Date: Sat, 17 Aug 96 18:07:50 +0600 From: Pulthar@nietzsche.execpc.com Subject: Re: GeoBasic Here's the more technical info I have on geoBasic. I've posted it to comp.sys.cbm as well. geoBasic Module Definitions: VLIR # Constant Loads @ Description ------ -------- ------- ----------- 0 R_MAIN $0400 Resident code. Two JMP's @ $0400 then skip to $07fc to leave room for screen memory. This module contains all the code that must always be available. All the other modules use the subroutines contained here. 1 R_FILE $4ec7 High level disk file stuff (Rename, Open, etc). 2 R_DA *$75d8 Run's DA's. *Loads inside FG_BUFFER on 64 or SCREEN_BASE on the 128. This keeps it from overwriting Basic's code. 3 R_INIT $4ec7 geobasic Initialization code. Loaded from Resident code. 4 R_LOAD $7501 Basic Program loader. Loads into FG_BUFFER (see R_DA). 5 R_BINT $4f96 Interpreter (BasRes). This is the module that actually runs the user's program. 6 R_BINT2 $0400 7 R_FONT $6f8b Font Manager (cFont, cSysInfo, and GetDiskBitmap). 8 R_DISK $6f8b Lower level disk stuff (reading bytes, etc). 9 R_PRINT $6f8b Printer Routines. 10 R_MENU $4ec7 Menu Utility. 11 R_DBOX $4ec7 Dialog Box Utility. 12 R_ICON $4ec7 Icon Utility. 13 R_BMAP $4ec7 Bitmap Utility. 14 R_SPRT $4ec7 Sprite Utility. 15 R_EDIT $4503 Editor. 16 R_APPL $4b00 Make Application (run-time). 17 R_DEBUG $47cc Debugger. GB Program, Disk Layout Records 0 to 9 - left empty to leave room for GB code when making run-time. Record #10 - VLIR table. Keeps track of what modules hold what line #'s. Used for doing the VLIR splitting. The table is a single sector and there is one eight byte entry for each program module. The entries have the following format: .word ? ; Highest line number in module. .word ? ; Length_of_module (in bytes) .byte ? ; nesting_level .byte ? ; write_status .byte ? ; modified_status .byte NULL ; terminator The very first entry is a bit different. It looks like this: .word ??? ; (NULLS) .byte x ; number of entries in the VLIR table (not ; counting this one which is entry #0). .byte x ; number of labels in the label table (minus 1, ; labels are numbered from zero!). If there ; are no labels then it equals $ff. .byte $f0? .byte $f6? .word ??? Record #11 - Object table. All of the geos objects are store in this record, one right after the other. Record #12 - Label Table. Here is where the labels (@xxxx and object names) are stored. Each label entry is 8 bytes long and has the following format: For @ labels: .block 6 ; label name padded with NULLs .word line_number For object labels (i.e. bitmaps, menus, icons, etc.): .byte type ; $80 = Menu ; $81 = DB ; $82 = Icon ; $83 = Sprites ; $84 = Bitmap .block 5 ; object name padded with NULLs .word address ; where in memory the object is located. Record #13 onward - Holds the basic program lines. Each line has the following format: .byte ; length_of_line .word ; line_number .block ??? ; now comes the tokenized text Record #126 backward - Disk loadable bitmaps are stored beginning at record #126. Additional bitmaps are added backwards until they meet up with the program records. Note that only disk loadable bitmaps are stored here. Regular bitmaps are stored in the Object Table (record #11). Getting Registers after a CALL: After using the CALL command use can get the return values of the registers by PEEKing the following memory locations: A = $28a (650) X = $28b (651) Y = $28c (652) SR = $28d (653) POP Command: The old (V1.0) Pop command had several serious bugs that caused a system crash. POP Command: The old (V1.0) Pop command had several serious bugs that caused a system crash. The new version works like this: executing a POP will remove the current GOSUB/WHILE/REPEAT stack frame. In other words it will allow you to 'forget' that you are in a subroutine or loop (this does not apply to a FOR...NEXT loop). One thing to keep in mind is that after executing a POP you must not allow the program to reach the RETURN/LOOP/UNTIL commands. The best way of doing this is with a construct like this: 10 GOSUB DoSomething 20 END 30 50 @DoSomething 60 <various commands> 70 IF something = error THEN POP : GOTO @DoError 80 RETURN 90 100 @DoError 110 .... etc Of course if you are two levels deep in a subroutine and execute a POP, then you execute a RETURN the program will return TWO levels back rather then just one. Could come in handy at times. GB Variables - zero page Name Address Size Description ---- ------- ---- ----------- basCur $81/129 word current character in basic memory basBegin $83/131 word pointer to beginning of basic basicEnd $85/133 word pointer to beginning of labels (minus 1 for end of basic) varBegin $87/135 word pointer to the beginning of variables arrayBegin $89/137 word pointer to the beginning of arrays arrayEnd $8b/139 word pointer to the end of arrays arrayLength $8d/141 word length of array/temporary register strnBegin $8f/143 word pointer to the beginning of strings arrayLength $8d/141 word length of array/temporary register strnBegin $8f/143 word pointer to the beginning of strings zeroShift $91/145 byte used by floating point routines dec_pt $92/146 byte used by floating point routines varPtr $93/147 word pointer to value of variable machine_type $95/149 byte 0 if c64, $80 if 128 strnStack $96/150 9 bytes stack for three temp string descriptors strnStkIndx $9f/159 byte index into strnStack prevStrnStkIndx $a0/160 byte previous strnStack index rdIndex $a1/161 byte index to reading in strings gax2 $a2/162 word (not commented in source code) curStrn $a4/164 word pointer to most current string that was added or moved. strnDes $a6/166 word pointer to string descriptor descPtr $a8/168 word pointer to string descriptor for string operations. geosBegin $aa/170 word pointer to the beginning of object (menus, icons, etc.) data. memAmnt $ac/172 word amount of memory to insert or delete curKeyBrdPos $ae/174 word (not commented in source) SetForIOTemp $b0/176 word (not commented in source) curLineNum $b2/178 word current line number being executed or $ff in direct mode VLIRtabl $b4/180 word pointer to beginning of VLIR table xPos $b6/182 word X position for PRINT yPos $b8/184 byte Y position for PRINT opMask $b9/185 byte current comparison being performed >/1, =/2, </4 or any combo of these comm_Flag $ba/186 byte flag for which command is currently being executed: 0 = none, 1 = RUN, -1 = LIST - used by the Editor dataPtr $bc/188 word pointer in basic to DATA statements FP_sgns $be/190 byte temp flag for sign of FP number exp_found $bf/191 byte flag for whether exponent was found fontBegin $c0/192 word pointer to beginning of font lastFontPtr $c2/194 word (not commented in source) curDBPtr $c4/196 word pointer to current dialog box data sprite stuff $c6/198 36 bytes internal sprite variables r16 $ea/234 word more registers r17 $ec/236 word r18 $ee/238 word r19 $f0/240 word r20 $f2/242 word r21 $f4/244 word numDim $f6/246 byte number of dimensions in array grbackground $f7/247 byte FG/BG colors of graphics screen dig_found $f8/248 byte flag for whether a digit was found when converting strings to FP operand_mask $f9/249 byte >/1, =/2, </4 strnFlag $fa/250 byte $ff if string expected, else 0 ************************************************************************ Glenn Holmer (ulthar@execpc.com) Q-Link: ShadowM This is a text....
Amiga7878