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Text File | 1989-06-18 | 17.2 KB | 418 lines

HILOAD An utility for loading TSR's someplace else by Larry Shannon 18 Jun 1989 HILOAD is a utility program designed to load your normal TSR (Terminate-and-Stay-Resident) programs somewhere else in memory. Usually this is a place outside the normal DOS region; that is, outside the first 640K of system memory. At this time, it does not include either extended or expanded memory. BACKGROUND The 8088 used in the PC-XT is capable of addressing up to 1024K of memory. The designers of the PC and DOS decided that only the first 640K would be used by the operating system, DOS, and the rest was reserved for other uses. Because of the way the 8088 forms addresses, it is customary to refer to addresses by a segment:offset combination. The 'actual' final address is formed by multiplying the segment value by 16 (i.e., shifting it left 4 places) and adding the result to the offset address. Thus, the very first address in the machine is called 0000:0000. An address 1024 bytes from this start (hex 400) may be variously indentified as 0000:0400, 0040:0000, 0020:0200, 0038:0080, etc. For convenience, we may speak of the various segments as: 0000:0000 to 0000:FFFF Block 0 1000:0000 to 1000:FFFF Block 1 and so on E000:0000 to E000:FFFF Block E F000:0000 to F000:FFFF Block F It is easy to see that there are 16 contiguous segments of 64K each, yielding (16 X 64 =) 1024K, or one megabyte, and that DOS can only use the first 10 segments, or blocks 0 through 9. What is in the other 6 segments? Is that 384K of potential memory just sitting there idle? WHO'S USING WHAT? Well, actually not. Some of these blocks have been set aside, and are probably being used, for specific purposes. Block F is where the ROM BIOS lives and, if you have a true- blue IBM PC, where the ROM BASIC lives. So the F block is pretty well spoken for. Block B is where the memory for the video sits. If you have a Monochrome Display Adapter (MDA), it uses 4K of memory at addresses B000:0000 to B000:1000, and the remainder of the B block, 60K, is unused. In fact, if you have a straight monochrome card like IBM supplies, that's all the memory you have available. If you have a Color Graphics Adapter (CGA), it occupies memory from B800:0000 to B800:7FFF (or equivalently B000:8000 to B000:FFFF). Like the MDA, when the CGA is in text mode it only uses the first 4K of this memory, but it can support up to 8 'pages' of 4K each; when in graphics mode, all 32K are in use. Like the MDA, true-blue CGA cards, and most clone CGA cards, have only that 32K available. Enhanced Graphics Adapters (EGA) are even bigger consumers of memory, at maximum using the A block and part of the C block! If you have a hard disk, its BIOS is normally located on the hard disk controller card, and is ususlly resident at C000:8000, or as it is commonly referred to, C800:0000. SO WHAT? Astute observers will notice that the D and E blocks were pretty much left out of the above description. It is believed that these areas of memory were set aside by IBM for program cartridges, but few, if any, of these were actually produced, and this area is normally wide open and available for use. If you are like most PC users, you have only a monochrome or CGA display, and the A block is available to you also. DOWN TO BUSINESS The '640K barrier' people talk about is caused by two reasons: programs are getting more sophisticated and user-friendly, meaning they take up more memory. Secondly, there has been a proliferation of many handy programs that reside in memory (TSR's) which 'pop up' with useful information at the touch of a key or perform some other action. Examples are SideKick from Borland International, various printer buffers which are almost a necessity, and so on. It is not too unusual to have half one's DOS memory taken up with various TSR's. While there's little we can do about fat programs, we can move these TSR's out of the way. This was the driving force behind the development of HILOAD. WHERE DO I GET THIS MEMORY? Some PC clone makers map their memory into the D and E blocks; Kaypro for one does, others may also. Constructing a board to fill in these holes is not difficult, especially if static RAMS (SRAM) are used; these are now available in 32K X 8 sizes at attractive prices. An old trick is to use commercial memory cards (now obsolete but available) that allow themselves to be mapped into the desired regions. Finally, users of Hercules Graphics cards and their clones usually have the full 64K in the B block available, but only 4K is used in text mode. That 60K looks mighty attractive, as does the 'spare' memory on a CGA card...BUT...because one may easily forget there are programs in that space, switching to Herc graphics, or