TextStar - Revision history

99.6.119.22: /* Relax and Unwind */

2009-11-11T02:20:07Z

Relax and Unwind

← Older revision		Revision as of 19:20, 10 November 2009
Line 145:		Line 145:
	=== Relax and Unwind ===		=== Relax and Unwind ===

	<div style="border: 3px red solid;padding: 1em; background-color:lightyellow">		Now that we can get a peek at a keystroke before ''TEXT'' does, what next?

			Other programs use the ''CHGET'' routine too. So we have to make sure that ''CHGET'' was invoked by ''TEXT'' and not another program. ''TEXT'' calls ''CHGET'' at address 5FEDH. (Actually it's called at 63F1H, from within a routine called by 5FEDH.) This means that there will be a ''RET''urn to 5FF0H somewhere on the stack.

			When we get control via the FADEH RAM hook, the return address to ''TEXT'', if it was called by ''TEXT'', is 10 levels (20 bytes) down in the stack.

			So we have to unwind the stack 10 levels and see if the address 5FF0H is there. If it is, then ''CHGET'' was called from ''TEXT'' and this keystroke is for us. If not, then we must put everything back the way it was.

			<div style="border: 3px red solid;padding: 1em; background-color:lightyellow; margin: auto 3em auto 3em">
	<p>		<p>
	This discussion is included for hysterical reasons; the program as it		This discussion is included for hysterical reasons; the program as it
Line 181:		Line 189:
	</div>		</div>

	~~Now that we can get a peek at a keystroke before ''TEXT'' does, what next?~~

	Other programs use the ''CHGET'' routine too. So we have to make sure that ''CHGET'' was invoked by ''TEXT'' and not another program. ''TEXT'' calls ''CHGET'' at address 5FEDH. (Actually it's called at 63F1H, from within a routine called by 5FEDH.) This means that there will be a ''RET''urn to 5FF0H somewhere on the stack.

	~~When we get control via the FADEH RAM hook, the return address to ''TEXT'', if it was called by ''TEXT'', is 10 levels (20 bytes) down in the stack.~~

	So we have to unwind the stack 10 levels and see if the address 5FF0H is there. If it is, then ''CHGET'' was called from ''TEXT'' and this keystroke is for us. If not, then we must put everything back the way it was.

	How can a kestroke in ''TEXT'' not be for us? There are functions within ''TEXT'', such as ''F1'' (''Find'') function, that require keyboard input separate form the main ''TEXT'' processing loop.		How can a kestroke in ''TEXT'' not be for us? There are functions within ''TEXT'', such as ''F1'' (''Find'') function, that require keyboard input separate form the main ''TEXT'' processing loop.

99.6.119.22: /* Relax and Unwind */

2009-11-11T02:14:22Z

Relax and Unwind

← Older revision		Revision as of 19:14, 10 November 2009
Line 145:		Line 145:
	=== Relax and Unwind ===		=== Relax and Unwind ===

	<div style="border: 3px red solid;padding: 1em">		<div style="border: 3px red solid;padding: 1em; background-color:lightyellow">
	<p>		<p>
	This discussion is included for hysterical reasons; the program as it		This discussion is included for hysterical reasons; the program as it
Line 154:		Line 154:
	The problem with the approach in the original TextStar was that it		The problem with the approach in the original TextStar was that it
	"dropped" bytes from the stack and added them back in. This is a no-no.		"dropped" bytes from the stack and added them back in. This is a no-no.
	Anything below the stack pointer is free space, ~~and so~~ it is not		Anything below the stack pointer is free space. Increasing the pointer value
			(since the stack grows downward in RAM) effectively "deallocates"
			the memory below the new pointer location. If a call is made, or an interrupt
			occurs during this time, the free space will likely be overwritten.
			So, it is not
	safe to assume that the data will be there when you lower the stack pointer		safe to assume that the data will be there when you lower the stack pointer
	position to include them again.		position to include them again.
Line 160:		Line 164:

	<p>		<p>
	I believe Stan was assuming that his "disable interrupts" instruction		I believe Stan was assuming that his ''DI'' (''disable interrupts'') instruction
	would be sufficient to prevent the temporarily dropped bytes from being		would be sufficient to prevent the temporarily dropped bytes from being
	corrupted; however, the TRAP non-maskable interrupt is not prevented		corrupted; however, the TRAP non-maskable interrupt is not prevented
Line 169:		Line 173:
	to observe and modify the 5FF0 pointer on the stack without		to observe and modify the 5FF0 pointer on the stack without
	the dangerous and unnecessary step of unwinding. The enable and disable		the dangerous and unnecessary step of unwinding. The enable and disable
	interrupt instructions were unnecessary and removed. Finally, ~~the other~~ registers ~~were~~ preserved (and restored) since it wasn't ~~clear~~ to me		interrupt instructions were unnecessary and removed. Finally, additional registers (HL and PSW) are now preserved (and restored) since it wasn't obvious to me that it was safe to destroy them.
	that it was safe to destroy them.
	</p>		</p>

