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CPM OPERATING SYSTEMS/CPM.Z80.DE/PERSONAL/PCPM-86/BDOS 4.1/readme.txt

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+BDOS 4.1 source tree
+====================
+
+  This file contains disassembled source code and a build system for the 
+CP/M-86 BDOS, version 4.1. This is the version that is included in 
+Personal CP/M-86 2.x and also DOS Plus 1.2.
+
+How to build
+============
+
+  In order to use the build system, you will need:
+* The Digital Research assembler and linker: RASM86 and LINKEXE.
+* Pacific C, to build the C tools EXE2CMD and DPGEN.
+* GNU Make.
+
+  You should just be able to type 'make' and a new system file (new.sys)
+will be generated containing the newly-built BDOS.
+
+  Note, however, that certain structures need to be paragraph-aligned, and 
+the A86 files do not enforce this. Therefore if you add or remove 
+code or variables, you will need to check for bits marked PADDING and ensure
+they do pad out the correct number of bytes.
+
+Notes on the source
+===================
+
+  The source code was disassembled using the IDA disassembler. It has been
+split up into modules named after their counterparts in Concurrent CP/M
+(SUP, RTM etc.) plus a few extras.
+
+  Rather than use LINKCMD to generate a CMD file, I was forced to use 
+LINKEXE to generate an EXE, and then write a custom EXE2CMD program to 
+convert the one to the other. This is because LINKCMD starts the data 
+segment at offset 100h, but to build the BDOS you need it at 0. The 
+'official' DRI way of doing this involves a patched linker (LINK0.CMD) but
+there's no DOS version and it didn't seem to like running in a CP/M emulator,
+so I was forced to adopt other tactics.
+
+  There are two variables which, despite being in the BDOS data segment, refer 
+to addresses in the XIOS. These are:
+
+freemem:	The address of the first segment available for programs. This
+		is left as an unresolved external symbol in the provided 
+		source code, and is populated by DPGEN.
+
+bdos_sysflags:	The address of the system flag table in the XIOS. The only
+		way I found of making that come out right was to store its
+		value as an EQU directive in SYSTEM.A86. When I was writing 
+		my modified XIOS for DOS Plus, I came across the same problem
+		from the other direction; the modified XIOS initialises this
+		variable at startup time so that the value in the BDOS is no 
+		longer relevant.
+
+Support for multiple versions
+=============================
+
+  The build system is currently configured to build Personal CP/M v2.04e. If 
+you want to build other versions:
+
+1. Get hold of the .SYS file for the version you want to build.
+2. Use DPSPLIT (not supplied) to break it into BDOS.CMD, XIOS.CMD and CCP.CMD.
+  Delete BDOS.CMD but hang on to the other two.
+3. Copy the correct SYS*.A86 to SYSTEM.A86, and the correct SER*.A86 to 
+  SERIAL.A86:
+
+System		Version		Language	Files to copy
+==========================================================================
+PCP/M		2.02		German		SER202D.A86 / SYS202D.A86
+PCP/M		2.02		English		SER202E.A86 / SYS202E.A86
+PCP/M		2.04		German		SER204D.A86 / SYS204D.A86
+PCP/M		2.04		English		SER204E.A86 / SYS204E.A86
+PCP/M		2.11		German		SER211D.A86 / SYS211D.A86
+PCP/M		2.11		English		SER211E.A86 / SYS211E.A86
+DOS Plus	1.2		English		SERDOSP.A86 / SYSDOSP.A86
+
+4. Rerun the build.
+
+  From the point of view of the BDOS, the changes are mostly trivial: 
+differences are mostly caused by such things as a different serial number,
+alternative screen dimensions etc. One exception is that DOS Plus omits a
+few BDOS patches which are present in all known PCP/M-86 2.x versions.
+