C/C++ Interactive Guide

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■──────────────────────────■ AN ADAPTABLE DISK UTILITY ■─────────────────────────── AME Computing Systems 1989 16 Leyte Drive Surrey Downs SA 5126 Australia CONTENTS ■──────────────────────────────────────────────────────────────── Page Section 1. Overview 1 1.0 Introduction 1 1.1 Operation 1 1.2 Adjusting the PC's 1 Disk Format Tables 1 1.3 Adapting the Utility 1 1.4 Determining the Disk Format 2 Section 2. Commands 8 2.1 Dump 8 2.2 Edit 8 2.3 Read a Sector 8 2.4 Write a Sector 9 2.5 Increment or Decrement 9 Sector or Track 2.6 Set/Specify Current 9 disk location 2.7 Vary disk parameter limits 10 2.8 Sector Translation and 11 Format Skew 2.9 Disk Copy 12 2.10 Modify Disk Base Table 2.11 Log Drive 12 2.12 Copy 12 2.13 Quit 12 Section 3. Examples 13 Tables: 1. Contents of the PC's DISK_BASE table 3 2. Disk status bytes 4 Listings: 1. C structure 5 2. Typical calling technique 5 3. Functions 6 AN ADAPTABLE DISK UTILITY SECTION 1. OVERVIEW 1.0 Introduction There are many reasons for wanting to read non-standard formats. These range from wishing to look at backup disks created through such programmes as PC-BACKUP, FASTBACK, to reading other computer disk formats. However, probably the most common reason is that the PC, to most people, was not their first machine. Many of us started with CP/M and Apple IIs before graduating to the PC and we had to find some way of porting that old data to the PC. If you still have the old computer, no problem, just load up a copy of MITE or PROCOMM on the PC and then with one of the many public domain CP/M communication packages, connect an RS-232 link between the computers, and that's it. Many other utilities have in-built formats and work on the premise your disk format just 'must' be supported and have no inbuilt tools to allow you to adapt the package to your format. 1.1 Operation ADU, for an Adaptable Disk Utility, will scan the disk, building up a disk parameter table. Once such a table is set up you can adjust any of the disk operating system dependencies such as system track offsets, before reading and editing. The user interface follows other utilities by providing an inbuilt full screen editor, so that patching and editing the disk is a simple task. It should be noted that this disk utility has been designed to specifically work with only floppy disk drives. Hence even though you may specify greater than 2 drives, this does not infer that the system fixed disk can be scanned. Thus, for example if drives A: and B: are 360k drives and drive C: is a fixed disk, and drive D: is a 3.5" floppy, ADU will ignore drive C:. Hence under this senario you may log drives 0,1 or 3. The reason for this is that ADU will always use INT 13H for all its disk I/O to ensure compatibility. ADU is also limited by the physical limits of the PC's Floppy Disk Controller. That is if the FDC can read 360k, 1.2M, 1.44M drives then it will function correctly provided the disk format recording method is Modified Frequency Modulation (MFM) or Standard Frequency Modulation (FM). The recording methods used by Apple (GCR) is incompatible with the PC's disk controller and cannot therefore be used to read Apple disks. The method normally used to overcome this problem is to design a device which is format insensitive and reads all the disk data irrespective of gaps and format fields etc. Software is then used to re-construct the data. 1.2 Adjusting the PC's Disk Format Tables The standard PC diskette format is made up of 40 tracks, each containing 9 sectors of 512 bytes/sector. Vary this in any way and the PC chokes. The PC will make a great deal of noise recalibrating and retrying but in vain, a point not lost on software vendors who protect their product through this form of copy protection. For an interesting article on how to achieve a limited level of copy protection see Micro Systems/Journal, July/August 1986. The first step in achieving a more flexible and unconstrained disk utility was to tell the PC's FDC to adapt to a non-PCDOS type disk format. It