Paula (Amiga)
Paula is one of the Amigas' custom chips and is responsible for controlling the floppy disk drives , the serial interface and the audio output.
Commodore has revised and improved all custom chips for the AGA chipset. Only Paula was taken over unchanged from the older models.
Sound output
The audio portion of Paula can simultaneously on four voices (stereo, two left, two right) 8 Bit - Samples spend. The sampling rate is always an integer part of the system clock and can (when operated with Direct Memory Access (DMA)) depending on the chipset up to 28 kHz ( Original Chip Set (OCS)) or 56 kHz ( Enhanced Chip Set (ECS) in the VGA Mode). A hardwired reconstruction filter was installed outside the chip . Depending on the Amiga model, this has a cut-off frequency in the single-digit kilohertz range and can partly (together with the status display LED - both functions share one control line) be bridged or switched over by software.
The limitation of the sample rate is due to the nature of the OCS, whose DMA timing does not provide for a higher data rate. If the software sets a higher sampling rate, this only results in the same sample being output multiple times. Since the output register can be supplied with audio data not only via DMA, but alternatively also from the processor (CPU), higher sampling rates can only be achieved by CPU control - with correspondingly high CPU utilization . With the ECS , a higher sampling rate than 28 kHz is also possible via DMA. By coupling the DMA control with the video timing, this is only possible at a higher line frequency ; in VGA mode up to 56 kHz. If the ECS is set to a conventional television video mode with a 15.625 kHz line frequency, it can, like the OCS, only provide data for a sampling rate of 28 kHz.
Although the individual channels only offer a resolution of 8 bits, it is quite possible to increase the resolution to 14 bits by cleverly combining two channels. Due to hardware tolerances in the D / A converter , the quality is inferior to that of a real 14-bit resolution. With appropriate calculations by the CPU, it is also possible to increase the number of channels on the software side. The trackers Octalyzer and OctaMED , which each offer eight channels, were known for this .
Since competing computer platforms only provided very rudimentary sound output via system speakers or expansion cards at that time , the Amiga and its Paula chip offered a simple way of composing sample- based music. Together with the MOD file format , this explains the popularity of this IC.
Interface to the floppy disk drive
Paula is still responsible for reading and writing DD disks. The chip cannot provide the data rates of around 500 kilobits per second required for conventional HD floppy drives. Therefore, Amiga models with HD drives contain a special drive that rotates the magnetic disk of HD floppy disks at half the speed, which means that writing and reading is only as fast as with DD disks - i.e. twice as much time as in common (PC) HD drives.
Versions
- 8364R4 ( DIP , A1000)
- 8364R7 252127-02 (DIP, A500 +, A2000, A3000, AA3000, CDTV)
- 8364R7 391077-01 ( PLCC , A600, A1200, A4000, CD³²)
Individual evidence
- ↑ Amiga Custom Chip Paula (English)
