The Itsy Pocket Computer

The Itsy Pocket Computer is a flexible research platform, developed to enable hardware and software research in pocket computing. It is a small, low-power, high-performance handheld device with a highly flexible interface, designed to encourage the development of innovative research projects, such as novel user interfaces, new applications, power management techniques, and hardware extensions. There are several versions of the basic Itsy design, with varying amount of RAM, flash memory and I/O devices. We used several units for this study that were modified by Compaq Computer Corporation's Western Research Lab to include instrumentation leads for power measurement. Figure 1 shows the units along with the measurement equipment we used. We investigate the energy and power consumption of the Itsy Pocket Computer when it is run at between 59 MHz and 206 MHz, and when its StrongARM SA-1100 [9,10] processor is powered at two different voltage levels.

Figure 1: Equipment setups used to measure power.

All versions of the Itsy are based on the low-power StrongARM SA-1100 microprocessor. All versions have a small, high-resolution display, which offers $320 \times 200$ pixels on a 0.18mm pixel pitch, and 15 levels of greyscale. All versions also include a touchscreen, a microphone, a speaker, and serial and IrDA communication ports. The Itsy architecture can support up to 128 Mbytes both of DRAM and flash memory. The flash memory provides persistent storage for the operating system, the root file system, and other file systems and data. Finally, the Itsy also provides a ``daughter card'' interface that allows the base hardware to be easily extended. The Itsy uses two voltage supplies powered by the same power source. The processor core is driven by a 1.5V supply while the peripherals are driven by a 3.3V supply. Both power supplies are driven by a single $3.1V$ supply connected to the electrical mains.

Figure 2: Itsy System Architecture

The Itsy version 1.5 units used as the basis for this work have 64 Mbytes of DRAM and 32 Mbytes of flash memory. These units were modified to allow us to run the StrongARM SA-1100 at either 1.5 V or 1.23 V. Although 1.23V is below the manufacturer's specification, it can be safely used at moderate clock speeds and our measurements indicate the voltage reduction yields about a 15% reduction in the power consumed by the processor; the percentage of power reduction for the system may be less than this (depending on workload) because voltage scaling only reduces the power used by the processor. The Itsy can be powered either by an external supply or by two size AAA batteries. Figure 2 shows a schematic of the Itsy architecture.

The system software of the Itsy includes a monitor and a port of version 2.0.30 of the Linux operating system. The Linux system was configured to provide support for networking, file systems and multi-user management. Applications can be developed using a number of programming environments, including C, X-Windows, SmallTalk and Java. Applications can also take advantage of available speech synthesis and speech recognition libraries.