is the IBM PC's BIOS with its inbuilt flexibility in allowing many of its functions to be table driven that solves the problem. For instance, each time the BIOS is called to perform a disk function through INT 13H, it calls BIOS routine GET_PARM which indexes into a table called DISK_BASE. DISK_BASE is a collection of FDC parameters which tells the BIOS in what manner the FDC chip must be programmed to correctly read the diskette. Table 2 explains the variables and a partial listing from the disk utility ADU is included as listings 1 to 3 in order to demonstrate how to vary the DISK_BASE pointer from within a high level language. 1.3 Adapting the Utility Some of the parameters relating to the GAP lengths must be determined empirically and are of most concern during attempts to read multiple sectors during a diskcopy or formatting process. This is due to the fact that these GAPs are basically buffers designed to allow the controller's data separator the option of 'turning off' during splices or periods of unknown data. If the Phase Locked Loop (PLL) within the data separator was not instructed to turn off, it may get out of synchronisation and thereby not be able to lock onto the identification (ID) marks. An incorrect GAP setting can thus 'turn off' the data separator during an area of good data. Errors of this type normally manifest themselves as 'Time out errors' (BIOS return code 80H). The BIOS's diskette status area is maintained at address 0040:0041. The diskette status data map is shown in Table 2. 1.4 Determining the Disk Format ADU determines the disk format by first replacing the current generic disk vector with an alternate set as shown in Listing 2. Once this vector is in place, ADU calls the BIOS by using INT 13H. The call to the BIOS's disk I/O routine is done with a generic set of parameters. Thus, if the BIOS does not return an error then the set of parameters chosen is correct for the particular disk. If, on the otherhand, the BIOS does return an error then the parameter you are trying to determine is adjusted. For example, the bytes/sector code would be continually varied from 00 to 05 on, say, track 0, sector 1 until a nil error is returned. This obviously represents the bytes/sector. Once the number of bytes/sector is determined, it is a small matter to begin a sector 1 looking for the total number of sectors by incrementing the sector number performing a seek/verify until an error occurs. This error would then represent the sector limit. Next, look for a match on side 1 to determine the number of sides. We're almost there: all we need to know now is the number of tracks, set an upper limit and begin stepping out. The number of sectors per block are user definable, as are all the other parameters, but defaults to 8 sectors per block. The number of sectors/block is only important during the copying of CP/M type disks. As with other parameters, the block size is able to be varied so if you don't want to work in blocks then just set sectors/block to one. DB 11001111B ;SRT=C, HD UNLOAD=F DB 2 ;HEAD LOAD=1,MODE=DMA DB 37 ;WAIT AFTER OPERATION UNTIL ;MOTOR TURNS OFF DB 2 ;CODE FOR 512 BYTES/SECTOR ;1=256,2=512,3=1024 ETC DB 9 ;LAST SECTOR ON TRACK DB 2AH ;GPL IS GAP3 LENGTH FOR DATA ;READ AND DETERMINES HOW LONG ;VCO WILL 'IDLE'. MUST BE ;ADJUSTED. DB 0FFH ;DATA LENGTH, LEAVE AT 0FFH DB 50H ;GAP3 LENGTH FOR FORMAT COMMAND ;MUST BE ADJUSTED FOR SOME ;DISK FORMATS. DB 0F6H ;FORMAT FILLER BYTE. CAN BE ;ALTERED IF REQUIRED. DB 25 ;HEAD SETTLING TIME (MILLI SECONDS) DB 4 ;MOTOR START TIME (1/8 SECONDS) Table 1: Contents of the PC's DISK_BASE table. Note: The set of parameters contained in DISK_BASE are used by the BIOS for normal diskette operations. This paramater block is pointed to by the BIOS variable DISK_POINTER located at 0000:0078, which is equivalent to the address of interrupt 1EH. This pointer value can be redirected to point to a new set of parameters thus allowing the PC to access non DOS type formats. SEGMENT 0040:OFFSET OFFSET LABEL DESCRIPTION 003E SEEK_STATUS DRIVE RECALIBRATION STATUS BITS 3-0 = DRIVE 3-0. DRIVE