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- Fix Catalog document per Issue #567 - Update fonts.txt w/ latest font info - Correct EOL on several documentspull/570/head
Wayne Warthen
8 months ago
17 changed files with 1222 additions and 723 deletions
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Z P M 3 by Simeon Cran |
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======================== |
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|
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A Z80 coded CP/M 3.0 compatible BDOS replacement. |
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The first public release: 27/3/92 |
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This document dated: 16/6/92 |
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Distributed at: Z-Node 62 (Perth, Western Australia) |
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V21,V22,V22bis 09 450 0200 |
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|
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WELCOME TO ZPM3 |
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~~~~~~~~~~~~~~~ |
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Welcome to the best CP/M compatible operating system for Z80 |
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based computers with banked memory. The best? Yes, we believe so. |
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CP/M 3.0 has had bad press, but the fact is that it is faster |
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than CP/M 2.2 ever was, and it offered more integrated |
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facilities. Perhaps it was all the Z80 replacement BDOSes for |
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CP/M 2.2 which stole the limelight from CP/M 3.0, or was it just |
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that few computers had the required banked memory? |
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|
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Whatever the reason for CP/M 3.0's lack of success in the |
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marketplace, there are still plenty of users who will stand by |
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its wonderful facilities and speed. For those users ZPM3 provides |
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the long awaited Z80 coded update. |
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|
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ZPM3 offers all the good things that CP/M 3.0 does, and then it |
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offers more. Because ZPM3 is written in Z80 code rather than the |
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8080 code of CP/M 3.0, it can do everything that CP/M 3.0 does, |
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but in much less space. With the extra space recovered, ZPM3 |
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packs in a number of new facilities. Yet the whole package fits |
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in exactly the same space as CP/M 3.0 so you can directly replace |
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your old CP/M 3.0 BDOS with ZPM3 without a worry. |
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|
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ZPM3 is also fast. Faster, in fact, than CP/M 3.0. This is |
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possible because the rich Z80 instruction set allows many |
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algorithms to be implemented more efficiently. In addition, the |
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extra space available in ZPM3 has been put to use to further |
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optimise the code. Lots of small optimisations smooth the |
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execution flow, so ZPM3 becomes the fastest operating system on |
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most banked CP/M computers. |
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|
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|
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THE FEATURES |
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~~~~~~~~~~~~ |
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ZPM3, in addition to complete CP/M 3.0 compatibility, offers the |
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following features: |
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|
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Random Read Bug fixed. |
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++++++++++++++++++++++ |
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Maybe you didn't know, but CP/M 3.0 has a bug. It affects random |
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reads under very specific circumstances, and can result in a |
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program thinking that you don't have some pieces of data in a |
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file when in fact you do. The bug would occur very, very rarely, |
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but it is real. ZPM3 finally squashes it. |
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|
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|
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Protected SCB User code |
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+++++++++++++++++++++++ |
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The System Control Block of CP/M 3.0 was a revolution at the |
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time. ZCPR has a system environment and most other operating |
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systems have other similar structures, but the SCB of CP/M 3.0 |
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was one of the very first. |
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|
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Unfortunately, Digital Research never properly documented it, and |
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some programmers found things out about it that weren't quite |
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true and started programming accordingly. As well, because it is |
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available in the TPA bank, runaway programs can overwrite it |
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causing problems. |
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|
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Mostly though, the SCB will survive, or at least any problems |
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will be so obvious that the user will realise that a crash has |
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occurred and will reboot. A real problem exists with the CP/M 3.0 |
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code however when the user value is written over with a value |
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above 15. Many programs now directly write to this byte, and if |
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they put a value in that is above 15, all sorts of havoc can |
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happen with the disk system. Actually, CP/M 3.0 will handle user |
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areas above 15 with this method, and all seems ok until the |
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operating system mistakes one of these directory entries as an |
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XFCB. Simply put, user areas above 15 must not be used with CP/M |
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3.0. |
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|
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ZPM3 has code which prevents these problems, making the system |
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even more stable. |
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Obsoleted Trap system. |
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++++++++++++++++++++++ |
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One of the problems of the banked operating system was that it |
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was possible to redirect the BIOS to code below common memory, in |
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which case the banked BDOS could not access it. One solution is |
