DMA Ultrasound Card

Unlike the more popular General Sound card, DMA USC is not a separate microprocessor system. It is built on the basis of the direct memory access controller ( DMA ) КР1810ВТ37 (Russian analogue of the i8237 chip), and uses the main memory of the computer to store sound samples. The KR1810VT37 microcircuit provides the implementation of four separate channels of direct access to memory, which makes it possible to simultaneously transmit four data streams from memory to separate 8-bit DAC cards. The transfer speed for each channel, and hence the playback speed of the samples, is set using two programmable three-channel timers KR580VI53 (i8253). At the same time, the main processor of the computer sets the transfer parameters, and the sound itself is played without its participation. However, since the main address and data buses are used for forwarding, sound reproduction slows down the computer, pausing the processor for the duration of data sampling. This process takes much less time than with fully programmed sound playback (as, for example, with a SoundDrive device), leaving enough processor resources to run any program. A MOD music player takes on average 5-15% of the system time at a standard clock frequency (3.5 MHz ), which is comparable to the time spent by some music players for AY-3-8910 .

In addition to playing sound, the card also provides some additional features not available on regular ZX Spectrum-compatible computers. These are fast block transfers of data inside the computer’s memory without the participation of the processor and generation of processor interrupts with a programmable frequency (in the standard ZX Spectrum there is an interrupt only at the beginning of the frame display, with a frequency of 50 Hz ).

DMA USC connection requires serious intervention in the computer circuitry. Being connected, the card significantly changes (extends) the architecture of the ZX Spectrum. To ensure the possibility of such a connection, it is supposed to make changes and perform modifications to the computer circuit. Since the circuitry of various versions of Russian ZX Spectrum-compatible computers can vary greatly, connecting the card to many of them is impossible without special knowledge. The connection instructions were developed only for Pentagon computers with RAM expanded to 512 KB, and KAY-1024 . For normal operation of the card, the main RAM of the computer should have a capacity of 512 KB or more. The card could work with the standard 128 KB, however, this did not make sense due to the insufficient amount of memory for storing the program and sound data. So the average music file in MOD format exceeded 100 KB, which already created certain problems for PC users with a RAM capacity of 128 KB if you wanted to listen to such a file.

Many spektrumistov who collected the card, had a desire to put the DMA USC in turbo mode (7 MHz ), which could increase the speed of operations with memory units (transfer memory-memory) by 2 times, but in this case there could be problems with unstable operation Russian chips KR580VI53 at an increased frequency. To solve the problem, it was recommended to replace them with the original i8253.

The view that adapting existing software for DMA USC is noticeably more complicated than adapting for General Sound is not true. For DMA, the software written for COVOX and Sound Drive is most easily adapted; just replace the playback subroutine. In the case of games that did not support either the 128kb mode or music coprocessors at all, the scoring task was completely elementary and comparable to the adaptation for General Sound.

The developer of DMA USC (Alexey Inozemtsev / Stranger), as well as the Witchcraft Group (Andrey Mikhalchenkov / Fr and Dmitry Mikhalchenkov / Hard) developed and adapted a number of programs for the card. Among them:

• Access Player v1.2 - a player for MOD files that supports working with floppy disks in MS-DOS format. Program author Alexey Inozemtsev / Stranger.
• Digital Studio v1.12 is an adapted version of the popular music editor. Adapted by Alexey Inozemtsev / Stranger.
• ProDigital Editor is an adapted version of the music editor. Adapted by Alexey Inozemtsev / Stranger.
• Free Speed ​​Utility - a utility for changing the speed of a computer. The author of the Witchcraft Group program.
• Witchcraft Resident Boot Installer is a utility for installing a diskette loader that resides in the computer’s memory and is instantly launched by pressing the NMI (Non-maskable interrupt) button. The author of the Witchcraft Group program.
• X-Tracker 0.4 - music editor, MOD format
• Mixer 1.5 - a utility for mixing sound effects. Adapted by Alexey Inozemtsev / Stranger.

And also adapted versions of games:

• Barbarian 3
• Wacky darts
• Fist 1
• Dizzy 2
• Rambo 2
• Joe blade 3

• Sampling frequency : theoretically up to 3.5 MHz (not kHz), practically up to ~ 200 kHz
• Sound channels: 4 independent 8-bit channels with their own DACs
• Volume control: 4 independent 6-bit volume controls, one for each channel
• Supported memory capacity: up to 1 MB (expandable up to 16 MB)
• Maximum Continuous Sample Size: 64 KB
• Additional features:
  • Interrupt generation for the main computer processor with a frequency of 30 Hz to 1.7 MHz
  • Fast transfer of memory blocks, including inter-page transfers
  • The ability to change the speed of the computer in the range from 50 to 100%

Due to the low prevalence of the device, and the very small amount of software that uses its capabilities, DMA USC is currently not supported by any of the ZX Spectrum emulators.

• “Your Computer” No. 4-6 of 2000

• The Witchcraft Creative Group is the site of the group that developed the DMA USC.
• DMA UltraSound Card
• DMA USC (link unavailable)
• DMA Ultrasound Card