NEEDS RECAL IF BIT = 0 003F MOTOR_STATUS MOTOR STATUS BIT 3-0 = DRIVE 3-0 AND INDICATES DRIVE IS CURRENTLY RUNNING 0040 MOTOR_WAIT COUNTER BEFORE DRIVE TIME OUT. JAMMING A LOWER VALUE THAN 37 WILL REDUCE THE NORMAL WAIT TIME. 0041 DISKETTE_STATUS BIOS RETURNS STATUS BYTE HERE TIME_OUT 80H BAD_SEEK 40H BAD_CONTROLLER 20H BAD_CRC 10H DMA_BOUNDARY 09H BAD_DMA 08H SECTOR_NOT_FND 04H WRITE_PROTECT 03H BAD_ADDR_MARK 02H BAD_CMD 01H 0042 CONTROLLER_STAT AN AREA OF 7 BYTES IS RESERVED FOR BIOS TO FILL WITH THE CONTROLLER STATUS BYTES. SEE THE I8272 DATA SHEET FOR THE VALUES RETURNED. Table 2: Disk Status Bytes. Note: The PC's BIOS maintains a set of status bytes in the PC's low memory area. Data segment 0040 is used to store these and other variables. The hardware disk analyser makes use of these bytes. ■─────────────────────────────────────────────────────────── ──────────■ Listing 1. C structure to define the parameters contained in the PC BIOS's DISK_BASE. typedef struct { unsigned char srt; /* Step rate */ unsigned char hld; /* Head load time */ unsigned char motor_wait; /* Motor Wait time */ unsigned char bytes_sect; /* Bytes/Sector code */ unsigned char eot; /* Last sector */ unsigned char rw_gap; /* Gap 3 */ unsigned char dtl; /* Data length norm 0xff */ unsigned char format_gap; /* Gap used in format */ unsigned char format_fill; /* Format fill (f6h) */ unsigned char hs; /* Head step period */ unsigned char motor_start; /* Motor start time */ } disk_base; /* disk_base template */ /* Declarations to user disk_base. */ disk_base alien_base, dos_base; /* disk base structures */ disk_base far *pc_disk_vector; /* pointers to both the */ disk_base far *alien_disk_vector; /* standard and alien */ /* disk bases */ ■─────────────────────────────────────────────────────────── ─────────── ■─────────────────────────────────────────────────────────── ──────────────■ Listing 2. Typical calling technique to routines which setup alien disk_base by filling disk_base with alternate parameters, and then altering the disk_parameter pointer to point to the new DISK_BASE. (See listing 3) pc_disk_vector = get_disk_vector(); /* save standard table */ set_alien_parms(); /* fill the alien */ /* disk_base with some */ /* initial values */ set_disk_vector(alien_disk_vector); /* replace standard table */ /* with alien table */ ■─────────────────────────────────────────────────────────── ─────────■ ■─────────────────────────────────────────────────────────── ─────────── Listing 3. Functions which are called by both ADU.C and DE.C to modify the disk_base parameters and to manipulate the disk_parameter pointer to point to the modified disk_base. See listing 2 for method of interfacing. /* Get the current disk vector by asking DOS to fetch the interrupt vector from 0x1E. The pointer is returned, and is saved by the calling module. */ disk_base far *get_disk_vector() { struct SREGS segregs; disk_base far *longptr; unsigned long ls,lo; inregs.h.ah = 0x35; /* DOS function number */ inregs.h.al = 0x1E; /* Disk vector number */ intdosx (&inregs,&outregs,&segregs); ls = (unsigned long)(segregs.es << 16); lo = (unsigned long)outregs.x.bx; longptr = (disk_base far *)(ls | lo); /* convert to the */ /* correct type */ return (longptr); } /* Replace current disk vector with the value pointed to by vectptr. This routine is normally used to swap between the Alien and PC disk vectors. */ set_disk_vector(vectptr) disk_base far *vectptr; { struct SREGS segregs; inregs.h.ah = 0x25; inregs.h.al = 0x1E; inregs.x.dx = FP_OFF(vectptr); segregs.ds = FP_SEG(vectptr); intdosx (&inregs,&outregs,&segregs); return outregs.x.ax; } /* Initialise all default variable settings. Used during initial programme activation and during logs. */ set_alien_parms() { /* Standard DOS format */ dos_base.srt = 0xcf; dos_base.hld = 2; dos_base.motor_wait = 25; dos_base.bytes_sect = 2; dos_base.eot = 8; dos_base.rw_gap = 0x2a; dos_base.dtl = 0xff; dos_base.format_gap = 0x50; dos_base.format_fill = 0xf6; dos_base.hs = 25; dos_base.motor_start = 4; /* Basic ALIEN disk data. Most parameters are modified on the fly