Sim-iPAQ

A SimpleScalar-based Platform Simulator for the iPAQ Computing Environment

The following is the first release of the SimpleScalar iPAQ platform simulator. It is capable of booting the Linux operating system and provides a root filesystem with a variety of useful ARM Linux utilities.  Comments, questions, or bug fixes may be directed to the authors via email at ss-sa@cs.colorado.edu.

In this release, the critical platform components have been implemented including ARM instruction emulation, ARM MMU support, and I/O models for the ARM iPAQ real-time clock, interrupt controller, serial devices, FLASH and DRAM memory, and the OS timer.  The simulator model is able to boot the Linux kernel; however, some bootloader and Linux commands are still not functioning due to a few remaining implementation issues. Nevertheless, a significant amount of functionality exists in this release, therefore we have made it available and will update the code as bugs are identified and fixed.


1  Sim-IPaq Distribution Components

Platform Simulator - The platform simulator is derived from SimpleScalar version 3.0 located at www.simplescalar.com.  It includes ARM instruction emulation, ARM MMU support, and I/O models for the ARM iPAQ real-time clock, interrupt controller, serial devices, FLASH and DRAM memory, and the OS timer.

Platform Console - The platform console provides serial terminal emulation.  It connects to the platform simulator and allows the user to issue bootloader and Linux command-line commands to the simulator.

ARM Bootloader - The ARM bootloader is installed into memory at simulator initialization time.  It decompresses the kernel and initializes the filesystem.

ARM Linux Kernel - The ARM Linux Kernel provides operating system functionality and is decompressed by the bootloader at initialization.

ARM Linux Root Filesystem - The ARM Linux Root Filesystem provides a number of standard utilities in the root filesystem that are available after the ARM Linux Kernel boots on the platform simulator.  A few examples of these standard utilities are ls, diff, and mount.

2  Building the Simulation Environment

The following sections will describe how to build the various components of the Sim-iPAQ simulation environment.  One thing to note before beginning is that this release of Sim-iPAQ has only been tested on RedHat Linux version 8.0 for x86.  However, it will probably work on any little-endian platform provided that the build uses GNU GCC for the compilation.

 
2.1  iPAQ Platform Model

The Sim-iPAQ platform model, located in the "sim-ipaq/" directory of the download archive, must be configured before it can be built.  In addition to the normal SimpleScalar configuration parameters found in the README file, the variable LINUX_PATH in the Makefile must be set to the root location of the Linux build.  Once the normal configurations are made and the Makefile is configured as above, the platform simulator, called sim-ipaq, is built with the following command:

make

The build processor will also compile the Platform Console, conveniently called console.


2.2  iPAQ Bootloader, ARM Linux Kernel, and Root Filesystem

Before beginning with this step, it should be noted that pre-built versions of the iPAQ Bootloader, ARM Linux Kernel, and Root Filesystem are provided in the Sim-iPAQ distribution, thus you may skip this step unless a custom kernel or filesystem is required.  

If a custom environment is desired, the first thing that will be needed is an ARM cross compiler to build the bootloader and ARM Linux Kernel.  One such cross compiler is available for SimpleScalar at the following location:  http://www.simplescalar.com/v4test.html.

The iPAQ Bootloader, located in the "linux-build/bootldr" directory, is a free ARM-based bootloader distributed by Compaq.  It provides a variety of debug functions, plus Linux kernel decompression, and root filesystem initialization.  To build the bootloader execute the following command in the bootloader directory:

make

This will produce the file "bootldr.bin", which is an ELF binary format bootloader, in the format expected by the Sim-iPAQ platform simulator.  See the README files for details on the commands supported by the bootloader.  Additional documentation is available by executing the "help" command at the bootloader prompt.

The ARM Linux Kernel, located in the directory "linux-build/linux", has a complete kernel build.  A large number of build options are available for the kernel which can be seen in the README file located in the above linux-build/linux directory.  The kernel has been pre-configured with the options expected by the Sim-iPAQ platform simulator.  To build the ARM Linux Kernel, execute the following command in the kernel directory:

make zImage

This will create "zImage.bin", which is a compressed ARM Linux Kernel with devices compiled in to match the devices supported by the Sim-iPAQ platform simulator.

The ARM Linux Root Filesystem provides a minimal filesystem available to users once the ARM Linux Kernel boots on the Sim-iPAQ platform simulator. The root filesystem is loaded into simulated FLASH memory as a compressed-RAM filesystem (CRAMFS).  The first step to building a compressed-RAM filesystem is to build the filesystem build utility "mkcramfs", which is located in the directory "linux/kernel/scripts/cramfs/".  Build this utility with the following command in the CRAMFS directory:

make

Next, assemble a filesystem, on the local host filesystem, with exactly the same ARM binaries and permissions desired on the CRAMFS. To create the CRAMFS filesystem, execute the following command:

linux/kernel/scripts/cramfs/mkcramfs init-2-56 init-2-56.cramfs

Where "init-2-56" is the top-level directory of the local representation of the filesystem to create, and "init-2-56.cramfs" is the name of the file that will contain the compressed filesystem.


3  Running the IPAQ Platform Model

To run the IPAQ platform model, first run the platform simulator, located in the "sim-ipaq/" directory, with the following command:

sim-ipaq linux-boot

The argument "linux-boot" indicates that the platform simulator should initiate a standard Linux boot sequence.  The standard boot sequence accesses files in the directory specified by the build parameter LINUX_PATH. The sequence first reads the bootloader executable "bootldr.bin", then the compressed Linux ARM Kernel "zImage.bin", and finally the root filesystem "init-2-56.cramfs".

After reading the FLASH ROM components into simulated FLASH RAM, the
platform simulator will connect to the terminal emulator.  The terminal emulator is the user's access point to the Linux simulation, providing a means for entering command lines to the bootloader and Linux shells.  The platform console is a front-end to the serial device emulator.  To start the platform console, enter the following command in a separate window:

console -s script-boot.txt

This will initiate a platform console connection to the running sim-ipaq simulator, and run an initial set of bootloader commands, listed in the file "script-boot.txt".  These commands are required to initialize the Linux kernel memory and CRAMFS filesystem.  Once the commands complete, the Linux kernel will boot, after which the user can enter additional commands from the platform console window.