Device Driver Model

To be able to configure the system without recompiling, RDOS uses separate compiled device-drivers. The device-drivers usually have the .rdv extension. Any number of device-drivers can be included in the OS image.

This has several advantages

• Configuration don't need a compiler, linker or locator
• The size of the OS can be reduced / controlled by omitting un-necesary hardware / software interfaces
• Embedded systems can be configured by replacing PC platform drivers with embedded drivers
• Alternative kernels can be used for embedded systems with non-standard I/O addresses for interrupt controller and interval timer.

Installation guide

1. Unpack SRC.ZIP or BIN.ZIP in the directory c:\rdos. It contains the kernel, basic drivers and classlibrary.

System build guide

You need TASM 3.2 to build the OS from the source files. To build the WIN32 DLLs you need TASM 5.0 or later. Pre-built OS kernel (kernel.exe) and device drivers (*.rdv) are included binary release.

Running the OS

You can run the OS in four different configurations

• Boot from a floppy disk
• Boot from harddisk with GRUB bootloader
• Install on harddrive
• Start from real-mode DOS prompt
• PROM it

For convenience, you could start a demo-version of the OS with START.BAT or create a bootable floppy with FLOPPY.BAT, both located in the TEST directory.

Switching between running applications

CTRL + Function key is used to switch between applications. In the demo the following applications could be switched to:

• CTRL-F1 switches to thread list
• CTRL-F2 switches to FTPD.EXE program
• CTRL-F3 switches to DOS prompt
• CTRL-F8 switches to kernel debugger

Debugging kernel and other code

One of my main gools with RDOS, is that everything should be possible to debug. Most of the code can be single-stepped in the kernel-debugger (debugio.rdv). Things that cannot, usually can be debugged in the Intel 486 CPU Emulator.

To debug an device-driver or application do like this

• Put a break-point (int 3 instruction) in the code.
• Build the OS
• Startup
• Press CTRL-F8 to switch to kernel debugger
• Press SPACE to update debugged thread
• Press N to switch among debugged threads
• Press T to trace one instruction
• Press P to pace one instruction
• Press G to run
• Use arrows to select register / address / data to change, and type in the new value.
• Use last row to display Real-mode memory, using segment:offset notation.
• Use next last row to display Protected-mode memory. Here you can also display any linear address by giving selector=20, and entering a 32-bit offset. To display app flat memory use selector 1BB.

To map between protected mode selector:offset and source code do like this:

• Look up the selector name either in protseg.def or driver.def
• Look up the driver file with grep on this selector name
• Look up line number using the map file for the driver.

Note that 30h is the kernel selector, and the related map file is kernel.map