Combine the GX1 Pentium processor core from National Semiconductor with a 2D video controller and you have the heart of the SC1200, SC2200, and SC3200 system-on-a-chip (SoC) devices. The main difference between the chips in the SC product line are additional peripherals and the video support targeting the chips to fit specific applications, such as thin client PCs.
Alternate solutions abound, but National Semiconductor's approach is the first to bring Pentium power to bear in a single-chip approach. Products like ZF Linux Devices' MachZ PC-on-a-chip incorporate a 486 core and leave the video to an external device. Still, the MachZ incorporates the flexible FailSafe boot that National Semiconductor's line includes.
Although a variety of RISC-based solutions are available, they don't have the same level of support as the x86 architecture. Broader support may be important for applications like thin client PCs where existing x86 applications are available and well tested. Operating systems for the product line are available from Be Inc., Bsquare, Infomatic, Insyde Software, Lineo, Merinta, Microsoft, and QNX, with more undergoing testing.
The x86 architecture and development tools also are well known by designers. Likewise, the SC product line incorporates familiar PC-compatible interfaces, such as USB. Plus, IDE allows migration from multichip x86-based solutions.
The GX1 core includes a Pentium-class processor with MMX support, a 16-kbyte level-1 cache, a 64-bit SDRAM memory controller, and the 2D video accelerator (see the figure). The core is shown as part of the SC1200. It's employed in the other two chips in the SC product line as well. This architectural consistency allows designers to choose the appropriate chip with minimal software changes to accommodate the hardware differences.
The processor speed currently tops out at 266 MHz. This is more than enough horsepower for the intended applications. Likewise, the 2D video accelerator provides enough features and power for most applications except games that might require a 3D video accelerator. The need for different products is primarily due to differences in audio and video peripheral support. In general, the number of support chips necessary for a particular application is kept to a minimum.
Building an Internet set-top box just became easier with the SC1200. The key additions are the video input port and the NTSC/PAL-compatible video overlay processor.
The other peripheral controllers are those found in a standard PC, such as the IDE ATA-33 controller, a USB controller, an AC'97 audio controller, and a parallel port, as well as serial interfaces, one with infrared support. Of course, external PCI and ISA peripherals can be included too.
Minimal peripheral support is needed for infrared devices like keyboards. Software and external hardware provide plenty of ways to differentiate products based on the SC1200.
In order to utilize the SC2200, swap a television in the design for a flat-panel display or monitor. This sounds a bit like a low-end or thin client PC. The SC2200 replaces the SC1200's video overlay processor with a video interface that can drive up to a 1024-by-768 TFT flat-panel display or a VGA monitor. This platform is effectively a conventional PC-on-a-chip.
The primary limitation of choosing a single-chip solution like the SC2200 is the ability to upgrade to a higher-performance processor. Luckily, this is the realm of a full-blown PC and not PC products targeted by the SC2200. This is no different than requiring a better video controller.
Portable devices typically require an LCD that an SC2200 could support, but rarely will these applications require a VGA connection. The SC3200 eliminates the VGA support while retaining the rest of the SC2200's PC compatibility.
It's more than likely that designers employing the SC3200 will make selective use of the built-in peripheral controllers other than the video support. USB will probably find a use in most applications, but a parallel port tends to require a rather bulky connector.
One component that still resides outside of the SC product-line integration is an Ethernet controller. National Semiconductor has an Ethernet/Home Phoneline Network Alliance (PNA) controller in addition to a 3COM 10/100BaseT-based controller.
National Semiconductor's x86-integration approach isn't unique, even though the performance and peripheral combinations are new. VIA Technologies Inc. will implement a two-chip ap-proach with much of the peripheral support in the Southbridge chip. This provides a better mix-
and-match approach, yet it doubles the primary chip count and increases the interconnect complexity.
The company's approach will have a significant impact on designers familiar with the PC's x86 architecture and tools. Software prototyping simply requires a PC in most cases, significantly reducing development costs. RISC-based solutions often provide software emulation support. Still, in addition to the cost of the emulator, emulation results in slower performance than running on hardware.
There's generally a lack of royalty tools and operating systems, like Linux, available on the x86 platform. This further reduces development costs. In the past, using an x86 platform for embedded applications was cost prohibitive. Chips such as the National Semiconductor SC product line remove this limitation.
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