Introduction

Prior and Related Work

Hardware / Software

Embeded Xinu Video #1

Embeded Xinu Video #2

Project pictures

Hardware

As our target platform, we have chosen the ubiquitous Linksys WRT54GL family of wireless routers. These routers devices are readily available at inexpensive prices, and can already be found in homes, small businesses, and collegedorm rooms. They contain a little-endian embedded MIPS 32 processor, operating in the 200-300 MHz range, with 16MB of RAM, and 4MB FlashROM. Several versions of the router are available, but all have easily accessible serial port connections on the main board that allow direct access to the device rmware.

 

With only minor modications to the casing and the addition of an RS-232/TTL serial transceiver circuit, the serial console of the WRT54GL becomes accessible to the student.
From the serial console, a user can interrupt the normal boot sequence from FlashROM, and substitute an uploaded kernel image from over the local area network (LAN) port.
Thus, students can quickly nd themselves running their own embedded O/S kernel on the raw hardware, with no emulation or simulation involved. An overview of this processis shown in below figure.

WRT54GL routers are on the upper end of the enormous spectrum of embedded devices available to us; their speci- cations are roughly equivalent to desktop PCs from the early 1990's. Yet, while they are not as resource-constrained as 4- and 8-bit embedded microcontrollers, they are true embedded systems in the modern context. Processor speed and RAM size are orders of magnitude less than typical desk toPCs, and input/output channels to the processor are narrow.

They are missing major components that would be found in non-embedded contexts { no hard disk or optical storage, no video adapter, mouse, or keyboard. They provide a variety of interesting peripherals (wireless and wired network interfaces, Flash ROM storage, LED and general purpose I/O pins,) but present realistic obstacles to traditional debugging techniques. The highly resource-constrained operating systems they contain are event-driven systems expected to run indenitely with no direct interaction from users or administrators. In short, we feel that they are an excellent choice for prolonged experimentation by students with an interest in embedded computing. As an added benet, they are a RISC architecture commonly taught in lower division computer organization courses, so many students will already have some familiarity with the instruction set.

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