D M A U S C
(C) HARD
Page DMA UltraSound Card.
Introduction.
I then asked to write something
in the ZX-Pilot of DMA USC. But since about it a lot
written in other publications (RUsH # 2, ECHO
# 6, ZX-POWER # 4 will be), in particular in
Fido may be something to find, I thought (and
I have many in this regard supported) to create a small
razdelchik entitled "DMA USC - Questions and answers. "So let's
send all the pressing issues on this topic, and we (Alex and I)
try to help with the answers. All questions can be sent to the
newspaper (if you live in Within Kovrov), or the address listed
at the end of this article. Remember, the life of the article
(and SPECCY too) is completely depends on your activity!
Because not yet at that meet, then to
to kill time and disk space I give the technical
characteristics of DMA USC, and as response to criticism from
ZX-Guide # 2 in DMA USC, criticized the DMA SB.
Technical characteristics of DMA USC.
Interestingly, there are still people that do not
read it?
Number of channels: 4;
Discharge channels: 8 bit;
Adjust the volume level:
0-63 (6 bit);
Sampling rate (Rate):
48 kHz (up to 3.5 MHz);
The length of the samples: 64 KB;
Max served in memory:
1 Mb (With modification - 16 Mb);
Number ext. Timer interrupt: 2;
Frequency ext. Timer interrupt:
30 Hz - 1.75 MHz;
Now the pure theory: Chip i8237A (i8237A
-4, I8237A-5 analogue - KR1810VT37) has 4
independent (!) DMA channels, ie each
channel can work with your sampling! Works under the scheme,
with frequency 3.5 MHz (7 MHz, with some modifications
TURBO). PRINCIPLE work is based on direct
memory access (Direct Memory Access -
DMA). Furthermore raspihivaniya samples through it can be used
for other purposes, such as an accelerator for use with blocks
(LDIR in our). The benefit is obvious - 4 clock cycles per byte
(with 3.5 MHz DMA). And You can not just flip the blocks with
an increment of the address, but with a decrement, and also
fill some space in a single byte. Because DMA "see" the RAM is
broken not 16 KB (pages), and 64-kilobyte (banks), you can flip
the data without zamorochek between two pages (assuming that
they are in the same bank).
In DMA USC uses two timer
i8253 (i8254, analog - KR580VI53). Protection Each
timer is on Channel 3, with 6 of them
4 assigned to audio channels. The remaining 2 channel encoder
can be used to its sole discretion, to obtain the interrupt 30
Hz - 1.75 MHz. I note that apart There are 4 additional
interrupt system, they are activated at the end of the sample,
so, for the convenience of writing players.
Also add that playing. Mod'ov
takes only 1000 cycles (9000 peak).
Another "+" DMA USC - it is an opportunity
playing 14 bit. wav'ov on the background, ie
processor is engaged in its affairs. They say a player picks up
a lot on the Amiga time in percent.
(C) F.R.
DMA USC vs DMA SB.
Allow myself to express an opinion or
response (call it what you will) about the article ALCo
"DMA Sound Blaster" from the magazine ZX-Guide # 2.
And try to dispel the "fog sayings"
Author not appropriate DMA UltraSound
Card.
The very development of DMA SB interesting and apart from
the illustrations for laboratory work on Electronic entitled
"Device DMA, may be competitors and covox'u SounDrive, but no
more. Why? We will understand with the response, cited by the
author of the article: playback. mod'ov frequency mixing 16
KHz. Sorry, but I Covox (without any extension of the screen)
progryvaet. mod with the same quality. And hardly a TURBO
can hang player. mod'ov on
interrupt, if we consider that the acceleration on
simple PENTAGON'e no more than 1.5 times.
Why the author did not mention the monstrous devaysom GS?
After all, there m / s is not less than DMA USC, and the
arguments generally willing to wait desired. And yet the
author's dictum that on the Speccy not need to hang such device,
as DMA USC. Sorry, but after all why we
then the city 512 KB, digitizers, modems?
Let's go back again in the "cave" and will
listen. mod'y and. wav'y phone quality covox'e and DMA SB?
Lnchno me, actually I do not want to see how the echidna and
amizhniki petseshniki gloat over "Bipernogo sound." Finally did
it then time to assess the quality of the DMA
USC came pisishniki and after proslushvaniya
Mouzon said: "Indeed, SB sounds
worse! ".
And yet, ALCo writes: "... during his (in
sense DMA USC) work can not be used
MultiColor bordernye and effects. "I wonder what did he mean,
can that DMA SB is it possible? Brad! Anyway
If his views erroneously! You can simply
DMA USC at work at the frequency of 44 KHz comp
slows down for a maximum of 5-6%. And all
normal demomeykery be doing demos in their installer, which
automatically adjusts to any speed of PC.
And about programming SB and say terrible, not only is a
fixed frequency - 16 KHz, but for samples of the need to cut
into pieces of 16-192 bytes and shove it all across the memory
according to the company structure of the screen. Hmmm ... no
words.
And in general Speccy done in order to
He lived (!). And not for the fact that it cut all the tracks
and yuzali ULA as SaundBlaster.
Communication.
As mentioned above, questions can be sent to the newspaper
ZX-Pilot, if Do you live within the city Kovrova or
in my mailbox (it's faster
way):
85280 Ukraine,
Donetsk region.,
Dzerzhinsk,
P. Kirov,
st. Youth, 16/48,
Mihalchenkovu Dmitry
aka Hard.
Questions can send in handwritten
as well as electronically, on diskette. Return discs guarantee,
although if you're with disk send a little money on postage
costs, it will accelerate much.