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to call all BIOS code from common memory, but this involves a |
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bank switch for every BIOS call, and this slows things down |
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considerably. |
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|
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CP/M 3.0 got around the problem by providing special code just |
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below the SCB. If you redirected the BIOS, you also had to change |
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this code which caused a bank switch when your new BIOS routine |
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was called. When you removed the redirection, you also had to |
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restore the special code. |
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|
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This system has major drawbacks. For a start, if you redirect the |
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BIOS, then another program redirects your redirection, then you |
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remove your first redirection (along with the special code), the |
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bank switch won't happen for the second redirection and the |
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system will crash. |
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|
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If a CP/M 2.2 program tried to do the redirection, it would know |
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nothing about CP/M 3.0 and would not adjust the special code, so |
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a crash would result in that case too. |
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|
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The special code was called the "Trap System" as it was meant to |
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trap redirection (as long as you set the trap). ZPM3 has |
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eliminated the need for the traps. They are still there, and |
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programs can still fiddle with them, but it doesn't matter how |
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they are set, they are ignored. There is simply no need for them |
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anymore. And this has been achieved without a performance |
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penalty. In fact, in the case of a program which sets the traps |
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but forgets to restore them, performance is now much better. |
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|
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|
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Semi-Permanent Read Only status for drives. |
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+++++++++++++++++++++++++++++++++++++++++++ |
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In recent years, a trend in CP/M 2.2 is to make drives which have |
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been set read only to remain that way until explicitly changed by |
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function 37. ZPM3 now adopts this logic. Previously a control-C |
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would return a read only drive to read write. The advantage is |
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that a program can now make a drive read only for a session and |
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know that it will stay that way. |
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|
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|
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ZCPR compatible function 152 |
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++++++++++++++++++++++++++++ |
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Function 152 is the CP/M 3.0 parser. It was a great innovation at |
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the time as parsing is one of the more tedious aspects of |
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programming for CP/M. Unfortunately, almost as soon as it |
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appeared, it was made obsolete by the fact that it didn't handle |
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references to user number (DU references). A line such as |
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A:FILE.TYP would be correctly parsed, but A3:FILE.TYP would not. |
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CP/M 3.0 programs would often parse the drive and user |
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separately, then give function 152 the line without the DU: |
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reference. All this extra work should not have been necessary if |
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CP/M 3.0 had included user number parsing. |
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|
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ZPM3 parses the user number, and goes even further by handling |
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named directories for ZCPR. This is possible as long as you set a |
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special word in the SCB which tells ZPM3 where to find the ZCPR |
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system environment descriptor. ZCCP, a companion CCP for ZPM3, |
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handles this automatically, but for Z3PLUS users, a special |
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utility is available which automatically sets this word. |
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|
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The result is that CP/M 3.0 programs will not balk at DU: |
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references and ZPM3 aware programs can use the full DU: and DIR: |
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facilities of function 152. It has also made the brilliant ZCCP |
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code possible. |
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New Functions 54 and 55 |
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+++++++++++++++++++++++ |
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Datestamps in CP/M 3.0 are wonderful, but difficult to |
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manipulate. Two new functions make them easier to handle and at |
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the same time give compatibility to Z80DOS aware programs. |
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Function 54 (Get Stamp) returns a Z80DOS compatible datestamp. |
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Any program (such as many directory programs) which recognise the |
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Z80DOS standard can make use of function 54. There is only one |
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slight difference between Z80DOS datestamps and ZPM3's which you |
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should be aware of. Z80DOS will return a correct datestamp after |
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any successful open or search of any extent. ZPM3 can only return |
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a correct datestamp after a successful open or search of the |
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first extent of the file. This is because CP/M 3.0 datestamps are |
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only saved for the first extents of each file, in order to |
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provide the highest performance. |
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|
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Even more interesting is Function 55 (Use Stamp) which provides a |
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mechanism for changing datestamps on files. Trying to do this |
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with CP/M 3.0 was virtually impossible because it involved direct |
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sector writes. With Function 55 you can simply set the stamp and |
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then write. |
