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

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identify the correct Data Address Mark. Directory sector writes should be verified with the @VRSEC SuperVisor Call. Expect to obtain an error code 6 as previously noted. 5.2 THE GRANULE ALLOCATION TABLE (GAT) The Granule Allocation Table (GAT) contains a section of information pertinent to the allocation of physical storage space on the disk. For floppy disk drives, this section is composed of two tables: The ALLOCATION table specifies what areas of the disk are allocated or unavailable for use while the LOCKOUT table specifies what areas of the disk are physically unusable. For winchester drives (hard drives), the LOCKOUT table is not used and the ALLOCATION table is extended to include the GAT space normally used by the floppy lockout table. The GAT is wholly contained in the first sector of the directory cylinder. Additional fields are stored within the GAT sector that describe the disk (its pack identification). The GAT also contains certain data specific to the formatting configuration of the disk. An entire disk is divided into cylinders (tracks) and sectors. The standard sector size is 256 bytes in length. Each cylinder has a specified constant quantity of sectors. Because the DOS uses a single 8-bit register to communicate sector numbers, it will support a maximum of 256 sectors per cylinder. A group of sectors is allocated whenever additional space is needed. This group is termed a GRANULE and is always a constant size for any given disk. This does not mean that the granule is the same size for all disks. The size of a granule generally increases with the increasing size of the disk storage device. The choice of a granule size is a compromise over minimum file lengths and overhead during the dynamic allocation process. It is somewhat dependent on the number of sectors per cylinder because the number of sectors per granule must divide evenly into the number of sectors per cylinder. The ALLOCATION and LOCKOUT tables are actually bit maps that associate one granule of space per bit. One byte is used to store the information on a single cylinder; therefore, the GAT is configured to provide for a maximum of eight granules per cylinder. In these tables, each bit that is set indicates a corresponding granule in use (or locked out). A reset bit indicates a granule free to be used. In the GAT allocation and lockout bytes, bit 0 corresponds to the first relative granule on a cylinder (denoted as granule 0). Bit 1 corresponds to the second relative granule (denoted as granule 1), bit 2 the third (denoted as granule 2), and so on through bit 7 for the eighth granule (denoted as granule 7). This is illustrated in figure 5-1. ============================================================= | ______________________________________________________ | | |7|6|5|4|3|2|1|0||7|6|5|4|3|2|1|0||7|6|5|4|3|2|1|0||... | | | cylinder 0 || cylinder 1 || cylinder 2 ||... | | |1 1 1 1 1 0 0 1||1 1 1 1 1 0 0 0||1 1 1 1 1 0 0 0||... | | |_______________||_______________||_______________||___ | | | ============================================================= Figure 5-1: Allocation Table Representation A 5-1/4" single density diskette is formatted at ten sectors per track, five sectors per granule, two granules per track. A two-sided diskette has twice the number of granules per track available on each cylinder. Thus, the single density single, sided 5-1/4" configuration will use only bits 0 and 1 of each GAT byte. The remaining GAT byte will contain all 1's - thereby denoting unavailable granules. A 5-1/4" double density diskette is formatted at 18 sectors per track, six sectors per granule, three granules per track. Thus, this configuration will use bits 0, 1, and 2 of each GAT byte. The standard granule allocation conventions used by the DOS for floppy diskettes are as shown in figure 5-2. 5-2
============================================================== | | | SECTORS PER SECTORS PER GRANULES PER MAXIMUM | | TRACK GRANULE TRACK CYLINDERS | | ----------- ----------- ------------ --------- | | 5" SDEN 10 5 2 96 | | 5" DDEN 18 6 3 96 | | 8" SDEN 16 8 2 77 | | 8" DDEN 30 10 3 77 | | | ============================================================== Figure 5-2: Allocation for Single-Sided Floppy Media Figure 5-2 assumes single sided media. The DOS supports two-sided operation within the confines of the hardware interfacing the physical drives to the CPU. A two-headed floppy drive functions as a single volume with the second side treated as an extension of the first in a true cylinder structure. A bit in the Drive Control Table (DCT) indicates onesided or two-sided drive configuration. A winchester-type hard disk also has a similar configuration. However, since many different sizes of winchesters are available, the recommended configurations for representative hard drives are covered in chapter 6 - DISK FILE ACCESS AND CONTROL. For the purposes of this chapter, it is sufficient to mention that hard drives may use the first 203 GAT bytes to reference ALLOCATION information (positions X'00' through X'CA'). Hard drives that exceed 203 physical cylinders require remapping or partitioning. Methods of achieving remapping and partitioning are also discussed in chapter 6. The following describes the structure of the Granule Allocation Table and the information contained in it. The numbers in angle brackets indicate the relative positions of the field within the GAT. Figure 5-3 illustrates the entire GAT. 5.2.1 ALLOCATION TABLE - This table contains a bit image of what space is available for use (and conversely what space is not available). GAT+0 corresponds to cylinder 0, GAT+1 corresponds to cylinder 1, GAT+2 corresponds to cylinder 2, and so forth. As previously noted, bit 0 of each byte corresponds to the first granule on the cylinder, bit 1 corresponds to the second granule, etc. A "1" indicates the granule is not available for use. The amount of GAT space assigned to this table permits a maximum of 96 cylinders; however, the formatter restricts the format of 8" media to 77 cylinders. 5.2.2 LOCKOUT TABLE - This table contains a bit image of what space has been locked out from use. Granules may be locked out because they either do not physically exist (i.e. granules 3-7 on 5-1/4" double density floppy media) or the verify process of the floppy formatter had detected a bad sector in a granule. The table corresponds on a cylinder for cylinder basis as does the allocation table. It is used specifically during mirror-image backup functions to determine if the disk has the available capacity to effect a backup of the source diskette. 5.2.3 EXTENDED ALLOCATION TABLE - This table is used in hard drive configurations by extending the ALLOCATION table from X'00' through X'CA' and omitting a distinct lockout table. The table then provides a capacity of up to 203 cylinders. The hard drive DBLBIT bit is available in the Drive Control Table to permit combining two physical cylinders into a single logical cylinder provided the limit of 256 sectors per cylinder is not exceeded. This arrangement therefore provides support for up to 406 cylinders. Lockout information, where available, is generally denoted by setting the appropriate bit assigned in the ALLOCATION table. 5-3
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 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: 5. The DOS Directory Structure 5.1
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
Page 93 and 94: Directory to Buffer Entry: B 1; Fun
Page 95 and 96: 7.6.31 @FLAGS$ SVC-101 This SVC wil
Page 97 and 98:
NFLAG$ This "network" flag is used
Page 99 and 100:
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
Page 111 and 112:
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
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
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Error 28: End of file encountered T
Page 133 and 134:
8.5 HEADER PROTOCOL OF MEMORY MODUL
Page 135 and 136:
This is obviously an extremely usel
Page 137 and 138:
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
Page 147 and 148:
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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