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

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NAME NUMBER FUNCTION DESCRIPTION @DCSTAT 40 0* Test disk controller status @SLCT 41 1* Select a disk drive @DCINIT 42 2 Initialize a disk controller @DCRES 43 3 Reset a disk controller @RSTOR 44 4* Restore a drive to cylinder 0 @STEPI 45 5* Issue track step-in to controller @SEEK 46 6* Seek to a disk cylinder @RSLCT 47 7* Reselect a busy drive until available @RDHDR 48 8 Read ID field @RDSEC 49 9* Read a disk sector @VRSEC 50 10* Verify the readability of a disk sector @RDTRK 51 11 Read a disk track @HDFMT 52 12* Format an entire drive @WRSEC 53 13* Write a disk sector @WRSSC 54 14* Write a disk directory sector @WRTRK 55 15* Write a disk track (format data) Figure 4-6: Disk Controller Communications Note: Functions asterisked are supported by the DOS floppy driver Before taking a look at the HDC commands versus the disk controller communications functions, let's address exactly what functions are used in the DOS. The DOS spends a great percentage of the controller's time in reading and writing. These DOS functions use @RDSEC to read disk sectors, @WRSEC and @WRSSC to write non-system and system sectors respectively. Where the application is requesting verification (or where the DOS is writing a system sector), then the @VRSEC function is used which should read the designated sector without disturbing the disk file I/O buffer. Next, the logging function uses @SEEK and @RSLCT to obtain status from the disk. FORMAT uses @WRTRK for the FDC and @HDFMT for the HDC as well as @SLCT, @RSTOR, and @STEPIN in addition to the previous SVCs. BACKUP and FORMAT also use @DCSTAT to make sure that the drive is enabled. These functions are indicated by an asterisk in figure 4-6. The four remaining functions, @DCINIT, @DCRES, @RDHDR, and @RDTRK are provided in case utility software needs these requests for communications with custom drivers [NOTE THAT THE FDC DRIVER SUPPLIED WITH THE DOS DOES NOT SUPPORT THESE FUNCTIONS]. If we look at the HDC commands, we observe that although the DOS commands provided can not uniquely request all of the commands of every controller, the DOS commands do provide the means to satisfy all of the necessary functions. In fact, some DOS functions are not even needed in the case of the HDC and hard disk system. When the operating system passes the SVC request to the disk driver The manner in which the driver controller linkage is established is by passing a function value contained in register "B" to the software driver that interfaces to the controller. Sixteen functions have been defined within the DOS. The table in figure 4-6 briefly describes these functions. At this point, it would be beneficial to discuss exactly what operations are performed by the operating system when it receives one of the Disk Controller Communications SVC requests. All of the requests use register C to reference the logical drive number. The DOS uses this value to index the Drive Control Table and obtain a pointer to the DCT record associated with the logical drive. After saving the index register, the DOS places the pointer into IY. The DOS saves register pair BC and places the function code corresponding to the function as shown in figure 4-6 into register B. The DOS will also issue an @BANK request to bring in bank zero. This operation will ensure that bank zero is resident for a disk I/O operation. It also limits the location of disk drivers or disk filters [like MONITOR 4-11
available from Logical Systems, Inc.] to reside in either the low memory driver region or in upper memory of bank zero. Upon return from the disk driver, the DOS will restore the previously resident RAM with another @BANK request. The DOS then places an "Illegal drive number" error code (32) into the accumulator, resets the Z-flag, then executes a "CALL" to a "JP (IY)" instruction. The purpose of this strange linkage becomes evident when we examine the result. The first byte of the DCT is interpreted as an RET instruction if the drive is disabled. Since register IY is pointing to that byte, the linkage will return back to the caller with the "Illegal drive number" error. If the drive is enabled, the first DCT byte is interpreted as a JUMP instruction which will transfer control to the entry point of the driver. We can now show the uniform register protocol upon entry to a disk driver. This protocol is illustrated in figure 4- 7. Register Direction Condition/Value AF => Irrelevant upon entry to the driver B => Contains the function code of the request C => Contains the logical drive number D => Contains the cylinder being requested E => Contains the relative sector being requested HL => Contains a pointer to the I/O buffer, where applicable IY => Contains a pointer to the proper Drive Control Table entry A
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 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: Command Purpose RESTORE Recalibrate
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
Page 61 and 62: The @FSPEC SVC will transfer the fi
Page 63 and 64: A high level language permits you t
Page 65 and 66: does exist, @RENAME should return e
Page 67 and 68: Next, it would be very useful if th
Page 69 and 70: LD HL,FCBX+9 ;Point to the LRL fiel
Page 71 and 72: operating system for such a purpose
Page 73 and 74: position where the last character i
Page 75 and 76: ecord. If a file has more than four
Page 77 and 78: DE Contains a pointer to the File C
Page 79 and 80: @RENAM SVC-56 Rename a file on disk
Page 81 and 82: @FNAME SVC-80 Obtain filespec given
Page 83 and 84: @WRSEC SVC-53 Write a disk sector @
Page 85 and 86: 7.6 SUPERVISOR CALL DETAILS 7.6.1 @
Page 87 and 88: Note: @EXIT in SYS1 automatically r
Page 89 and 90:
7.6.10 @CLOSE SVC-60 This SVC will
Page 91 and 92:
7.6.18 @DCSTAT SVC-40 This SVC pass
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Directory to Buffer Entry: B 1; Fun
Page 95 and 96:
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
Page 101 and 102:
7.6.40 @HEX8 SVC-98 This SVC will c
Page 103 and 104:
7.6.48 @KLTSK SVC-32 This SVC will
Page 105 and 106:
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
Page 125 and 126:
===================================
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The TYPE=0A indicates that it is th
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Error 08: Device not available A re
Page 131 and 132:
Error 28: End of file encountered T
Page 133 and 134:
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
Page 139 and 140:
8.7.3 Details of Low Memory Page 2
Page 141 and 142:
actual bank switching. As previousl
Page 143 and 144:
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
Page 149 and 150:
8.13 USING @PARAM The @PARAM SuperV
Page 151 and 152:
DW LPARM+1 DB 'FEED ' ;Line feed pa
Page 153 and 154:
;*=*=* PPARM LD BC,0 ;Zero because
Page 155 and 156:
8.14 TRAP Filter Illustrated ;TRAP/
Page 157 and 158:
8.15 SLASH0 Filter Illustrated ;SLA
Page 159 and 160:
8.16 DMP-500 BOLDFACE Filter Illust
Page 161 and 162:
NOMEM$ DB 'High memory is not avail
Page 163 and 164:
@ @ABORT..........7-2, 7-4, 7-8, 7-
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