during the disk identification process. */ alien_base.srt = 0xcf; alien_base.hld = 2; alien_base.motor_wait = 0x25; alien_base.dtl = 0xff; alien_base.format_fill = 0xf6; alien_base.hs = 25; alien_base.motor_start = 4; /* Gap tables can be obtained from 8272 data sheet */ if (alien_base.eot <= 9) { /* standard format */ alien_base.rw_gap = 0x2a; alien_base.format_gap = 0x50; } /* see 8272 data sheet */ else { /* for other formats*/ alien_base.rw_gap = 0x02; alien_base.format_gap = 0x20; } ■─────────────────────────────────────────────────────────── ─────────■ SECTION 2: COMMANDS This section describeS each command including examples of each command. Apart from the disk commands, the function keys F1, F3 and F4 provide the following utility: F1 will give you help. F3 will re-issue the command without CR. F4 will re-issue the command with CR. All commands are either single or double letter. Capital letters in the following sections indicate the number of significant letters in the command. Commands may be separated by a semicolon. For example, +S;R;E will increment the sector, read it in, then go to edit mode. 2.1 Dump Dump has no arguments and will dump the current buffer contents to the screen in both hex and ascii formats. No editing facilities are provided within Dump, as this command is normally used when searching the disk for data sequences, etc. To assist searching for particular text issue the command >>+s;r;d. Pressing F4 will interrupt the dump and increment the sector. Be aware that this command will not increment the sector past the last sector on the disk. 2.2 Edit The Edit command has no arguments, and will allow full screen editing of the current buffer's contents. The following keys on the PC are supported in this mode: Left Arrow: Move the cursor left Right Arrow: Move the cursor right Up Arrow: Move the cursor towards the top of the buffer Down Arrow: Move the cursor towards the bottom of the buffer End: Moves the cursor to the end of the buffer Home: Move the cursor to the beginning of the buffer Esc: Exits the Edit session WITHOUT saving to disk F5: Writes buffers contents to disk F6: Reads disk sector to buffer for editing etc 2.3 Read a Sector Read [T] [S] [H]: The Read command will read either the currently selected disk sector into memory, or the command line sector location. If a command line option is used the default ADU Track, Sector and Head parameters are altered to the ones selected as part of the Read command. Either decimal or hexadecimal numbers may be entered. For example: Read 0x20 9 0 will read in sector 9, side 0 of track 32 into memory. Read 21,3,1 will read in sector 3, side 1 of track 21 into memory. 2.4 Write a Sector Write [T] [S] [H]: The Write command will write the current buffer contents to the currently selected disk sector. If a command line option is used the default ADU Track, Sector and Head parameters are altered to the ones selected as part of the Write command. Either decimal or hexadecimal numbers may be entered. For example: Write 0x20 9 0 will read in sector 9, side 0 of track 32 into memory. Write 21,3,1 will read in sector 3, side 1 of track 21 into memory. 2.5 Increment or Decrement Sector or Track +S,-S This command will decrement or increment the current sector by unity. If an attempt is made to increment or decrement outside the selected sector range an error message is generated. +T,-T This command will decrement or increment the current track by unity. If an attempt is made to increment or decrement outside the selected track range an error message is generated. 