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Wheel protected files |
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+++++++++++++++++++++ |
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If you are using a ZCPR system (ZCCP or Z3PLUS), ZPM3 has access |
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to the wheel byte and supports wheel protected files. Such files |
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act normally if the wheel is set (signifying a priveleged user), |
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but if the wheel is not set, the files can not be changed. This |
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is of most benefit to BBS systems. The implementation is |
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virtually the same as most current Z80 CP/M 2.2 compatible |
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BDOSes. |
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Better error messages |
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+++++++++++++++++++++ |
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CP/M 3.0 introduced the best error messages that CP/M had ever |
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had. ZPM3 goes further. The main difference you will notice is |
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that the user number as well as the drive is shown in the error |
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message. This is invaluable in helping you identify which file |
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might have caused a problem. |
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|
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Function 10 history buffer and improved editing. |
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++++++++++++++++++++++++++++++++++++++++++++++++ |
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Function 10 is used by the CCP to input command lines. Many other |
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programs use function 10 for input. |
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CP/M 3.0 introduced a history buffer for function 10. You press |
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control-W and you were returned the last command. It is a great |
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facility, but because it only remembers one command it is rather |
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limited. There have been RSXes written which give a much larger |
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history buffer, but RSXes take up extra program memory so are |
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undesirable. |
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ZPM3 gives a large (approximately 250 bytes) history buffer which |
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can store multiple commands. It also makes very intelligent use |
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of the buffer so that identical commands are not stored twice, |
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and commands of less than three characters are not stored. The |
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history buffer takes up no additional memory, and is always |
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available. |
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|
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For security, it is possible to clear the history buffer so that |
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other users can not see what commands you have used. |
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The ZPM3 history buffer feature is so good, that for many users, |
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the ZPM3 upgrade is completely justified by it. |
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As part of the history buffer system, ZPM3 also offers a facility |
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called Automatic Command Prompting. This can be disabled, or can |
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be made switchable from the keyboard. When it is on, ZPM3 tries |
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to fill in the rest of your command based on what commands you |
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used most recently. It is like magic, and can save you typing out |
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complicated commands many times. In effect, it looks through the |
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history buffer for you and finds the command it thinks you want. |
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As you keep typing, if it turns out that the command doesn't |
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match anymore, it will try to match another command, and if it |
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can't, it lets you make the command by yourself. This facility is |
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quite amazing to watch. |
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|
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And to integrate the history buffer and the automatic command |
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prompting, function 10 has the best command line editing you'll |
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find anywhere. Most of the control keys do something when you are |
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editing a function 10 line, and for the most part they mimic the |
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standard WordStar/NewWord/ZDE functions. You can jump to |
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different words in the command, delete individual words, delete |
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individual letters, insert letters, and a whole lot more. |
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Here is a list of what the various control keys do for function |
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10: |
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A Move left one word |
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B Go to the beginning or end of the line |
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C Warm boot if at start of line, otherwise nothing |
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D Go right one character |
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E Go backwards one command in the history buffer |
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F Go right one word |
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G Delete current character |
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H Destructive backspace |
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I |
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J Enter line |
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K Delete all to the right |
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L |
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M Enter line |
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N |
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O |
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P Toggle printing |
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Q Toggle automatic command prompting (if enabled) |
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R |
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S Go left one character |
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T Delete current word |
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U Add current line to history buffer |
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V Clear line and delete from history buffer |
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W Go forwards one command in the history buffer |
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X Delete all to the left |
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Y Clear the whole line |
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Z |
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CPMLDR.REL bug fixed. |
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+++++++++++++++++++++ |
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If you have ever tried to use the CPMLDR.REL code supplied with |
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CP/M 3.0 to load a CPM3.SYS file larger than 16k, you have |
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probably come across the CPMLDR.REL bug. The computer probably |
