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Common Microcode Finite State Machine for Driving Both an Enhanced Small Disk Interface and an ANSI 3.8 Interface

IP.com Disclosure Number: IPCOM000035913D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28

Publishing Venue

IBM

Related People

Farrell, JK: AUTHOR

Abstract

This article describes a common microcode finite state machine (FSM) which is capable of driving both an enhanced small disk interface (ESDI) and an ANSI 3.8 interface.

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This is the abbreviated version, containing approximately 28% of the total text.

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Common Microcode Finite State Machine for Driving Both an Enhanced Small Disk Interface and an ANSI 3.8 Interface

This article describes a common microcode finite state machine (FSM) which is capable of driving both an enhanced small disk interface (ESDI) and an ANSI
3.8 interface.

It is not uncommon to find different interfaces being supported on a single storage subsystem adapter today which must support a di

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rect access storage device (DASD) and diskette devices. The microcode resident in the adapters must manage these different interfaces which essentially provide the same function to the host system. The devices attached to these interfaces essentially possess the same function. For this reason it is possible to isolate the hardware interface of these different interfaces and search for a common function in order to develop a common microcode state machine. A common state machine translates to common microcode with a reduced code development effort and long term code maintenance consolidation. Such a common microcode FSM is described herein.

The most common and obvious functions which must be supported by DASD and diskette devices attached to these interfaces are format, read, write and verify. More specifically, the finite state machine of this disclosure manages the physical device and data buffer for

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request from a host system which can exceed the size of the data buffer available in the adapter for the read, write and verify functions.

Fig. 1 shows the general hardware configuration of the storage adapter that the FSM is described for. The hardware environment shown is in its simplest form, only showing the major components necessary to begin a discussion of the FSM.

The storage adapter is shown within the broken-line box and is attached to the system bus along with the main processing unit (PU) and PU memory. The FSM resides in the box labeled "RAM CODE", and executes on the micrprocessor in the storage adapter. The main job of the FSM is to manage the floppy drive attached to the ANSI 3.8 interface and the hard drive(s) attached to the ESDI interface. In addition, the FSM manages the RAM data buffer which is an intermediate storage area for sectors which are read, written or verified from/to the devices. Data transfer occurs between the RAM data buffer and the drives through these interfaces. In addition, the FSM manages the

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data transfer between the PU memory and the internal storage adapter's RAM data buffer.

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Each device has a dedicated portion of the RAM data buffer for exclusive use called a device data buffer. The size of a device data buffer is selected based on performance requirements and expected sector size data distributions of the storage subsystem. Because of these factors the device buffer is sized to satisfy the typical sector size data distribution requests from the PU. A 4K-byte RAM data buffer size will be used herein for illustration purp...