2.6 Set/Specify Current disk location The set command allows a sector, track, or block to be selected without having to use either the increment or decrement command. The set command is restricted to the allowable disk parameter limits. Set Block (SB): Sb N The set block command will set the current block number to N. This has the effect of calculating the relevant track, side and sector number and setting the parameters accordingly. Set Track (ST): ST N: The set track command will set the current track number to N. Set Sector (SS): SS N: The set Sector command will set the current track number to N. Set Head (SH): SH N The set head command will set the current head number to N. 2.7 Vary disk parameter limits The Vary Parameter command allows a configuration of disk parameters to be selected which are outside of those which were detected by the disk utility as it logged the disk. This is a useful command if it is considered the disk has an un-usual formatting scheme. The vary command varies the internal ADU parameters whereas the Set command varies the current controller head position. For example: VT 41 Vary number of tracks to 41 VO 2 Vary system offset to 2 Vary Block VB N: The Vary block command will vary the number of calculated blocks on the disk. The default sectors/block is assumed to be 8. If you do not wish to work in terms of blocks (used in C/PM) you may use VB to set the sectors/block to 1. Vary Track VT N: The Vary Track command will vary the number of tracks on the disk from that which was calculated at log. For example a 40 track drive can be set to 41 in order to look at the outer tracks. Vary siZe VZ N: The Vary siZe command will vary the number of bytes per sector. For example to vary from the standard value of 512 bytes/sector, for example VZ 1024 would set the number of bytes/sector to 1024. Vary End of Track VE N: The Vary End of track command will vary the number of sectors/track on the disk. For example if a DOS disk is scanned, and ADU has determined the disk has 9 sectors/track VE 10, will allow you to look for higher numbered sectors on other tracks. Vary Heads VH N: The Vary Heads command allows the number of heads to be altered. Vary Drives VD N: This command allows the number of Drives in a system configuration to be varied from the current default which is two. That is A and B. Vary Offset VO N: The Vary Offset command allows the block offset to be varied. The block offset is normally the beginning of the data on the disk, and is a way of jumping over the system area on the disk. If this is not desirable then the VO 0 command would allow ADU to begin calculating blocks from track 0, sector 1, of side 0. Also, for example if you wished to map the disk from a the perspective of the sectors of the disk then the command VO 0; VB 1 would allow ADU to map blocks to sectors. Hence the number of blocks would be the number of sectors on the disk. This would allow you to copy every sector of the disk into a DOS file. Taking the example one step further. Assume you wished to copy the first sector of every track on side 0 to a DOS file called side0.doc, the following command sequence would be used: VO 0; VB 1; VE 1; VH 1; C C:side0.doc 0/39 2.8 Sector Translation and Format Skew Some disk systems employ interleaving through either software or hardware in order to speed the response of the disk access. This technique is essential in a matching of the CPU speed to the disk controller speed so that the minimum latency is obtained during disk accesses. ADU supports hardware skew when formatting a disk, so that if a disk needs to be copied which employs a hardware sector interleaving then it will be necessary to use the Format Skew (FS) command to vary the physical location of the sectors on the disk's track. When reading a disk which has employed software skew then it follows that the data coming off the disk will not be in sequence, hence the Sector Translation (SX) command can be used to rearrange the sequence of sectors on being read off the disk. This allows you to ensure the data being search or copied will be contiguous. Format Skew FS [n1,n2,n3.....] This command allows the Format process to work correctly when carrying out a "disk copy" of an Alien Disk. Once you have determined the skew the source disk has used, using the Sector Translate (SX) command then the FS command is used to key in the correct sector sequence, for example FS 1,3,5,7,9,2,4,6,8 programmes ADU with a sector interleaving of 2. The single command of FS will output the current skew table onto the status line. Sector Translate SX [n1,n2,n3.....] This