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-DISKBUG- Diskette Debugger for CP/M 8" Single Density Disks Page 1 Note that you may do anything you want with this program except sell it. Give it away to anyone who wants it, and drop me a message with any bugs, suggestions etc. at the NECS CBBS or thereabouts. By Tom Jennings 221 W. Springfield St. Boston MA 02118 DISKBUG is a CP/M 1.4, 2.0, 2.2 or PDOS 1.17-up utility that provides read/write access to any sector or sectors of an IBM 3741 format diskette. See a later section for use with other formats. DISKBUG was originally a hack for installing a bootable CP/M system to a diskette, but has grown somewhat, so have patience with the poor command structure. There are three logical entities in DISKBUG: the sector oriented commands, the file oriented commands, and the buffer. BUFFER: All data is transferred through the buffer, whether to/from sectors or files. Data can be moved from one or more sectors to a normal CP/M disk file, or vice versa. Data in the buffer can be displayed or modified manually, similar to DDT. SECTOR COMMANDS: The sector oriented commands are all done via direct BIOS calls in CP/M, or by system calls under PDOS. One or more sectors can be read at a time, and multiple reads or writes can extend over a track boundary; for example, you can read two sequential sectors, starting at the last sector in a track. See the end of this manual for tips on using DISKBUG on other diskette formats. FILE COMMANDS: DISKBUG has a two file oriented commands. These read a disk file into the buffer, or write the buffer to a CP/M disk file. Under PDOS, the full filename spec can be used (i.e. FILE.NAME[99] ) Character case conversion is done automatically. 1 -DISKBUG- Diskette Debugger for CP/M 8" Single Density Disks Page 2 DISKBUG OPERATION DISKBUG is just a CP/M utility, run in the normal manner. It uses only 8080 opcodes, so will run on anything. (Well, anything we care about. Shows my narrow CPM-8080-Z80 point of view) It is not particularly fast, but who cares anyways. It does not use any command line arguments. All commands are quit low level, which I found appropriate for my uses, such as system installation, un- erasing files, copying files from Intel ISIS and PDP-11 diskettes. One note on the buffer. It is assumed you have a fairly large memory, like 48K or so. The buffer is fixed at 32K in length, and almost no commands do any checking on reaching the end of it, so it is possible to destroy your system memory if you try. In practice, I have had no problems. Buffer management is minimal. All commands (except display buffer and change buffer) operate from the bottom of the buffer up. The command prompt always displays the number of (decimal) bytes in the buffer. All number typed to DISKBUG are in hex. See the end of the manual for some examples. A hopefully complete description of the command set follows, with a list of features, bugs and side effects. 2 -DISKBUG- Diskette Debugger for CP/M 8" Single Density Disks Page 3 DISKBUG COMMAND SET X Select the disk to use, R Read sectors into the buffer, W Write the buffer to sectors, G Get a CP/M disk file, P Put the buffer to a CP/M disk file, D Display buffer contents, C Change buffer contents, Q Quit back to CP/M. X -Select a disk drive. This command must be performed before any sector command will operate. The disk selected will be used for all upcoming R or W commands. Note that this is independent of the disk used by the G and P commands; see those descriptions for details. R -Read one or more sectors to the buffer. You are prompted for the starting track and sector, and number of sectors. All values are in hex. Sectors are read sequentially (assuming a standard diskette) into the buffer, starting at the bottom of the buffer. Note that you cannot append to data already in the buffer; it gets overwritten. (If you need to, you'll have to P it out to a diskfile, and append it later manually.) Note that no checking is done on the amount of data read; if you specify more than 128 sectors, you will probably bash something. W -Write buffer data out to one or more sectors. As in the R command, you are prompted for the starting track and sector, and number of sectors. To be safe, it asks "Write to disk <x>:?" before actually writing, therefore allowing you to abort. Only the specified number of sectors is written, regardless of how much data is in the buffer. (even none!) G -Get a diskfile, put it in the buffer. This reads the specified disk file and puts it into the buffer, starting at the bottom of the buffer. The entire file is read until end of file. Note that you can (and probably should!) specify a disk other than the one selected by the X command. File names are specified as per normal operating system specs: X:FILE.NAM, or with the user number if PDOS. All characters are converted to upper case. 3 -DISKBUG- Diskette Debugger for CP/M 8" Single Density Disks Page 4 P -Put the buffer contents to a diskfile. All data within the buffer is written to the disk. NEVER 'P' to the same disk as selected by the X command, unless you were merely reading from it. Filenames are full legal names, as described above. The number