Running BASIC Code from OptROM - Revision history

99.6.119.22 at 05:24, 19 May 2009

2009-05-19T05:24:13Z

← Older revision		Revision as of 22:24, 18 May 2009
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	</pre></code>		</pre></code>

	[[Category:Model T Developer Reference]]		[[Category:Model T Developer Reference]] [[Category:Option ROM]]

124.157.105.102: /* How the BASIC Interpreter Works */

2009-05-02T04:58:48Z

How the BASIC Interpreter Works

← Older revision		Revision as of 21:58, 1 May 2009
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	== How the BASIC Interpreter Works ==		== How the BASIC Interpreter Works ==

	This disassembly of the Altair BASIC interpreter, though not the same code, should shed some light since it is so well commented (~~Phil~~ Avery hipped me to this resource):		This disassembly of the Altair BASIC interpreter, though not the same code, should shed some light since it is so well commented (Philip Avery hipped me to this resource):

	[http://www.interact-sw.co.uk/altair/index2.html Altair BASIC Walk-Through]		[http://www.interact-sw.co.uk/altair/index2.html Altair BASIC Walk-Through]

Jhoger at 06:57, 31 January 2009

2009-01-31T06:57:43Z

← Older revision		Revision as of 23:57, 30 January 2009
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	0871H (C9H) RET		0871H (C9H) RET
	</pre></code>		</pre></code>

			[[Category:Model T Developer Reference]]

Jhoger: /* Thoughts from Ken Pettit */

2008-06-02T00:51:35Z

Thoughts from Ken Pettit

← Older revision		Revision as of 17:51, 1 June 2008
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	== Thoughts from Ken Pettit ==		== Thoughts from Ken Pettit ==

	I have looked a the BASIC interpreter quite a bit. The main program execution loop (for M100) is at address 0804h. The first few function calls perform things like checking for ON COM, ON TIME, CTRL-BREAK, etc. The middle part executes the next instruction, and the last part steps forward to the next instruction / line #. This routine would have to be rewritten to run in RAM and fetch BASIC lines from OptROM. Additionally, the routine below it would have to be rewritten too - it pushes the 0804h return address on the stack that most BASIC instructions use by doing a simple "RET' . This would have to push the address of the re-written RAM based loop.		I have looked at the BASIC interpreter quite a bit. The main program execution loop (for M100) is at address 0804h. The first few function calls perform things like checking for ON COM, ON TIME, CTRL-BREAK, etc. The middle part executes the next instruction, and the last part steps forward to the next instruction / line #. This routine would have to be rewritten to run in RAM and fetch BASIC lines from OptROM. Additionally, the routine below it would have to be rewritten too - it pushes the 0804h return address on the stack that most BASIC instructions use by doing a simple "RET' . This would have to push the address of the re-written RAM based loop.

	The problem areas will be in handling the ON TIME, ON COM, ON KEY, and STOP (CTRL-BREAK uses the STOP instruction). From what I remember, these perform an absolute "JMP" into the ROM which then lead back to the 0804h loop and/or search for line numbered BASIC lines in RAM.		The problem areas will be in handling the ON TIME, ON COM, ON KEY, and STOP (CTRL-BREAK uses the STOP instruction). From what I remember, these perform an absolute "JMP" into the ROM which then lead back to the 0804h loop and/or search for line numbered BASIC lines in RAM.

Jhoger: /* How the BASIC Interpreter Works */

2008-06-02T00:51:19Z

How the BASIC Interpreter Works

← Older revision		Revision as of 17:51, 1 June 2008
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	[http://www.interact-sw.co.uk/altair/index2.html Altair BASIC Walk-Through]		[http://www.interact-sw.co.uk/altair/index2.html Altair BASIC Walk-Through]

	In particular, ~~not~~ the "Execution" section 1.9 which is relevant to this problem.		In particular, note the "Execution" section 1.9 which is relevant to this problem.

	== Running BASIC Programs: Excerpt from Hidden Powers (Chris Morgan) ==		== Running BASIC Programs: Excerpt from Hidden Powers (Chris Morgan) ==

64.81.88.222: /* Running BASIC Programs: Excerpt from Hidden Powers of the TRS-80 Model 100 (Chris Morgan) */

2008-02-23T07:11:06Z

Running BASIC Programs: Excerpt from Hidden Powers of the TRS-80 Model 100 (Chris Morgan)

← Older revision		Revision as of 00:11, 23 February 2008
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	In particular, not the "Execution" section 1.9 which is relevant to this problem.		In particular, not the "Execution" section 1.9 which is relevant to this problem.

