Difference between revisions of "Passing a parameter to a language"
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the language is running it is running in the language memory and | the language is running it is running in the language memory and | ||
can no longer see the command that was used to start it as that | can no longer see the command that was used to start it as that | ||
| − | will | + | will by neccessity be in the I/O memory. |
Language code can examine the I/O memory with [[OSWORD 5]] and extract | Language code can examine the I/O memory with [[OSWORD 5]] and extract | ||
a command line. EDIT on the Master does this so you can start EDIT | a command line. EDIT on the Master does this so you can start EDIT | ||
specifying a file to load. Of course, this is not possible if the | specifying a file to load. Of course, this is not possible if the | ||
| − | language was started | + | language was started with [[OSBYTE &8E|OSBYTE 142]] as there is no |
command line. Note that this cannot be done via the [[OSARGS]] call | command line. Note that this cannot be done via the [[OSARGS]] call | ||
to read the command line parameters, as that points to the command | to read the command line parameters, as that points to the command | ||
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command already in local memory and with a register pointing to | command already in local memory and with a register pointing to | ||
it, or an API call to fetch it: | it, or an API call to fetch it: | ||
| − | * 6809: X=>command line parameters | + | * 6809: X=>command line parameters |
* PDP11: R1=>command line parameters | * PDP11: R1=>command line parameters | ||
| − | * ARM: OS_GetEnv gets command line parameter address | + | * ARM: OS_GetEnv gets command line parameter address |
== See Also == | == See Also == | ||
* [[Returning exit code]] | * [[Returning exit code]] | ||
[[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 01:09, 1 July 2018 (CEST) | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 01:09, 1 July 2018 (CEST) | ||
Latest revision as of 23:43, 3 April 2020
When a language is entered it is just entered at the language entry point. On the 6502 there is no mechanism to pass a parameter to the language, it is entered as a straight jump of a selected ROM. Once the language is running it is running in the language memory and can no longer see the command that was used to start it as that will by neccessity be in the I/O memory.
Language code can examine the I/O memory with OSWORD 5 and extract a command line. EDIT on the Master does this so you can start EDIT specifying a file to load. Of course, this is not possible if the language was started with OSBYTE 142 as there is no command line. Note that this cannot be done via the OSARGS call to read the command line parameters, as that points to the command line used to run a program from a file, not to the command line used to execute a ROM command.
If the parameter you want to pass to your language is a simple 8-bit byte than it can by passed via the OSBYTE 1 user/return byte. Your *command writes its data to OSBYTE 1, then starts up the language. The language then reads the OSBYTE 1 value to collect the parameter.
.L8000:JMP Language .L8003:JMP Service ... .Service4 \ Eventually gets to... .mycommand JSR ParseNumber :\ Parse 8-bit parameter to A TAX:LDA #1:JSR OSBYTE :\ Set user/return code LDX &F4 :\ X=my ROM number LDA #142:JMP OSBYTE :\ Enter me as a language ... .Language LDX #&FF:TXS:CLI :\ Standard language startup LDX #0:LDA #1:JSR OSBYTE :\ Read user/return code \ X now has the parameter you used with your *command
Other processors
Some non-6502 processors enter language code with the selection command already in local memory and with a register pointing to it, or an API call to fetch it:
- 6809: X=>command line parameters
- PDP11: R1=>command line parameters
- ARM: OS_GetEnv gets command line parameter address
