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

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entry to maintain the pointers used for each device in the LINK. Several system library commands, such as the FILTER, LINK, RESET, ROUTE, and SET commands, are provided that are used to support device independence. An illustration of the use of these commands lends well to understanding the full power of device independence. For example, if a suitable software driver (with a filename of RS232/DVR) is available for a serial port (RS-232 channel), then a simple: SET *CL TO RS232 will establish the serial port as a device with "CL" as the device name. Now that such a device is available, the user can: LINK *KI TO *CL LINK *DO TO *CL and the micro is established as a "host" because the serial communications line has been linked to both the machine's keyboard and its video display - the primary input and output devices of the machine. Device I/O can also be massaged with transformation functions, called filters. For example, an EBCDIC to ASCII translation filter is available that when applied to the serial port by a simple: SET *XL TO XLATE USING EBCDIC FILTER *CL WITH XLATE the micro can be tied to an IBM mainframe which supports only EBCDIC ports. Want to implement a DVORAK keyboard? By simply filtering the *KI device with the DVORAK translation filter, the keyboard is reorganized - with NO hardware changes required. Many filters are available to format print output, trap specific character codes, perform upper/lower case conversions - the limits are boundless. That's flexibility! Now that you have a flavor of the capabilities of the DOS, this guide can be used to understand how to interface your programs. The bulk of LDOS Version 6 is machine independent. What this means to you as a programmer is that once you write an application to run under LDOS 6.x, it is portable to any machine running version 6. All you need do is utilize the standard interfacing procedures discussed in this programmers guide. Let the DOS do what an operating system is supposed to do - interface the application to the hardware. 2-7
3. Device Input/Output Interfacing 3.1 Device I/O In General Devices interface to the operating system through driver modules. Character-oriented devices (keyboards, video display tubes, printers, and serial terminals, to name but a few), have their drivers connected to the DOS by Device Control Block (DCB) tables [this is in contrast to disk-type devices which have drivers connected to the system through Drive Control Tables (DCT)]. The purpose of the DCB is to associate a device name with the device hardware itself. A device specification (abbreviated as "devspec") is formed by prefixing an asterisk to the device name. Programs may then reference the device via the device specification in order to identify a particular device for character I/O. There are three input/output functions that are associated with all character-oriented devices. The "GET" function obtains a character from the device. The "PUT" function sends a character to the device. The "CTL" function provides a means of communicating with the device driver and generally does not invoke input/output with the physical device itself. It is up to the device driver to ensure that the device is currently able to take the character in the case of PUT as well as detect the availability of a character in the case of GET and return the proper condition. Disk files may also be interfaced via character I/O as well as record I/O [file access via record I/O is discussed in chapter 6, DISK FILE ACCESS AND CONTROL]. A disk file's actual physical storage location on a disk drive is transparent to the user by referencing the file with its associated name (more properly termed its file specification or "filespec"). The operating system permits filespecs and devspecs to be used equivalently in most cases. Character I/O is thus independent of a device or file. The DOS permits the redirection of character I/O at the command level. Because of this, applications must expect character I/O to be associated with a disk file as well as a standard character-oriented device. The DOS provides a uniform protocol for I/O handshaking regardless of character device. There are three major operations associated with devices. One of these is "routing" which implements the support of I/O redirection. Another is linking which is used to connect two or more devices together. The third operation associated with devices uses filters to achieve filtering. Filters are program modules that can be logically placed between the Device Control Block associated with a device and the device driver connected to the DCB. This operation will form what is called a "device chain". More than one filter module may be placed in the DCB-to-driver chain. These filters bear a very close resemblance to device drivers. In fact, they also utilize the Device Control Block tables to associate their memory storage location with the name assigned to them when they are installed. This section will discuss the activities that take place between a Device Control Block and a device so that you will better understand the concepts of character I/O. In this manner, you will have no problem in writing device filters and drivers - at least as far as DOS interfacing goes. 3.2 The Device Control Block The Device Control Block (DCB) is used to interface with various logical devices such as the keyboard, the video display, a printer, a communications line, or other device defined by your hardware implementation. The DCB is composed of eight bytes divided into four fields: TYPE, VECTOR, SYSDATA, and NAME. Figure 3-1 illustrates the DCB. The TYPE field is a one-byte field that describes the capabilities and current state of the DCB (state indicative of routed, linked, filtered, etc.). The VECTOR field is a two-byte field that initially is a pointer to the entry-point of the driver or filter module associated with the DCB. The SYSDATA field is a three-byte field that is used by the 3-1
Page 1 and 2: MISOSYS, INC. The Programmer's Guid
Page 3 and 4: 1. Introduction Many thousands of u
Page 5 and 6: language (i.e. BASIC, C, PASCAL, ..
Page 7 and 8: NAME START END DESCRIPTION LOWCORE
Page 9: ackup utility provides exceptional
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
Page 59 and 60: travels the turnpike. In this manne
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The @FSPEC SVC will transfer the fi
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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
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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
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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
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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
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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
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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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