User`s manual

Overview

2-6 Single Board Computers SCSI Software UserÕs Manual

Functional Overview

The following sections describe the functional attributes of the Firmware. A

simplistic description of the flow of a command request through the Firmware

is given. The SIOP interrupts are explained in some detail as are the Firmware

responses to various SCSI messages which may be received.

Command Flow

The basic flow of the Firmware is followed as a command request is executed.

This flow should give the reader an understanding of the interdependence

between the MPU code, SCRIPTS code, and SIOP in executing a user request.

The first user access to the Firmware is through a call to siop_init(). The

parameters passed to this initialization call set the operation mode of the SIOP

and Firmware. Interrupt level, snoop mode, clock speed, and SCSI address are

all parameters which are used to program the hardware. Different software

paths are taken if the interrupt level is 0 (polled mode) as opposed to non-zero

(interrupt mode). The Firmware needs to be initialized only once, but may be

initialized many times as long as there are no outstanding command requests

to the Firmware when siop_init() is called.

After the Firmware has been initialized, the user initiates a command to an

SCSI device by passing a command structure (siop_struc) to the command

entry point, siop_cmd(). Some of the fields in the siop_struc which the user

must initialize for all command requests are command control (cmd_ctrl),

device SCSI address and LUN (addr_ilvl and lun), command descriptor block

(cdb), and return status routine pointer (status_ptr). Once called, the Firmware

MPU code performs minimal management operations to enqueue the

command structure (siop_struc) for execution by the SCRIPTS. Additionally,

the user may not alter any field within the siop_struc until the control of the

structure is returned to the user through the invocation of the return status

routine.

From this point, the functional flow of the Firmware differs depending on

whether the interrupt level is set for polled mode or interrupt mode. The

following sections outline the flow for the separate modes.

Interrupt Mode

After the command structure (siop_struc) is enqueued for execution, the

Firmware returns control of the MPU back to the user. All subsequent

Firmware MPU code processing of the user's command request is initiated

through the Firmware interrupt handler entry point, siop_int(). The user calls

this entry point when an interrupt from the SIOP is detected.