The Programmer's Guide to TRSDOS Version 6 - Tim Mann's Home ...

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2. LDOS VERSION 6 - AN OPERATING SYSTEM OVERVIEW After spending a few hours at any computer show featuring microcomputers, it becomes obvious that most 8-bit machines look surprisingly similar. Each comes equipped more or less with the following features: CRT monitor, keyboard, one or more 5-1/4" or 8" floppy disk drives (usually 5-1/4" minifloppies), 64K-128K of RAM, and a processor card. With the industry seemingly adopting CP/M as an operating system pseudo-standard, the chip usually chosen is Zilog's Z-80 microprocessor. The design of these machines must be sufficiently straight forward. While each competing manufacturer attempts to make its machine more desirable by implementing greater reliability, flexible interfacing, more peripheral support, additional hardware features, attractive packaging, and lower cost, cognizance of the cost effectiveness of utilizing smarter software may just be the important ingredient sometimes overlooked. Alternative operating systems are available that bring a great deal of main-frame power to the microcomputer. One such system, LDOS Version 6 [or its licensed dialects such as TRSDOS 6], is a classic example of a truly powerful operating system designed for an eight bit microcomputer using the Z-80 processor chip. LDOS provides a single-user system with total device independence, dynamic file space allocation, extensive file management, job control language structures, a large library of utilities, plus the ability to easily interface to disk storage devices with capacities from 88 kilobyte minifloppies to multimegabyte Winchester disk drives. Error trapping and an English-like command structure help make LDOS a user-friendly but powerful operating system. The primary design obligation of LDOS is to ensure MEDIA COMPATIBILITY across all machines running the DOS (within the 5-1/4 or 8" size). This means that a user must be able to take a diskette and use it across all machines running LDOS - so long as the hardware permits that size diskette. To accomplish this, the DOS has a "standard" 5-1/4" structure - both single density and double density. It also has a "standard" 8" diskette structure. The structure goes beyond just the format and allocation schemes - it covers the entire directory makeup. The hardware architecture chosen for LDOS Version 6 is a Z-80 based microcomputer with a minimum of 64K RAM and 80 by 24 video screen size. The DOS includes a bank-switching SuperVisor Call that implements memory bank switching. The SVC permits switching a memory segment (usually the top 32K) with up to seven auxiliary 32K memory banks. It also supports the controlled transfer of execution to a location within the bank at the option of the user. The system maintains supervision of the resident bank to ensure that the standard bank (bank 0) is always resident during certain operations (disk I/O, character I/O, and interrupt task handling). The DOS is designed to operate starting from address zero (page 0 origin) and is 100% SuperVisor Call (SVC) accessed. System data items needed by application software are also available via SVCs. Essentially, there are two levels of interaction to the system - command level and primitive level. At the command level, the operator enters a command which requests the execution of some function [perhaps the listing of a file, the displaying of a disk directory, the running of a BASIC program, or the compiling of a C language source file]. The command interpreter parses the user entry, determines whether the request is for a system function or user-supplied function, then arranges for the necessary system resources. Control is transferred to the module necessary to satisfy the request. The system passes parameter pointers to the module and expects a return code upon the module's completion. System resources and data quantities are requested via a SuperVisor Call (SVC) processor. An SVC is associated with all system primitives (i.e. get a character, put a character, open a file, add a task, rename a file, ...). Application software written in a low-level language (such as assembler) makes direct use of the SVC. Programs using a high-level 2-1
language (i.e. BASIC, C, PASCAL, ...) need not bother with the SVC as system interfacing is accomplished within the language interpreter or compiler. The DOS supports up to eight logical disk packs or volumes logically numbered 0-7. Each floppy, be it one or two sided, is treated as a single volume. Hard disk drives (winchesters) may be treated as a single volume or partitioned into multiple volumes. A Drive Control Table (DCT) contains the parameters associated with each disk (number of cylinders, heads, and sectors per track for example) and also interfaces the disk driver software to the system. Character Input/Output devices (i.e. keyboard, video display, printer, RS-232 serial ports, ...) and their associated software driver routines are interfaced to the system via Device Control Blocks (DCB). I/O devices are identified by a two-character device name such as KI (keyboard input), DO (video output), PR (printer), and CL (communications line). Whenever a device is specified, it is denoted by an asterisk followed by the device name to form a complete "device specification". The reason for this will soon become evident. Additional devices can be defined to the system once an appropriate software driver is available. The device name selection is left up to the user. A collection of data stored on disk is termed a file and is denoted by a file specification. A complete file specification consists of five parts: a file name of up to eight characters, a file extension of up to three characters, a file password of up to eight characters, the logical drive specification, and optionally, in certain cases of Partitioned Data Sets (PDS), a member specification of up to eight characters. Whenever users institute a structured naming convention, most files are accessible via the file name reference only. The DOS will search all drives for a file if the drive specification is omitted from the file specification. In addition, many system utilities and user applications can use default file extensions to separate files into classes. For example, PRO-CREATE, a popular assembler running under the DOS, will automatically use the file extension "/ASM" for its source files and "/CMD" for its object code generation thus alleviating the user of the necessity to enter the file extensions (it also helps to prevent inadvertently overwriting one file with another). Similarly, LDOS makes extensive use of default file extensions such as "JCL" for all Job Control Language, "TXT" for ASCII listings, "FLT" for all device filters, etc. File specifications and device specifications are generally interchangeable. Thus, wherever a file specification is needed, a device specification can