Ms dos device Drivers Sources of Information

MS DOS Device Drivers

• Sources of Information

• Device driver basics

• Structure and internal routines

Sources of information

• John Angermeyer and Kevin Jaeger, MS-DOS Developer’s Guide, Howard W. Sams, Indianapolis, 1986

• Ray Duncan, Advanced MS-DOS, Microsoft Press, Redmond, Washington, 1986

• Robert Lai, Writing MS-DOS Device Drivers, Addison-Wesley, Reading, Massachusetts, 1992

Device driver basics

• Operating System modules that control hw

• Isolate higher levels from hw specifics

• Standard interface with OS

• Installable at boot time as a “chain” (CONFIG.SYS)

• Not necessary to modify the OS

• Similar to Unix/Xenix/Linux device drivers

• Two types: Block and Character

General Structure

Device Header

• 18-byte block at beginning of every device driver

Strategy Routine

• Called by MS-DOS when driver is first loaded

• Called by MS-DOS whenever I/O request is issued to device

• Request call includes a pointer to a request header; driver saves pointer and returns to MS-DOS

• Request header includes command code and other information

Interrupt Routine

• Called after the strategy routine

• Implements the device driver proper

• Performs the actual I/O operations

• Collection of subroutines to implement various functions (read, write, …)

• Centralized entry routine saves registers and sets up driver ops

• Centralized exit routine restores registers and sets status and error codes

Sample Command Codes

• 00H: Driver Initialization

• 01H: Media Check

• 04H: Read

• 08H: Write

• 0DH: Open

• 0EH: Close