command allows you to experiment with the Disk's sector translation in order to ensure that the data being read off the disk is contiguous. This command provides an important tool when attempting to copy files off an alien disk to a DOS file or attempting to carry out a "Disk Copy". If a text file exists on the alien disk of greater in length than one sector then it should be possible to vary the sector table until the text appears contiguous when using a command sequence such as +s;r;e. If you wish to make a disk copy of the disk then the format skew (FS) may also have to be used. The single command of SX will output the current translation table onto the status line. 2.9 Disk Copy DC The current implementation of Disk Copy assumes you will be copying from the A drive to the B drive and that furthermore both A and B drives have compatible hardware. This disk copy process will begin by reading disk A on a cylinder per cylinder basis before formatting the B disk using the current disk and format skew tables. After a successful cylinder format, diskcopy will then write the cylinder to the disk in drive B. If the Disk Copy command appears to time out, then this could be due to the controller timing out due to an incorrect Format Skew. Vary the format skew using the FS command. 2.10 Modify Disk Base Parameters DB [p1,p2,p3....] The Disk Base command allows the PC's disk base parameter Block to be modified independently of this programme's Log facility. Thus if the disk scan is not successful for any reason, then the disk parameters may be adjusted or tunned to a particular disk. The command DB without parameters will display the current contents of the table. If there is any doubt about the purpose of these values, refer either to the IBM PC Technical Reference Manual, the Intel 8272 data sheet. Table 1 gives a succinct summary of the purpose of the parameters. 2.11 Log Drive L [N] The log command allows a new disk to be analysed. If no drive is specified then the existing drive is used. The number of drives allows is variable using the Vary Drive command. The default value is always two. 2.12 Copy Command C N:fn Blocks Range This command allows a range of blocks to be copied from the alien disk to a contiguous DOS file. The block size is dependent on the user and can be set to one sector representing a block by using the command VB 1. This is a very useful command if a file resides on an obscure formatted disk. Determining the format is usually straight forward and coupled with this command allows the old file to be easily ported to the PC. If you wish to copy individual sectors, rather than the number of sectors which make up a block, then set the block size to 1 sector/block using the VB 1 command. For example to copy a file client.doc from an alien disk to a your a DOS disk in your B drive use the command: C B:client.doc 2,3,4,6/39. This command sequence copies blocks 2,3,4 and 6 to 39 inclusive from the alien disk to the B drive under the file name client.doc 2.13 Quit Command: Q The quit command restores all the PC's environment to that which existed prior to ADU being invoked and then exits ADU. SECTION 3: EXAMPLES >>C c:junk.dat 2/32 ; copies blocks 2 to 32 from alien disk ; into file junk.dat on drive C: >>R 32,2,0;E ; reads data into buffer from track 32, ; sector 2, side 0, and then enters edit mode >>W ; ...after editing W will write back to disk ; using the current Track,sector and side. >>+T;R;D ; Increment Track, read data into buffer and ; then dump to screen. As a final example, suppose you want, for some reason, to copy only sector 1 from each track on side 0 to a file on say drive C, for analysis, Then the following commands will allow you to do it: (note they could all be on one line!) >>Vb 1 ; set sectors per block to 1 >>Ve 1 ; set disk to 1 sector per track >>Vh 1 ; set disk to single sided ie one head >>Vo 0 ; set first block offset to track 0 >>C C:sects.1 0/39 ; copy blocks 0 to 39 to file sects.1 ; on drive C: >>Vz 1024 ; vary sector size, useful for looking ; at strange disks which are for example ; copy protected.