International Appliance Manufacturing 2008 - (Page 41) markets, there are already a variety of solutions supported by operating systems derived from the desktop and powerful applications processors. But, what about the embedded control engineer who runs his code on bare metal with no operating system or maybe just a simple RTOS kernel? He might be tasked with designing a new washing machine, coffee maker, microwave, copy machine, spa or other consumer product that is often driven by one or more small processors. In this embedded control space, 8-bitters continue to dominate in unit sales because performance is still adequate for many appliances. They are also cheaper and simpler to use than 32-bitters. But, when the 8-bit microcontroller reaches its limit in performance or memory addressing capability it is time to consider an upgrade to a 16- or 32-bit microcontroller. A full color interactive GUI is one of those applications that exceeds the memory addressing of 8-bit processors and is therefore an opportunity for migration to ARM ® . Because of their low prices and high peripheral integration, microcontrollers based on the ARM7TDMI are positioned very well as the perfect stepping-stone from the 8-bit world to the 32-bit world. But, obstacles still exist if the ARM7™ is to fill the gap between the 8-bit user interface and the 400 MHz multimedia processor. First, the memory bandwidth of the ARM7 needs to be boosted to accommodate the display refresh requirements of full color LCD displays. Second, desktop style operating systems do not run on the ARM7 processor. This leaves a gap in both the firmware and development tools required to deliver an attractive GUI on the ARM7. Let’s try to understand the first concern – memory bandwidth. In most embedded GUI applications, the required amount of frame buffer memory is so huge that it is not cost-effective to put it on the controller. For example, a 24-bit color VGA (640x480 pixels) LCD requires a frame buffer of 1.2 MBytes. A microcontroller with this much internal SRAM would be prohibitively expensive, so the frame-buffer must be stored in external RAM. In addition, consider that the minimum refresh rate for an LCD display is typically 60 frames per second. This means that the CPU needs to fetch 1.2 MBytes of data 60 times per second, or 73 Megabytes per second. Even at 80 MHz, a conventional ARM7 processor cannot possibly achieve this level of throughput. But, with the combination of a multi-layer bus matrix and two independent memory systems, the memory bandwidth problem can be overcome. Amulet Technologies, a fabless semiconductor companying specializing in User Interface Controls, offers a single chip solution based on Atmel® Corporation’s CAP™ customizable microcontroller. Amulet’s patented Graphical OS in Silicon™ technology runs on Atmel’s CAP7 platform bringing the appliance designer 24/7 reliability, flexibility and cost savings. Off-the shelf, single chip solutions, are available from Amulet Technologies and most likely have everything you need for your appliance controls, however, CAP7 creates a flawless platform for designers to pull together additional application specific IP. For example, designers can now easily pull in different GUI pieces, such as capacitive touch, force feedback, USB etc., and other non-GUI third party IP is also available at no cost from Atmel. This intriguing design allows an ARM7-based CAP microcontoller to control userfriendly embedded systems, such as household appliances, that would otherwise require a more powerful microcontroller. Because the demand for screen refresh exceeds the ARM7TDMI processor’s bus bandwidth, Amulet’s custom logic offloads that task from the CPU. This frees the ARM7 core to run the application code without interruptions from the screen refresh. The Amulet LCD controller can drive passive monochrome or color LCDs with resolutions up to 640 x 480 pixels, or color TFT LCDs with resolutions up to 800 x 600 pixels. It handles all refresh tasks and has an internal frame buffer sufficient for small displays. Larger screens require an external frame buffer in SDRAM. As shown in the block diagram of Figure 1, Amulet’s GUI Engine accesses the frame buffer directly International Appliance Manufacturing 2008 41
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