	== Running BASIC Programs: Excerpt from Hidden Powers ~~of the TRS-80 Model 100~~ (Chris Morgan) ==		== Running BASIC Programs: Excerpt from Hidden Powers (Chris Morgan) ==

	The next major area of memory contains the code that runs BASIC programs.		The next major area of memory contains the code that runs BASIC programs.
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	as is used by the RST 2 routine to check for numbers and skip over		as is used by the RST 2 routine to check for numbers and skip over
	spaces.		spaces.


	== Commented M100 "Inner Interpreter" Code ==		== Commented M100 "Inner Interpreter" Code ==

64.81.88.222: /* Callers of BASIC Inner Interpreter */

2008-02-23T07:10:09Z

Callers of BASIC Inner Interpreter

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	CLOAD, CLOADM, CLEAR, NEXT, Input Routine, Various places in Menu.		CLOAD, CLOADM, CLEAR, NEXT, Input Routine, Various places in Menu.

	~~This raises the issue of whether we can run this loop from RAM.~~

	== How the BASIC Interpreter Works ==		== How the BASIC Interpreter Works ==

64.81.88.222: /* Thoughts from Ken Pettit */

2008-02-23T07:09:24Z

Thoughts from Ken Pettit

← Older revision		Revision as of 00:09, 23 February 2008
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	The problem areas will be in handling the ON TIME, ON COM, ON KEY, and STOP (CTRL-BREAK uses the STOP instruction). From what I remember, these perform an absolute "JMP" into the ROM which then lead back to the 0804h loop and/or search for line numbered BASIC lines in RAM.		The problem areas will be in handling the ON TIME, ON COM, ON KEY, and STOP (CTRL-BREAK uses the STOP instruction). From what I remember, these perform an absolute "JMP" into the ROM which then lead back to the 0804h loop and/or search for line numbered BASIC lines in RAM.

			Seems like GOTO and DATA/RESTORE/READ statements may be a problem too (BASIC commands that "lookup" line numbers). You might find that several functions need to be re-implemented in the OptROM and ran from there, then switch to the main ROM to run the rest.

	== Callers of BASIC Inner Interpreter ==		== Callers of BASIC Inner Interpreter ==

64.81.88.222: /* Short Conversation from M100SIG */

2008-02-23T01:03:02Z

Short Conversation from M100SIG

← Older revision		Revision as of 18:03, 22 February 2008
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	A small program could switch to the OptROM, read a BASIC line (tokenized)		A small program could switch to the OptROM, read a BASIC line (tokenized)
	into RAM, switch back to system ROM, and then feed it to the interpreter loop.		into RAM, switch back to system ROM, and then feed it to the interpreter loop.
	There is no housekeeping since BASIC takes care of it. ~~Oops, I forgot, as part~~		There is no housekeeping since BASIC takes care of it.
	~~of each line I believe that there is also the address of~~ the next statement.		The pointer to the next statement
	~~That~~ needs to be fixed up also. Anyway, it's a fairly starightforward		needs to be fixed up also. Anyway, it's a fairly starightforward
	proposition. If there is any interest I can dive back into my notes and		proposition. If there is any interest I can dive back into my notes and
	re-figure out what's what (in any case I got all my info from Robert		re-figure out what's what (in any case I got all my info from Robert

64.81.88.222: /* Short Conversation from M100SIG */

2008-02-23T00:58:09Z

Short Conversation from M100SIG

← Older revision		Revision as of 17:58, 22 February 2008
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	moves but there is a ROM call that interprets each tokenized statement. Other		moves but there is a ROM call that interprets each tokenized statement. Other
	ROM routines find the next statement to execute. Its been a while but my		ROM routines find the next statement to execute. Its been a while but my
	memory is sort of dim on the subject but each BASIC ~~statement~~ in storage is		memory is sort of dim on the subject but each BASIC line in storage is
	prefixed with the line line followed by the statement tokens followed by a		prefixed with the next line pointer and the line number. followed by the statement tokens followed by a
	null. Three nulls indicate the end of the program (end-of-statement null		null. Three nulls indicate the end of the program (end-of-statement null
	followed by a line number of zero).		followed by a line number of zero).