Routines
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04770: THE 'MAIN EXECUTION' LOOP
Used by the routine at MAIN_ADD.
The main loop controls the 'editing mode', the execution of direct commands and the production of reports.
MAIN_EXEC 04770 LD (IY+49),2 The lower part of the screen is to be two lines in size (see DF-SZ).
04774 CALL AUTO_LIST Produce an automatic listing.
This entry point is used by the routine at NEW.
MAIN_1 04777 CALL SET_MIN All the areas from E-LINE onwards are given their minimum configurations.
MAIN_2 04780 LD A,0 Channel 'K' is opened before calling the EDITOR.
04782 CALL CHAN_OPEN
04785 CALL EDITOR The EDITOR is called to allow the user to build up a BASIC line.
04788 CALL LINE_SCAN The current line is scanned for correct syntax.
04791 BIT 7,(IY+0) Jump forward if the syntax is correct (ERR-NR is 255).
04795 JR NZ,MAIN_3
04797 BIT 4,(IY+48) Jump forward if other than channel 'K' is being used (bit 4 of FLAGS2 is set).
04801 JR Z,MAIN_4
04803 LD HL,(23641) Point to the start of the line with the error (E-LINE).
04806 CALL REMOVE_FP Remove the floating-point forms from this line.
04809 LD (IY+0),255 Reset ERR-NR and jump back to MAIN_2 leaving the listing unchanged.
04813 JR MAIN_2
The 'edit-line' has passed syntax and the three types of line that are possible have to be distinguished from each other.
MAIN_3 04815 LD HL,(23641) Point to the start of the line (E-LINE).
04818 LD (23645),HL Set CH-ADD to the start also.
04821 CALL E_LINE_NO Fetch any line number into BC.
04824 LD A,B Is the line number a valid one?
04825 OR C
04826 JP NZ,MAIN_ADD Jump if it is so, and add the new line to the existing program.
04829 RST 24 Fetch the first character of the line and see if the line is 'carriage return only'.
04830 CP 13
04832 JR Z,MAIN_EXEC If it is then jump back.
The 'edit-line' must start with a direct BASIC command so this line becomes the first line to be interpreted.
04834 BIT 0,(IY+48) Clear the whole display unless the flag (bit 0 of FLAGS2) says it is unnecessary.
04838 CALL NZ,CL_ALL
04841 CALL CLS_LOWER Clear the lower part anyway.
04844 LD A,25 Set the appropriate value for the scroll counter (SCR-CT) by subtracting the second byte of S-POSN from 25).
04846 SUB (IY+79)
04849 LD (23692),A
04852 SET 7,(IY+1) Signal 'line execution' (set bit 7 of FLAGS).
04856 LD (IY+0),255 Ensure ERR-NR is correct.
04860 LD (IY+10),1 Deal with the first statement in the line (set NSPPC to 1).
04864 CALL LINE_RUN Now the line is interpreted. Note: the address MAIN_4 goes on to the machine stack and is addressed by ERR-SP.
After the line has been interpreted and all the actions consequential to it have been completed a return is made to MAIN_4, so that a report can be made.
MAIN_4 04867 HALT The maskable interrupt must be enabled.
04868 RES 5,(IY+1) Signal 'ready for a new key' (reset bit 5 of FLAGS).
04872 BIT 1,(IY+48) Empty the printer buffer if it has been used (bit 1 of FLAGS2 set).
04876 CALL NZ,COPY_BUFF
04879 LD A,(23610) Fetch the error number (ERR-NR) and increment it.
04882 INC A
This entry point is used by the routine at REPORT_G.
MAIN_G 04883 PUSH AF Save the new value.
04884 LD HL,0 The system variables FLAGX, X-PTR-hi and DEFADD are all set to zero.
04887 LD (IY+55),H
04890 LD (IY+38),H
04893 LD (23563),HL
04896 LD HL,1 Ensure that stream 0 points to channel 'K' (see STRMS).
04899 LD (23574),HL
04902 CALL SET_MIN Clear all the work areas and the calculator stack.
04905 RES 5,(IY+55) Signal 'editing mode' (reset bit 5 of FLAGX).
04909 CALL CLS_LOWER Clear the lower screen.
04912 SET 5,(IY+2) Signal 'the lower screen will require clearing' (set bit 5 of TV-FLAG).
04916 POP AF Fetch the report value.
04917 LD B,A Make a copy in B.
04918 CP 10 Jump forward with report numbers '0 to 9'.
04920 JR C,MAIN_5
04922 ADD A,7 Add the ASCII letter offset value.
MAIN_5 04924 CALL OUT_CODE Print the report code and follow it with a 'space'.
04927 LD A," "
04929 RST 16
04930 LD A,B Fetch the report value (used to identify the required report message).
04931 LD DE,5009 Print the message.
04934 CALL PO_MSG
04937 XOR A Follow it by a 'comma' and a 'space'.
04938 LD DE,5430
04941 CALL PO_MSG
04944 LD BC,(23621) Now fetch the current line number (PPC) and print it as well.
04948 CALL OUT_NUM_1
04951 LD A,":" Follow it by a ':'.
04953 RST 16
04954 LD C,(IY+13) Fetch the current statement number (SUBPPC) into the BC register pair and print it.
04957 LD B,0
04959 CALL OUT_NUM_1
04962 CALL CLEAR_SP Clear the editing area.
04965 LD A,(23610) Fetch the error number (ERR-NR) again.
04968 INC A Increment it as usual.
04969 JR Z,MAIN_9 If the program was completed successfully there cannot be any 'CONTinuing' so jump.
04971 CP 9 If the program halted with 'STOP statement' or 'BREAK into program' CONTinuing will be from the next statement; otherwise SUBPPC is unchanged.
04973 JR Z,MAIN_6
04975 CP 21
04977 JR NZ,MAIN_7
MAIN_6 04979 INC (IY+13)
MAIN_7 04982 LD BC,3 The system variables OLDPPC and OSPCC have now to be made to hold the CONTinuing line and statement numbers.
04985 LD DE,23664
04988 LD HL,23620 The values used will be those in PPC and SUBPPC unless NSPPC indicates that the 'break' occurred before a 'jump' (i.e. after a GO TO statement etc.).
04991 BIT 7,(HL)
04993 JR Z,MAIN_8
04995 ADD HL,BC
MAIN_8 04996 LDDR
MAIN_9 04998 LD (IY+10),255 NSPPC is reset to indicate 'no jump'.
05002 RES 3,(IY+1) 'K mode' is selected (reset bit 3 of FLAGS).
05006 JP MAIN_2 And finally the jump back is made but no program listing will appear until requested.
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