A 21st Century Sea Change Taking Place in Embedded Microprocessors
David Guzeman, Chief Marketing Officer (acting),
IntellaSys Corporation, Cupertino, CA
It has been 30 years since the 8048/8051 microprocessors appeared on the market and changed the world's view of what an embedded microcontroller should look like. Over the years, each new microcontroller has tended to follow that basic architecture, adding improvements at each step in order to stay in step with the increasingly demanding applications. As long-lived and important as that original architecture has been, it is now time to embrace a new multicore architecture, one designed from the ground up to handle the applications of the 21st century. In this white paper, we will discuss the sea changes in architecture design that are being driven by demands for higher operating speeds and lower power dissipation.
20th Century Applications
The typical application from the 20th century used an 8-bit microcontroller — a bit banger &mdash that could read sensors, do a small amount of data processing, and then drive some I/O lines, probably parallel, in order to send characters to a display or record a data byte onto tape or some other data logging device. Additional I/O lines could scan a simple keyboard or set of switches, and the whole thing could be driven within time constraints by an on-chip real time clock that could provide precise timing references to sync data transfers, and perform other time-driven tasks.
These applications used only a small amount of memory, perhaps 64 to 256 bytes of RAM, and most of that was integrated on the chip. Although provisions were made to access external memory as well, this was initially a primitive interface consisting of just an address and data bus and relied on the processor to read and move data in and out of external memory under software control.
Thus the emphasis was on controlling I/O within tight time constraints with very little actual data manipulation done by the processor chip. That's fortunate because the processor was extremely limited in its data processing capability anyway and was very slow running at clock rates of a few Megahertz. As limited as these chips were, they were sufficient to control countless simple applications ranging from wall thermostats to simple home automation systems. In fact, at this moment I'm typing this paper on a recently introduced laptop that uses a derivative of that original 8048 chip for the sole purpose of reading keyboard clicks. Over time, processors were introduced that were even smaller with less capabilities that sold for, presumably lower prices. At the same time, others came out that were more advanced, both 16 and 32 bit versions, and with much faster and more sophisticated external memory interfaces using DMA controller circuitry. Still, the basic idea has remained the same. One or two processors on a chip, reading data from input lines and sending data to output lines, and wiggling I/O control pins as appropriate… all to the metronome of an external reference real time clock.
Consumer Electronics is Driving 21st
Century Applications
But now the nature of the applications has changed dramatically. In addition to the traditional real time bit banging, a new dimension of processing capability has been added — the processing of algorithms. Today the high-volume applications are multimedia consumer aps that range from tiny MP3 music players to cell phones with video capability. Moreover, the long awaited avalanche of high-definition televisions has begun, and along with those televisions, consumers are suddenly perceiving the need for home networks that move video and music from room to room.
Multimedia Capability
All new consumer applications have digital data at their heart, and that implies extensive digital signal processing in any device that displays or plays that data. The various file formats for multimedia have been carefully designed with an eye toward digital processing by using mathematical algorithms — Fast Fourier Transforms (FFTs), discrete cosine transforms (DCTs), and so forth. The high bandwidth required to serve multimedia applications requires that 21st century processors have dedicated circuitry for processing those algorithms. But at the same time, none of the earlier requirements for general purpose I/O and real time clocks has gone away. New chips must handle both!
Bitstream Orientation
Whereas earlier processors viewed external memory as the source and destination of applications data, modern processors must be able to operate with high-speed bitstreams of data arriving from the internet, USB and 1394 cables, as well as cable and satellite television services. The USB 2.0 interface, now nearly ubiquitous on consumer products such as cameras, MP3 players, and even cell phones, requires up to 480 mbit/sec. The 1394 interface is commonly used in video applications and comes in 200/400/800 mbit/sec rates. Even gigabit Ethernet is beginning to appear in homes with even higher data rates yet. Today's processors have to deal with these data rates, all of which are staggeringly fast by 20th century standards.
To make matters worse, the new High Definition Audio-Video Network Alliance (HANA) standard for home networking assumes up to FOUR 1394 bitstreams that may reach 800 Mbit/sec. And MP4 formatted data assumes multiple bitstreams for audio and video plus optional additional streams for things like subtitles and still images. In many cases, the same processor that is decoding the MP4 bitstream from a buffer memory must also handle the incoming bitstream as well, so that as many as four or five of these high-speed bitstreams must be handled at once.
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