Project to modify MDOS to make GPL resident
-------------------------------------------
Tony Knerr   August-October 2010
--------------------------------
 
1. INITGPL
 
INITGPL is a modified version of GPL. It is run once after MDOS has booted
to load the TI ROM and GROM files and make the necessary patches for use with
the Geneve. It also loads the program GPL Cheater into page >31 for instant
access with the MDOS command GPL. It sets the GPL loaded flag in MDOS. After
running, it restarts MDOS.
 
2. GPLTEST
 
GPLTEST is a program that reads the GPL (previously TIMODE) flag in MDOS to
determine whether INITGPL has been previously run. The flag is on memory
page >00 at offset >0126. GPLTEST will return a "Y" into the %1 variable
if that lcation contains the value >FFFF. The code "IF %1==Y goto xxxx" is
used as the next line in Autoexec where "xxxx" is a point where the loading of
INITGPL can be skipped.
 
3. TILINK
 
TILINK is the special linker for producing the GPL or GPLCHEATER files.
It normally produces a protected file with a load address of >0401. The
protection scheme has been removed so that a version of GPLCHEATER can be
produced which can be stored and run from memory page >31. When producing
the file GPL, the first byte of the file header must be manually changed
to >FF in order to load the subsequent GPM, GPN, GPo, & GPP files.
 
4. MDOS
 
MDOS has been modified in several ways.
 
The command "GPL" has been added. GPL instantly activates the program
GPL CHEATER by Tim Tesch stored in page >31 by the INITGPL program.
The GPL command will also load a cartridge from the command line if the 
filename is typed after the command on the same line. Example: "GPL HDS1.XB",
without the quotes.
 
The TIMODE flag is now used to determine whether GPL has been pre-loaded.
 
TIMODE has been made permanent. Changes documented as follows:
 
\HEAD\BATCMDS
 
* Comment out or delete all lines between "AUTTIM MOV  R11,R10" and "B    *R10"
  (line "B   *R10" is right before "TIMPAG BYTE >3F,>3E,>3D,>3C")
 
\HEAD\HCLIS
 
* Comment out or remove line "CLR  @GPLPAR"
 
\HEAD\HPAGES
 
* Insert the following lines after the line "BYTE P_RESV            BWM  8.24.92
     FOR TIMODE PERM FIX"
 
       BYTE >3F,>3E,>3D,>3C
       BYTE >3B,>3A,>39,>38
       BYTE >37,>36,>35,>34
       BYTE >33
       BYTE >EC,>ED,>EE,>EF
       BYTE >28,>29,>2A,>2B
       BYTE >2C,>2D,>2E,>2F
 
\HEAD\OSTASK
 
* Change the data in line "GPLPAR DATA 0            STRING TO CONTROL SPEED OF
  GPL INTERPRETER" from 0 to >FFFF
 
\HEAD\OSHEAD1S
 
* Change the data in line "GPLPAR DATA 0            STRING TO CONTROL SPEED OF 
  GPL INTERPRETER" from 0 to >FFFF
 
\HEAD\TASKHEADS
 
* Change the data in line "GPLPAR DATA 0            STRING TO CONTROL SPEED OF 
  GPL INTERPRETER" from 0 to >FFFF
 
5. GPL, GPLCHEATER, and EXEC
 
These 3 programs have been modified to restart MDOS when exiting. MDOS
does not allow them to continue in a batch file that they are run from,
so this is the next best alternative.
 
The following code replaces the normal "BLWP @>0000" code for exiting:
 
*
RSTART LWPI >F000
       LI   R14,CODSTR
       LI   R15,>F020
LOOPZZ MOV  *R14+,*R15+
       CI   R14,CODEND
       JNE  LOOPZZ
       B    @>F020
CODSTR LIMI 0
       CLR  @>F110
       BLWP @0
CODEND DATA >0000
*
 
6. TI GROM0 file
 
The TI GROM0 file, normally named GPN,(or INITGPN in the INITGPL series of
files) has been modified to add an additional menu entry.
"1 FOR RETURN TO MDOS" is now the first menu entry. This provides a quick and
easy return to MDOS.
You can also type "CALL MDOS" from TI BASIC or any of the Extended Basics to
return to MDOS. 
 
7. CLEARGPL
 
The program CLEARGPL is used for testing purposes. It clears the GPL LOADED
flag in MDOS.