The BBC and Master Computer Public Domain Library
9646 TRACE
Submitted by Steve Fewell
Description:
Call routine &9B1E to check if there is a tokenised Line Number following the TRACE Keyword. If a Line Number is
found then detokenise the Line Number and set the IWA to the Line Number value.
-
If the carry flag is not set, then a Line Number was not found and A contains the character after the TRACE Keyword, so:
- * If A is the 'ON-Token' [#&EE] then jump to the TRACE ON routine at &9667
- * If A is the 'OFF-Token' [#&87] then jump to the TRACE OFF routine at &9670
- * Otherwise, the TRACE Line Number must be a variable/expression, so call routine &926F to evaluate
- the variable/expression, convert the result to Integer and store the result in the IWA
- * If A is the 'OFF-Token' [#&87] then jump to the TRACE OFF routine at &9670
issuing 'Syntax error' if it doesn't.
Set the TRACE Line Number (locations &21-&22) to the 16-bit Line Number from the IWA (locations &2A-&2B).
Set the TRACE flag (location &20) to #&FF to indicate that TRACEing is currently activated.
Jump to &9005 to continue executing the next statement of the Program.
[&9667] TRACE ON routine
Increment the BASIC Text Pointer A offset (&0A) to skip over the ON-Token.
Call routine &9BA6 to check that the statement terminates correctly with a ':', '<cr>' or 'ELSE-token' character,
issuing 'Syntax error' if it doesn't.
Set A to #&FF.
-
Jump to &965F to:
- * Set the TRACE Line Number MSB (location &22) to A (#&FF) to indicate that there is no maximum
- TRACE Line Number.
- * Set the TRACE flag (location &20) to #&FF to indicate that TRACEing is currently activated.
- * Jump to &9005 to continue executing the next statement of the Program.
- TRACE Line Number.
[&9670] TRACE OFF routine
Increment the BASIC Text Pointer A offset (&0A) to skip over the OFF-Token.
Call routine &9BA6 to check that the statement terminates correctly with a ':', '<cr>' or 'ELSE-token' character,
issuing 'Syntax error' if it doesn't.
Set A to #&00.
-
Jump to &9663 to:
- * Set the TRACE flag (location &20) to A (#&00) to indicate that TRACEing is NOT currently activated.
- * Jump to &9005 to continue executing the next statement of the Program.
- * Jump to &9005 to continue executing the next statement of the Program.
Disassembly for the TRACE routine
| 9646 | 032 030 155 | 20 1E 9B | JSR &9B1E Detokenise the Line Number at PTR A & Set IWA to the Line Number value | |
| 9649 | 176 011 | B0 0B | BCS 11 --> &9656 | |
| 964B | 201 238 | C9 EE | CMP#&EE | |
| 964D | 240 024 | F0 18 | BEQ 24 --> &9667 TRACE ON | |
| 964F | 201 135 | C9 87 | CMP#&87 | |
| 9651 | 240 029 | F0 1D | BEQ 29 --> &9670 TRACE OFF | |
| 9653 | o | 032 111 146 | 20 6F 92 | JSR &926F Evaluate Expression at BASIC Text pointer A convert result to integer |
| 9656 | 032 166 155 | 20 A6 9B | JSR &9BA6 Check end of Statement | |
| 9659 | * | 165 042 | A5 2A | LDA &2A |
| 965B | ! | 133 033 | 85 21 | STA &21 |
| 965D | + | 165 043 | A5 2B | LDA &2B |
| 965F | " | 133 034 | 85 22 | STA &22 |
| 9661 | 169 255 | A9 FF | LDA#&FF | |
| 9663 | 133 032 | 85 20 | STA &20 | |
| 9665 | 128 212 | 80 D4 | BRA -44 --> &963B [JMP &9005] Process the next statement | |
| 9667 | 230 010 | E6 0A | INC &0A | |
| 9669 | 032 166 155 | 20 A6 9B | JSR &9BA6 Check end of Statement | |
| 966C | 169 255 | A9 FF | LDA#&FF | |
| 966E | 208 239 | D0 EF | BNE -17 --> &965F | |
| 9670 | 230 010 | E6 0A | INC &0A | |
| 9672 | 032 166 155 | 20 A6 9B | JSR &9BA6 Check end of Statement | |
| 9675 | 169 000 | A9 00 | LDA#&00 | |
| 9677 | 128 234 | 80 EA | BRA -22 --> &9663 |