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crashed, and you were left wondering what you did wrong in your |
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bios. |
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|
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Well CPMLDR.REL has a bug. To solve this for you ZPM3 comes with |
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ZPM3LDR.REL which directly replaces CPMLDR.REL. It is also |
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somewhat better in that all the messages, and the fcb for loading |
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CPM3.SYS, are at the start of the file along with plenty of spare |
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room. As a result you can easily patch the signon and error |
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messages to say whatever you like and even change the FCB to load |
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a file called something other than CPM3.SYS. |
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All About the Random Read Bug. |
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============================== |
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Never heard of it? Well it's there in CP/M 3.0. I spent a lot of |
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time trying to work out what it was and just why it was |
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happening, and if you are interested, here are the details. |
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|
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CP/M 3.0 uses the Record Count byte of an active FCB a little |
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differently from the way CP/M 2.2 does. It is mentioned in the |
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CP/M 3.0 manuals that the record count may contain numbers |
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greater than 128, but in such a case it implies that the record |
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count is really 128. CP/M 2.2 would not return record counts |
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greater than 128. |
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The reason for the use of the record count in this way is to help |
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speed up some of the logic used to find records in a file. It |
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works very well for sequential access. When it comes to random |
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access, the system has some failings. |
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|
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The idea behind CP/M 3.0's unusual use of the record count is to |
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keep the record count of the last logical extent of the current |
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physical extent always in the Record Count byte. When accessing |
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extents before the last one, bit 7 of the byte is set. That way |
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it will always be at least 128 for logical extents before the |
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last (which CP/M 3.0 translates to mean equal to 128), and the |
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lower 7 bits are used as convenient storage for the record count |
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of the last logical extent. This is particularly convenient |
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because it means there is no need to go and read the directory |
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entry again when it comes time to read the last logical extent. |
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I hope you have followed that! In sequential access, this scheme |
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is great. The problem occurs with random access. In this case it |
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is possible to access a logical extent which has no records in |
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it. This could be any logical extent past the last one. In such a |
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case the record count must be returned as 0 (which is correct). |
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If we then go back to a previous logical extent in the same |
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physical extent, CP/M 3.0 gets confused and assumes that there |
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must be 128 records in that extent because the one we just came |
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from had no records and we are now accessing an earlier extent. |
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You're probably well and truly lost by now! |
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|
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Anyhow, the assumption that CP/M 3.0 makes is quite wrong. The |
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record count ends up being set to 128, a read is allowed to go |
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ahead as if nothing was wrong, no error is returned, and the |
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record count remains incorrectly set until a different physical |
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extent is opened. The result could be chaos, but mostly it just |
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means that a program returns the wrong information. |
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|
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Remember, a logical extent is always 16k. A physical extent can |
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be a multiple of 16k and is all the data described by one |
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directory entry. If your system has physical extents which are |
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16k, you would never have the problem because a new physical |
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extent would be properly opened for every new logical extent that |
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was accessed. |
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|
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Typically though, a physical extent is 32k, so it holds 2 logical |
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extents. The problem won't arise until the file grows past the |
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32k mark in such a case. And when the file gets over 48k the |
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problem can't occur again until it gets over 64k... and so on. |
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Even then, it can only happen if reads are attempted to |
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particular extents in a particular order. So you shouldn't be too |
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surprised if the bug hasn't been too noticeable to you. |
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|
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ZPM3 squashes the bug once and for all by using the correct |
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logic. In the situation where the bug would normally occur, ZPM3 |
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makes sure it gets the correct record count information, and the |
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reads return the correct record count every time. |
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|
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If you are interested in seeing a demonstration of the bug in |
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action (on CP/M 3.0) and comparing it with ZPM3, there is a file |
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floating around various bulletin boards which contains |
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demonstrations for the bug and an RSX to fix it. The RSX is a |
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less than perfect way of overcoming the bug, although it seems to |
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work. However, now that you have ZPM3, you don't need to worry. |