simulating a CGA, or using a CGA in graphics mode will really screw up the works, so this technique is not recommended. It may be used to test out the program, though, and see if it's worth the small trouble to get memory for the 'safe' areas. HOW THE PROGRAM WORKS HILOAD grabs the program you want, as well as any command tail required, and loads it into the memory area you specify. After loading the candidate TSR program, it revectors several DOS interrupts and then executes the TSR program in the new location. When the TSR program attempts to 'go resident', HILOAD traps that request, either from INT 27H or function 31H of INT 21H, resets the appropriate interrupt vectors, examines the interrupt vector table to see which ones point to the new program, and then terminates normally. Thus, when HILOAD exits, zero DOS memory is used up, and the TSR is snugly nestled in another part of memory, acting just like it normally does. HOW TO SPECIFY VARIOUS THINGS HILOAD requires various pieces of information to operate properly. Addresses - HILOAD requires a starting address for placing TSR's. After it places the first one, it keeps track of where it should place the next one by using the Intra-application Communication Area (ICA) at 0040:00F0 through 0040:00FF. It checks this area and computes an address from the information there, so the initial starting address has to be specified only once (until you change blocks). As long as the loading area is contiguous, the starting address need not be re-specified. The starting address is specified by an en- vironment variable, which is discussed be- low. Program names - The program name to be loaded must be specified with the full path name. Sorry about this, but it wasn't worth the effort to program the logic to chase down the paths to find the programs. This is not consid- dered (by me, anyhow) to be a serious ob- jection, as the typical use of this program is in your AUTOEXEC file where it is only typed in once. Starting off - Executing HILOAD without any program specified causes it to zero out the ICA. This is the easiest way to begin a loading sequence after changing the start address. SPECIFYING A START ADDRESS (ENVIRONMENT VARIABLES) When DOS loads a program, it also provides that program with a copy of what it calls the Environment. To see what the contents of your environment are, do the following: At the DOS prompt (e.g., C:\>), type SET <CR> The response will be a list of things, starting with COMSPEC and continuing with your PATH and PROMPT values (if you have any). After these values, you may or may not have additional entries. If you do, they will be of the form: name=value To add a value to the environment, type: set abc=ABCabc <CR> and then type set <CR> Notice that a new environment variable has been added. Notice also that the name, abc, has been capitalized as ABC, but the value remains as it was typed in, i.e., ABCabc. To change an environment value, type set name=NewValue<CR> and NewValue will replace the old value. To delete an environment variable, type set name=<CR> and the value will disappear from the environment. HILOAD requires an environment variable with a name the same as the program name. The value is the hex starting address. So, if the program is named HILOAD, as it is on this disk, and the desired starting value is A000, then you would set the environment variable by typing: set hiload=A000<CR> This can also be done as an entry in your AUTOEXEC.BAT file. DOS is poorly documented, but it provides the name of the program it loads, and where it came from, right after the environment. I have used this quirk of DOS to determine the name of the environment variable. If you change the program name to, say, SHIFTSR.COM, then you would set the environment variable as: set shiftsr=A000<CR> This feature (?) allows you to have multiple copies of the program under different names, each with its own environment variable, if you should so desire. NOTE: As far as I can tell, this feature is only available in DOS 3.X. The program determines the DOS version in use and, if less than 3.0, it uses a default program name of HILOAD. This is what the name of the environment variable would have to be, no matter what you rename the program to. INITIALIZING THE PROCESS As stated above, the program must first initialize the ICA. It does this by being invoked with no parameters. The 'standard' starting sequence is therefore: SET HILOAD=A000 HILOAD etc. SPECIFYING PROGRAMS TO LOAD Also as stated above, full path names must be given. Suppose you have four TSR's you wish to load, as follows: NAME SIZE PARAMETERS (TSR command tail) TSR1 14K none TSR2 22K /X /U /M=22 TSR3 1.4K none TSR4 26K 'text string' Adding them up, we see that they will occupy less than 64K, so they can all be loaded in one