RomWBW/Source/pSys/ReadMe.txt

This directory contains a port of p-System IV.0 for RomWBW.



It was derived from the p-System Adaptable Z80 System.  Unlike some 

other distributions, this implements a native p-System Z80 Extended 

BIOS, it does not use a CP/M BIOS layer.



Files:



loader.asm     p-System primary loader for RomWBW

bios.asm       p-System BIOS for RomWBW HBIOS source (TASM)

biostest.dat   binary image of SBIOSTESTER

boot.dat       binary image of p-System bootstrap

psys.vol       first (boot) slice, all p-System dist files

blank.vol      a generic blank p-System volume

fill.asm       used to complete the track 0 build (see below)



Notes:



This adaptation runs on a single RomWBW HBIOS hard disk type device (CF 

Card, SD Card, IDE drive, etc.).  The image built (psys.img) should be 

copied to your disk media starting at the first sector.  You can then 

boot by selecting the corresponding disk device unit number from the 

RomWBW boot loader prompt.  The p-System disk image (psys.img) is 

entirely different from the RomWBW CP/M-style disk images.



The boot device hard disk is broken up into 6 logical p-System 

volumes.  These are referred to as p-System slices.  A single RomWBW 

disk device can contain either CP/M-style slices or p-System slices, 

but not both. Each p-System slices is exactly 8 MB and support for 

exactly 6 slices is provided.



The first track of each volume contains all of the code required to 

boot the p-System.  However, the assignment of the volumes is always in 

the order that the slices appear physically on the hard disk device.  

Normally, you would just boot to slice 0 from the RomWBW Boot Loader.



The first track contains the following:

 - 4 sector p-System primary loader for RomWBW HBIOS

 - 1.5 sector p-System BIOS for RomWBW HBIOS

 - 4 sector p-System bootstrap

 - 6.5 sector filler to complete a full track



The p-System bootstrap is a binary image provided in the p-System 

distribution.  The loader and the BIOS are custom for RomWBW and the 

source is provided here.



The layout of the first track does not conform exactly to the 

recommended p-System layout.  The recommended layout is not possible 

because it conflicts with the RomWBW definition for a boot track.  

However, the changes are only slightly different sector assignments for 

the different boot components -- the general boot sequence and mechanism 

for the p-System is completely standard.



The logical disk geometry used by this p-System

adaptation is:

 - 512 byte sector length

 - 16 sectors per track

 - 192 tracks per disk



This layout does not occupy the full 8MB slice size allocated.  This is 

to allow for future expansion of the filesystems.



The p-System distribution includes a BIOS tester that is provided as a 

binary image.  This tester was used to test the BIOS code in this 

adaptation.  It turns out that this code has a blatant error that

causes it to fail for 512 byte sector sizes (which are allowed).

To resolve this, biostest.dat was disassembled and patched to correct

the error.  The original version is retained as biostest.old.



The boot disk provided here was constructed by simply copying all of 

the content from the p-System distribution disks onto the boot disk.  

SYSTEM.MISCINFO was updated for an ANSI terminal.  The GOTOXY routine 

in SYSTEM.PASCAL was also updated for an ANSI terminal. Note that the 

BIOS conwrit routine is hacked to add a '[' to any output escape 

character.  This is needed because p-System has a very limited terminal 

escape sequence handling configuration.  The debugger code as added to 

SYSTEM.PASCAL to enable the debug function.  SYSTEM.INTERP was modified 

to enable the extended BIOS functions.



The build/makefile creates the psys disk image (psys.img) by 

concatenating psys.vol and blank.vol (after adding track 0 contents to 

each).  psys.vol and blank.vol are recognized by CiderPress and 

CiderPress can be used to add/remove files from these volumes.  

To extract volumes from a disk image, Andrew Davidson has created

a nice Python script that can extract p-System volumes from an

existing disk image file.  The extracted volume can be manipulated

by CiderPress.  The script is also capable of re-inserting a modified

volume back into the disk image file.  This tool is available at:

https://github.com/robosnacks/psysimg.



There is currently no support for floppy drives.



Wayne Warthen

wwarthen@gmail.com



5:42 PM Sunday, January 15, 2023



So, it turns out that the serial line support in p-System is seriously 

deficient.  It insists on polling all of the serial input devices 

(console, remote, and printer) when the sytem is idle with the idea 

that it will queue up any characters received.  I guess the idea is 

that this will help in scenarios where characters are coming in too 

fast to be processed. However, the basic/default interpreter does not 

support the queues! Strangely, it still polls the devices and 

literally discards anything received.  This completely undermines the 

ability of the underlying hardware which is doing it's own robust

interrupt or hardware based buffering and flow control.



I have relinked the interpreter (SYSTEM.INTERP) so that it now uses

the BIOS version that supports the queues (BIOS.CRP).  This mostly

resolves the situation, but needlessly increases the size of the

interpreter.  Additionally, I believe that if the p-System queue gets

full, it will still poll and discard any new characters received.  I

have not seen any documentation indicating the size of the queues.



Seriously, what were they thinking.



One last thing in case anyone actually reads this.  As indicated

above, this is an adaptation of p-System IV.0.  It is well documented

that SofTech produced a IV.1 with some nice enhancements (like

subsidiary volumes and decent support for ANSI/VT-100 terminals).  I

have been unable to track down the IV.1 distribution media despite

trying very hard.  If anyone knows of a source for the media of the

Adaptable p-System for Z80, I would love to get hold of it.



3:58 PM Tuesday, January 17, 2023



I forgot to discuss the terminal handling.



The p-System has a setup program (SETUP.CODE) that is used to define

terminal handling escape sequences.  However, it is limited to a

single character to introduce the escape sequences.  Since ANSI

and VT-100 escape sequences start with 2 characters, this is

problematic.  The BIOS for RomWBW borrows a hack used by Udo Monk.

Specifically, whenever an outbound <esc> is seen, a '[' is added

in flight.



Likewise, it is problematic to define a way to interpret the

arrow keys transmitted by an ANSI/VT-100 terminal.  In this case,

the setup program was used to define up/down/left/right like

WordStar does: ^E,^X,^S,^D.



5:48 PM Tuesday, January 17, 2023



Updated instructions above to include a reference to Andrew 

Davidson's Python script that will extract/insert volumes from/to

a disk image.



1:31 PM Thursday, May 11, 2023