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MS DOS Device Drivers

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

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MS DOS Device Drivers

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  1. MS DOS Device Drivers • Sources of Information • Device driver basics • Structure and internal routines

  2. 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

  3. 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

  4. General Structure

  5. Device Header • 18-byte block at beginning of every device driver

  6. 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

  7. 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

  8. Sample Command Codes • 00H: Driver Initialization • 01H: Media Check • 04H: Read • 08H: Write • 0DH: Open • 0EH: Close

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