The BBC and Master Computer Public Domain Library
9048 Prompt for command line and execute the entered command(s)
Submitted by Steve Fewell
Description:
If called from &9048 then a full initialisation will be done before the command line prompt appears.
-
This will reset the following:
- * Program start address
- * Stack Pointer
- * Clear *EDIT mode
- * REPEAT/FOR/GOSUB parameters, return addresses, etc...
- * Page &7 user tables (&07F0-&07FF)
- * Variable pointer tables (destroys all variables that have been created)
- * Stack Pointer
Reset the BASIC Text pointer A (&0B, &0C) to &0700 (the address of the command line buffer).
Call routine &B2E0 to reset the 'ON ERROR' pointer to BASIC's default error handling routine.
Call OSWRCH with A = #&3E to output the '>' [prompt character] to the screen.
Call routine &BAA4 to read the input line (using OSWORD 0) and store the input to the command line buffer (&0700-
&07EF). The parameters (line length, minimum and maximum acceptable characters, etc...) for this input as the same as
those used during the INPUT command (as both inputs are done by the same routine, (&BA70)).
[&905C] Set the 6502 stack pointer to #&FF (to clear any FN/PROC subroutines that were in progress when the last
command (that was executed by the BASIC Intrepreter) had finished, or when the last program execution had ended).
Call routine &B2E0 (again) to reset the 'ON ERROR' pointer to BASIC's default error handling routine.
Call routine &BB1B to tokenise the command line (&0700-&07EF) and to enter the line into the current BASIC
program if a line number was supplied at the start of the command line.
If the Command line contained a program line (which has now been inserted into the current program), then jump back
to &9048 to do a full initialisation (as after a line in the Program has been inserted/changed or removed, any defined
variables need to be reset, because the TOP of the program has now been changed - corrupting the variable storage space).
Otherwise, if a direct command (not a program line) has been entered, then call &901E to execute the statement(s) on
the Command Line.
Disassembly for the Prompt for command line and execute the entered command(s) routine
|
032 220 187 |
20 DC BB |
JSR &BBDC Initialise Page 7 & reset Variable pointers, etc... | |
|
160 007 |
A0 07 |
LDY#&07 |
|
904D |
|
132 012 |
84 0C |
STY &0C |
904F |
d |
100 011 |
64 0B |
STZ &0B |
9051 |
|
032 224 178 |
20 E0 B2 |
JSR &B2E0 Reset 'ON ERROR' pointer to BASIC's default error handling routine |
9054 |
> |
169 062 |
A9 3E |
LDA#&3E |
9056 |
|
032 238 255 |
20 EE FF |
JSR &FFEE OSWRCH |
9059 |
|
032 164 186 |
20 A4 BA |
JSR &BAA4 Prompt for & get the User's input line (storing it in buffer &0700-&07FF) |
| 905C |
|
162 255 |
A2 FF |
LDX#&FF |
905E |
|
154 |
9A |
TXS |
905F |
|
032 224 178 |
20 E0 B2 |
JSR &B2E0 Reset 'ON ERROR' pointer to BASIC's default error handling routine |
9062 |
|
032 027 187 |
20 1B BB |
JSR &BB1B Tokenise Command Line and Insert Line into Program (if line number given) |
9065 |
|
176 225 |
B0 E1 |
BCS -31 --> &9048 Initialise & prompt for next command line |
9067 |
z |
128 122 |
80 7A |
BRA 122 --> &90E3 Execute the command line |