block. Suppose also we have the A block available for use. The series of commands in the AUTOEXEC file to perform the desired action might be: SET HILOAD=A000 starting address HILOAD initialize HILOAD \DOS\TSR1 load first tsr HILOAD \SUB1\SUB2\TSR2 /X /U /M=22 load next tsr HILOAD \TSR3 load next tsr HILOAD \UTILITY\TSR4 'text string' load last tsr The directories shown are the complete path names to the various TSR's. Suppose now you have another TSR you want loaded, but it's too big to fit in the A block; you have memory available in D block. You would follow the above sequence with: SET HILOAD=D000 reset start address HILOAD re-initialize HILOAD \SUB3\SUB4\TSR5 load it PROGRAM OUTPUT HILOAD issues various progress and error messages as it chugs along. It tells you the starting address it uses, the name of the program it is loading, what it found for a command tail to the TSR, and the amount of memory the TSR has reserved for itself. It also lists the interrupts the TSR has captured, along with their new addresses. This can be handy for debugging purposes or just finding out who captures what. Many TSRs do not go through Int 21H functions 35H and 25H to get and set the interrupt vectors; they directly manipulate the DOS interrupt table at the bottom of memory. This is not a recommended technique but many do so. HILOAD will capture these villians (SideKick being the most prominent one) and show what they trap. Incidentally, it appears that SideKick traps interrupt 21H for itself, and any TSR loaded after it, who attempts to grab Int 9H, is pushed down the list by SideKick so he (SideKick) still has first grab at the keyboard. Very clever programming; a pain in the kazoo when you're groping around to figure out what's actually happening! The above comments are based on an older version of SideKick (1.56) which I have been using. Later versions may act in a more civilized manner. KEEPING THE OUTPUT Since the information from HILOAD can whiz off the screen before you have a chance to read it, it is a good idea to redirect the output to a file instead of the screen. The program output can then be perused at your leisure. The following sequence is an example of how to do this: DEL TSRLIST.LST delete old file SET HILOAD=A000 set start address HILOAD >>TSRLST.LST initialize HILOAD \TSR1 >>TSRLST.LST load first tsr HILOAD \SUB1\TSR2 /X /Z >>TSRLST.LST load next tsr SET HILOAD=D000 reset start address HILOAD >>TSRLST.LST initialize HILOAD \UTILITY\BIGTSR /PARMS >>TSRLST.LST load big tsr After everything is loaded, the file TSRLST.LST may be browsed to see what went on, get addresses, check vectors, etc. Of course, the output may also be redirected to the printer by putting a >PRN instead of >>filename.ext ERROR MESSAGES If something doesn't go right, the program tries to tell you and exit safely. The error messages are: No address given ... ABORTING Something's wrong with the environment variable. Check spelling of variable name and make sure it agrees with the program name. The value given must be 4 hex digits, upper or lower case. Can't find file PROGNAME ... ABORTING HILOAD was unable to locate the specified program. Check to see that the path is correct. Also, only .COM files can be loaded this way; .EXE files will bomb! Requires DOS 2.0 ... ABORTING Program requires DOS version 2.0 or above. The program also issues a message when it initializes the ICA. DISCLAIMER TSRs are tricky things; SideKick is notorious for being sensitive to the order in which other TSR's are loaded. Experiment with loading your TSRs in the 'normal' fashion until you get a loading sequence that works. Use that order to HILOAD them and all should be well. LEGAL STUFF This program is being placed in the public domain. It may be copied and distributed freely for non-commercial uses. Both this file and the executable code must be distributed together and unmodified. Any brand names mentioned are copyright by their respective owners. SHEEPISH ADMISSION This program was developed over a period of time as I was learning about TSRs and revectoring interrupts, etc. Also, though the objective of the program remained firm, the little niggly details kept changing on me as I thought of alternate ways to accomplish things and more frills were added. Consequently, the source code is comprehensible to me but I'm sure looks like a real mess to the 'seasoned professional'. I am thus a little ashamed to release it for public scrutiny and scorn. However, it is included and commented as best as I can recall what each little piece does. Don't bother to tell me there are 'dead code' areas and unused variables. Anybody who wants can modify it to their hearts' content, but please take note of the distributon restriction noted above. Larry Shannon 5615 Truscott Terrace Lakeview, NY 14085 - end -