Emerson MVME147 Writing A Driver, Scsi_Cmd, Scsi Actv, Scsi_Int, Scsi_Fun, Scsi_Ca, Scsi_Rte

WRITING A DRIVER

5

Introduction

This chapter covers information essential in writing a driver to support the SCSI interface in interrupt mode. A driver for non-interrupt mode is a trivial subset of the interrupt mode driver. The approach taken is to describe the major sections of a driver that need to be written. The examples shown have been extracted from the VERSAdos SCSI driver, and are dependent on the driver interface to the VERSAdos operating system. For this interface, see Figure 5-1. For details of the interaction between the driver and the SCSI firmware, see Figure 5-2.

Any driver that communicates to the SCSI firmware starts by building (for single callers) a command packet in memory and calling the command entry point SCSI_CMD in the MVME147Bug. The address of the packet is contained in register A2.

Access to the six SCSI entry points is provided through the use of a jump table located within the beginning of the MVME147 debug monitor. The jump table entry points and their SCSI firmware functions are shown in the following list.

SCSI_CMD	EQU	$FFFE077C	SCSI command entry.
SCSI_ACTV	EQU	$FFFE0782	SCSI command
			reactivation entry.
SCSI_INT	EQU	$FFFE0788	SCSI interrupt entry.
SCSI_FUN	EQU	$FFFE078E	FUNNEL command
			entry.
SCSI_CA	EQU	$FFFE0794	Come-again entry.
SCSI_RTE	EQU	$FFFE079A	RTE entry.

Interrupts from the SCSI controller chip are through vector $45 (offset $114). Interrupts from the MVME147 SCSI DMA channel are through vector $46 (offset $118). The self interrupts from the MVME147 SCSI firmware use the vector $4B (offset $12C) to return control to SCSI firmware. The SCSI firmware sets these vectors to point to its interrupt entry point.