- 4494 bytes, 18 sectors;
dt1.16 <- 6410 bytes, 26 sectors.
I used the names for files built on the principle: "dt1" -
the words "digital tune 1" "19" (also "20", "22", "16") - number
page RAM "<" - means that the file is packed (ie, became
less "). Of course, you can use any other names.
Anyway in the end everything will turn into a single
file.
Now let's merge these 4 files into one. Download the "dt1.16 <"
address 28964, and subsequent files ship close to each
groomsman, ie "dt1.20 <" ship to address is 28964 4472, and so
on. Then unload the big file:
SAVE "dt1. <" CODE 28964,20188.
Check the following: 28964 20188 = 49152, ie, the boundary
started switching pages of RAM. In this case, the memory is the
place to take immediately the entire volume of packed codes.
Then start the program "raspihaet" individual pieces of code
block on page 19, 20 and 22. By the way, we still have packed a
picture!
A set of standard functions TR DOS.
For programmers writing in assembler, TR DOS provides
fairly extensive set of so-called standard functions that
perform these necessary actions, such as working with files and
separate tracks and sectors - search, read, write - and more. A
complete list of features can be found in any instruction to
the computer, which provides guidance on the use of TR DOS, so
here I will not repeat. I can only say that to refer to the
standard functions TR DOS to Record number calls a subroutine
in register C and perform CALL # 3D13, a pre zanesya input
parameters in other registers. For us now it is of interest
feature number 5 - reading group sectors. Input parameters for
it are starting track and sector and the number of read
sectors, as well as the address to which you begin to download
data: DE - initial track / sector (E - Sector, D - Track);
B - number of read sectors;
HL - address of the boot.
File structure of disk TR DOS is very simple. Files are stored
on disk in the order they appear in the directory. Each
subsequent file starts with the track / sector, going beyond
the last sector of the file. System variable TR DOS, located at
# 5CF4 (two-byte word), keeps track number and sector,
following after the last read sector. Upon completion of
download of any file in this cell will be like a pointer to the
beginning of the next file. Based on the above, it is easy to
assume that you'd like to download the following file (or any
part thereof) - we must take meaning of a word from a cell #
5CF4 and put it in a couple of DE as the "track / sector" for
the function 5: LD HL, adres_zagruzki
LD DE, (# 5CF4)
LD BC, # XX05; where XX - number of loaded sectors
CALL # 3D13.
To use such admission must comply with the simplest condition -
the files to the boot sequence should be recorded one after
another without having erased files between them. And now -
please! With the file type "BASIC program" TR DOS operates with
one interesting feature: when downloading Beysikprogrammy for
execution TR DOS takes from the disk directory file length in b
and d t and x, not paying attention to the length in sectors.
It calculates the number of sectors corresponding to the
specified directory in length, in bytes, and the ship just
enough. If Beysikovy loader has a length of, say, 209 bytes and
the length of the sectors listed, for example, 68 - on command
"RUN" or "LOAD" will be loaded only one sector corresponding to
the size file of 209 bytes. That this implies a great
opportunity to join together into one file and Beysikovy
loader, followed by a block of code. You can do this, of
course, vruchnuyuslozhit length boot sectors and the subsequent
file (s) Record the result in the file length in sectors BASIC
loader, and carefully remove from the catalog of obsolete
pointers (handles) on the data files. And then adjust data in
the 9-m sector, so that the number of files has been turned out
and match the options "the first free track / sector", "number
of free sectors" carried in themselves the true values. This
can be done by any "disk doctor". Work, of course, not too
complicated, but if you make a mistake, the very first new
recording on the disc will fail! Fortunately, there are tools
with which to "merge" the files at the touch of a button, and
without any risk. One of the most famous of these is the
Advanced Disk Monitor - ADM 7.08. To merge files in the ADM
point to the initial file, and then Symbol Shift + C (connect -
connect). In your eyes lower part of the directory "tighten" to
the original file, subsequent to the the initial file will
disappear, and the initial file popolneet the value volume of
"missing" file. Operation can be repeated for podlivaniya more
than one file, etc. Consolidate the changes made by using the
rename operation: press N; if necessary, rename the file, press
Enter. The result is written to a directory on disk. In
conclusion, cite the full text of the loader and start the
program for the demos "DIGITAL TUNE 1" with comments:
DI
LD HL, 50000; load address packed pictures
LD DE, (# 5CF4); track / sector
LD BC, # 0F05; 1915 (# 0F) sectors to read
XOR A
CALL # 3D13; call TR DOS
CALL 50000; unboxing pictures on the screen
DI
LD HL, 28964; load address of the main unit
LD DE, (# 5CF4); track / sector
LD BC, # 4F05; 1979 (# 4F) of sectors to read
XOR A
CALL # 3D13
DI
LD A, 19, page number
LD HL, 35374; start address data for page 3
LD DE, 4472, the block length codes
CALL LDIRDT; sends to the third page
LD A, 20, also for 4-th page
LD DE, 4812
CALL LDIRDT
LD A, 22, also for 6-th page
LD DE, 4494
CALL LDIRDT
LD HL, 35373; move
LD DE, 37641, in its place
LD BC, 6410; block codes
LDDR; main memory
CALL 31232; extract the main unit
LD A, 23; includes 7-th page (as necessary)
LD BC, 32765
OUT (C), A
EI
CALL 31238; initialize music
LOOP: CALL 31232; losing DeMouy
JR LOOP
LDIRDT: LD BC, 32765; routine raspihivaniya from memory
PUSH BC
OUT (C), A; includes a page
LD C, E; transfer from DE to BC, how many bytes ...
LD B, D
LD DE, # C000; ... should be forwarded to the address #
C000 ... LDIR; ... and forwards
PUSH HL
CALL # C000; extract
POP HL; restore HL and BC
POP BC
LD A, 16, restoring the main memory
OUT (C), A
RET; return.
That's it. Bye!
[Continuing the theme of "assembler" should be].