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|
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Other things you should know about ZPM3 |
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======================================= |
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ZPM3 has worked on EVERY CP/M 3.0 system tried so far except one. |
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This is a Bondwell computer, and as yet it isn't clear why it |
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won't work. I will study the source code of its BIOS and come up |
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with a fix shortly. |
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|
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The MAKEDOS.COM utility is not perfect (as mentioned previously) |
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and it seems that nobody has managed to get it to work with the |
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Commodore C128 system. You must use the conventional method for |
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installing ZPM3 on such systems. |
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|
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If you have a computer that ZPM3 will not install on with MAKEDOS |
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and you do not have access to the files required to do a |
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conventional install, please contact me. I am interested in |
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making ZPM3 as universal as possible and will help you to install |
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it on your system. |
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|
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The ESCAPE key is ignored by function 10. There has been some |
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lively discussion about this but the decision is final: it stays |
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ignored. Remember what function 10 is for and you will understand |
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why I made it ignore the ESCAPE key. The argument against this |
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has been from people who control their terminals from the command |
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line. Apparently some people type in an escape sequence at the |
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command line (which CP/M 3.0 will not output correctly anyhow |
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(converting the escape character to ^[)) then press return to |
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have the CCP echo back the line including the escape character. |
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|
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Sorry folks, that is a KLUDGE in my books! Anybody using Z-System |
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would of course use an ALIAS and ECHO to do this properly, but |
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for those who will continue to complain that I have sacrificed |
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CP/M 3.0 compatibility I am now including ECHOTERM.COM to solve |
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your problems. Run it and whatever you type will be sent to the |
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terminal correctly after you press RETURN. Press RETURN twice to |
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exit the program. |
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|
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And a reminder that the ability to put control characters into |
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function 10 lines was always limited by the fact that some |
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control keys were used to edit the command line. CP/M 3.0 added |
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even more, and ZPM3 uses virtually all the control keys. The few |
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that aren't used are ignored, and this is in fact a FEATURE which |
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guarantees that unusable characters can't get into function 10 |
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lines by accident. |
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|
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|
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|
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|
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LEGALS and SUCH |
|||
=============== |
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The ZPM3 package is supplied free of charge, on the condition |
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that you don't use it to make money. If you want to use it |
|||
commercially you must contact me to get the OK (and negotiate our |
|||
fee). |
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|
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If you find anyone (except myself) charging money for ZPM3, |
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please inform me! |
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|
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Nobody is making any guarantees about this software. None at all. |
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If it causes your house to burn down, or a divorce, or just a bad |
|||
day, this is unfortunate, regrettable, but there is nothing that |
|||
I can or will do about it. You have been warned. |
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|
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The ZPM3 package must only be distributed in the form that you |
|||
found it. Do not change or add anything. Don't even change it |
|||
into a different type of archive. Just leave it alone. However |
|||
you are free to distribute it to as many places and people that |
|||
you can. Just don't charge for it. |
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|
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|
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|
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If in using ZPM3 you find that it doesn't act as described, |
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please forward the details to me so that either the ZPM3 code or |
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the documentation can be changed. If you would like further |
|||
details, please forward your specific questions to me. SJC. |
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|
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|
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|
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|
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As a service to all our ZPM3 fans, the latest version of the ZPM3 |
|||
package can now be ordered. At this stage we can only supply IBM |
|||
formatted 3.5 inch 720k disks, however if you are keen enough |
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that shouldn't matter. ZPM3 remains free, however this service |
|||
will cost you $15 Australian (for the disk, copying, postage and |
|||
packing) to most places in the Western World (others by |
|||
arrangement). |
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|
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This is a good way to guarantee you have the latest version, and |
|||
to guarantee that your package has not been corrupted by some |
|||
unscrupulous person. |
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|
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When we fill your order, we will make sure to include the latest |
|||
demonstration copy of MYZ80 - the fastest and best Z80 emulator |
|||
for IBM AT (and better) compatibles. MYZ80 can run ZPM3 with |
|||
ease. It also handles ZCPR and CP/M 2.2. And yes, we do mean |
|||
FASTEST. |
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|
|||
Send your international money order to: |
|||
|
|||
Software by Simeon |
|||
ZPM3 Package |
|||
2 Maytone Ave |
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Killara NSW |
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Australia 2071 |
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|
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Your order will be promptly filled. |
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