usually be entered. This is one of the examples of device independence in the system. The protocol used in character I/O is identical across logical devices (i.e. *KI, *PR, *SO,...) and disk files. Thus, character I/O is handled the same way regardless of the physical device identified in the Device/File Control Block (DCB/FCB) - be it physical keyboard, printer, or disk file. For example, the COPY utility is used primarily to copy a file from one disk to another, as in: COPY ARTICLE/TXT:0 TO ARTICLE/TXT:1 which creates a duplicate on drive 1 of the file specified "ARTICLE/TXT" located on drive 0. In lieu of the file specifications, device specifications could equally be used as in the following: COPY *KI TO *PR which copies keyboard input directly to the printer. With ease, a keyboard can be added to a daisy-wheel printer turning it into a temporary typewriter. Perhaps a more useful illustration would be the convenience of directing program output to video display, printer, or a file depending on the device/file specification provided. 2-2
Page 1 and 2: MISOSYS, INC. The Programmer's Guid
Page 3: 1. Introduction Many thousands of u
Page 7 and 8: NAME START END DESCRIPTION LOWCORE
Page 9 and 10: ackup utility provides exceptional
Page 11 and 12: 3. Device Input/Output Interfacing
Page 13 and 14: 3.2.2 VECTOR Field - This field in
Page 15 and 16: FILTER *PR USING *S0 the operating
Page 17 and 18: ===================================
Page 19 and 20: ===================================
Page 21 and 22: ENTRY JR BEGIN ;Branch around linka
Page 23 and 24: DATA1 EQU $-DATA$ DB 0 ;Data storag
Page 25 and 26: Offset Contents +0 Contains the las
Page 27 and 28: image of the serial port UART statu
Page 29 and 30: called TRACKs. Each track is then d
Page 31 and 32: The DCT contains the information re
Page 33 and 34: accessed a single-sided diskette, t
Page 35 and 36: containing the disk's directory. Th
Page 37 and 38: Command Purpose RESTORE Recalibrate
Page 39 and 40: available from Logical Systems, Inc
Page 41 and 42: exceeds this capacity, then it must
Page 43 and 44: is two physical cylinders. Although
Page 45 and 46: 5. The DOS Directory Structure 5.1
Page 47 and 48: ===================================
Page 49 and 50: 5.2.8 PACK NAME - This field conta
Page 51 and 52: The position of a file's hash code
Page 53 and 54: 5.4 THE DIRECTORY RECORD STRUCTURE
Page 55 and 56:
Bit 3 Specifies the visibility; if
Page 57 and 58:
the first granule in use is the sec
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travels the turnpike. In this manne
Page 61 and 62:
The @FSPEC SVC will transfer the fi
Page 63 and 64:
A high level language permits you t
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does exist, @RENAME should return e
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Next, it would be very useful if th
Page 69 and 70:
LD HL,FCBX+9 ;Point to the LRL fiel
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operating system for such a purpose
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position where the last character i
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ecord. If a file has more than four
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DE Contains a pointer to the File C
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@RENAM SVC-56 Rename a file on disk
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@FNAME SVC-80 Obtain filespec given
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@WRSEC SVC-53 Write a disk sector @
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7.6 SUPERVISOR CALL DETAILS 7.6.1 @
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Note: @EXIT in SYS1 automatically r
Page 89 and 90:
7.6.10 @CLOSE SVC-60 This SVC will
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7.6.18 @DCSTAT SVC-40 This SVC pass
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Directory to Buffer Entry: B 1; Fun
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7.6.31 @FLAGS$ SVC-101 This SVC wil
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NFLAG$ This "network" flag is used
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7.6.32 @FNAME SVC-80 This SVC will
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7.6.40 @HEX8 SVC-98 This SVC will c
Page 103 and 104:
7.6.48 @KLTSK SVC-32 This SVC will
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7.6.57 @OPEN SVC-59 This SVC will o
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Registers Affected: AF, BC. Entry:
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0-14 FILENAME/EXT:D - left justifie
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7.6.71 @REMOV SVC-57 This SVC will
Page 113 and 114:
Entry: DE A pointer to the FCB cont
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Exit: A Error return code, if any.
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CURSOR CHARACTER Registers Affected
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Exit: A Will contain the error code
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esident routine into its execution
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CKPAWS LD A,@FLAGS$ ;Get Flags poin
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===================================
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The TYPE=0A indicates that it is th
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Error 08: Device not available A re
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Error 28: End of file encountered T
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8.5 HEADER PROTOCOL OF MEMORY MODUL
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This is obviously an extremely usel
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LD (IX+2),15 JR TASKA By firmly und
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8.7.3 Details of Low Memory Page 2
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actual bank switching. As previousl
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set. Thus, the Z-flag will be indic
Page 145 and 146:
8.10 SYSTEM DISK BOOT TRACK The ope
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14 DEBUG 72 PURGE 1B VERIFY 71 DUMP
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8.13 USING @PARAM The @PARAM SuperV
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DW LPARM+1 DB 'FEED ' ;Line feed pa
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;*=*=* PPARM LD BC,0 ;Zero because
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8.14 TRAP Filter Illustrated ;TRAP/
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8.15 SLASH0 Filter Illustrated ;SLA
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8.16 DMP-500 BOLDFACE Filter Illust
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NOMEM$ DB 'High memory is not avail
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@ @ABORT..........7-2, 7-4, 7-8, 7-
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