of bytes written out is the same as listed at the prompt. D -Display buffer contents. D prompts you for a buffer starting address, and displays 256 bytes in hex and ASCII. This address is the offset from the start of the buffer, and runs from 0 to 7f00. Unfortunately, you have to maintain the buffer address/sector numbers yourself. For example, if you have read 4 sectors from track 0 sector 10, sector 10 is in the buffer at 0 to 7f, sector 11 at 80 to ff, etc. You may type CR only at the address prompt to display the next sequential 256 bytes instead of the next address. C -Change buffer contents. This command is patterned after Digital Research's DDT 'S' command. After entering the address, the current contents are displayed, and you can enter new ones. Type an illegal hex number to quit. CAUTION: Unlike DDT's 'S', typing CR only as new contents will wreck the current contents, not leave it. You MUST retype the same value if you want to leave it alone. Q -Quit back to the operating system. Pretty much self explanatory. Does absolutely nothing to the X'd disk, the buffer, or any diskfiles. 4 -DISKBUG- Diskette Debugger for CP/M 8" Single Density Disks Page 5 NOTE ON OPERATING ON OTHER TYPE DISKETTE FORMATS Although DISKBUG is meant for use only on standard eight inch single density disks, you can use it on any type diskette if you DO NOT attempt to perform multiple sector I/O the would make DISKBUG think it should change tracks, and make certain concessions. Track size is currently hard coded to 26 sectors per track. (Someday I'll finish DISKBUG so it reads the CP/M disk descriptor block...) When a sector write is done, a "write allocated" type write is done. If you write to a diskette that has physical sectors larger than 128 bytes, before you remove the diskette make sure you perform some operation that will ensure the sector actually gets written; reading a sector will do. EXAMPLES Here are some simple examples to show various things. READ THE CP/M SYSTEM TRACKS, DUMP TO A DISK FILE This is one of the simplest things to do. Select the disk to read, say A:, using the X command. Do an 'R' command, and read the first two tracks to the buffer. At this point, you might poke around with the 'D' command to see what's there. To write it to a diskfile, say, TRACK2.BIN, so you can look at it with DDT or something, use the 'P' command. In this case, you can 'P' it to disk A:, since you only read it. (0 bytes in buffer) pick one: X Disk: A (0 bytes in buffer) pick one: R Track: 2 Sector: 1 # sectors: 1A Disk IO complete (3322 bytes in buffer) pick one: D Starting address: 0 0000: 31 80 00 44 1a 7c 55 66 77 88 aa 55 4f 3e 1a 3c 1__D_|Ufw__UO>_< 0010: 41 42 43 44 45 31 32 33 34 35 61 62 63 64 65 66 ABCDE12345abcdef .... etc (3322 bytes in buffer) pick one: P File to write to: A:TRACK2.BIN (3322 bytes in buffer) pick one: Q A> 5 -DISKBUG- Diskette Debugger for CP/M 8" Single Density Disks Page 6 WRITING A DISKFILE OUT TO THE SYSTEM TRACKS This was the original use of DISKBUG. Read the diskfile, say SYSTEM.COM, to tracks 0 and 1. Note that in this example the disk file is larger than the size of the two tracks, like you SAVEd too many blocks. However, only the desired 6144 bytes will be written out. (0 bytes in buffer) pick one: G File to read: A:SYSTEM.COM Buffer contains 8192 bytes (I should delete this msg...) (8192 bytes in buffer) pick one: X Disk: B (8192 bytes in buffer) pick one: W Track: 0 Sector: 1 # sectors 33 (did I add right?) Write to disk A:? Y Disk IO complete (8192 bytes in buffer) pick one: UNDELETE A CP/M DISKFILE First, read track 2 into the buffer (r,2,1,1a) Use the 'D' command to look for the directory entry (below). Once found, use the 'C' command to change the ET byte from E5 to the desired user number (0 will do) If the file was over 16K bytes, don't forget the other extents (same filename, EX byte 1,2,3... for each extent) In order to update the disk directory, write the entire track back (w,2,1,1a) 6 -DISKBUG- Diskette Debugger for CP/M 8" Single Density Disks Page 7 BUGS AND "FEATURES" This first one is not a bug, but an undesired side effect of fiddling with the BIOS without the BDOS knowing it. Bad things can happen when you change the default disk, and you aren't careful to specify the disk when using the 'P' or 'G' commands. There is possibly a bug in the disk select stuff, however. I couldn't get it to repeat, but I thought I should mention it anyways. After performing sector reads or writes to a disk, a file access, such as 'G' or 'P' may look on the wrong disk. Fortunately, this happened only with the 'G' command ("Can't find FILE.NAM") and was not destructive. I really should add a DISK SELECT command via a BDOS call. The number and filename parsers aren't too smart. They will not report errors such as illegal hex numbers, or blank filenames. Be careful here. If you read a file greater than 32K bytes, you will probably munch something. In the 'C' command, typing CR in response to the prompt for a new value will not leave that location alone, but will change it to some random value. If you write an empty buffer to a diskfile, it will create a file with one (garbage) byte in it. ---- End of Manual ---- 7