99.6.119.22: /* Relax and Unwind */

2009-11-11T02:06:24Z

Relax and Unwind

← Older revision		Revision as of 19:06, 10 November 2009
Line 145:		Line 145:
	=== Relax and Unwind ===		=== Relax and Unwind ===

	<div style="border: 3px red solid">		<div style="border: 3px red solid;padding: 1em">
	<p>		<p>
	This discussion is included for hysterical reasons; the program as it		This discussion is included for hysterical reasons; the program as it
Line 174:		Line 174:

	<p>		<p>
	-- John		-- John (jhoger@pobox.com)
	</p>		</p>
	</div>		</div>

99.6.119.22: /* Relax and Unwind */

2009-11-11T00:58:48Z

Relax and Unwind

← Older revision		Revision as of 17:58, 10 November 2009
Line 144:		Line 144:

	=== Relax and Unwind ===		=== Relax and Unwind ===

			<div style="border: 3px red solid">
			<p>
			This discussion is included for hysterical reasons; the program as it
			currently exists no longer unwinds the stack.
			</p>

			<p>
			The problem with the approach in the original TextStar was that it
			"dropped" bytes from the stack and added them back in. This is a no-no.
			Anything below the stack pointer is free space, and so it is not
			safe to assume that the data will be there when you lower the stack pointer
			position to include them again.
			</p>

			<p>
			I believe Stan was assuming that his "disable interrupts" instruction
			would be sufficient to prevent the temporarily dropped bytes from being
			corrupted; however, the TRAP non-maskable interrupt is not prevented
			by DI. The result, I believe, was that power-off was causing the stack to get corrupted.
			</p>
			<p>
			The unwind code has been replaced with logic that leverages the DESP instruction
			to observe and modify the 5FF0 pointer on the stack without
			the dangerous and unnecessary step of unwinding. The enable and disable
			interrupt instructions were unnecessary and removed. Finally, the other registers were preserved (and restored) since it wasn't clear to me
			that it was safe to destroy them.
			</p>

			<p>
			-- John
			</p>
			</div>

	Now that we can get a peek at a keystroke before ''TEXT'' does, what next?		Now that we can get a peek at a keystroke before ''TEXT'' does, what next?

Jhoger at 19:51, 10 November 2009

2009-11-10T19:51:19Z

← Older revision		Revision as of 12:51, 10 November 2009
Line 54:		Line 54:
	\|-		\|-
	\| ^T \|\| Delete word		\| ^T \|\| Delete word
			\|-
			\| ^BKSP \|\| Delete prior word (NEW feature -- [[User:Jhoger\|Jhoger]])
	\|-		\|-
	\| ^Y \|\| Delete line		\| ^Y \|\| Delete line

Jhoger: TEXTSTAR moved to TextStar

2009-11-10T19:48:40Z

TEXTSTAR moved to TextStar

← Older revision	Revision as of 12:48, 10 November 2009
(No difference)

99.6.119.22: /* A Diamond in the Rough */

2009-11-10T01:33:10Z

A Diamond in the Rough

← Older revision		Revision as of 18:33, 9 November 2009
Line 24:		Line 24:

	A simple change to ''TextStar'' could have made it ignore the ''TEXT'' control keys, but I felt it would be better to leave them in. The program owes its small size (381 bytes) to its method; it traps keyboard input and translates only ''WordStar'' control codes into their ''TEXT'' equivalents, passing all other keystrokes directly to ''TEXT'' for normal processing.		A simple change to ''TextStar'' could have made it ignore the ''TEXT'' control keys, but I felt it would be better to leave them in. The program owes its small size (381 bytes) to its method; it traps keyboard input and translates only ''WordStar'' control codes into their ''TEXT'' equivalents, passing all other keystrokes directly to ''TEXT'' for normal processing.

			<div style="border: 3px darkgray solid; margin: auto 2in auto 2in">

	{\| style="margin: 1em auto 1em auto;border:1px solid darkgray"		{\| style="margin: 1em auto 1em auto;border:1px solid darkgray"
Line 68:		Line 70:
	\| ^QY \|\| Delete to end of line		\| ^QY \|\| Delete to end of line
	\|}		\|}

			</div>

	== Vive La Difference ==		== Vive La Difference ==

99.6.119.22: /* A Diamond in the Rough */

2009-11-10T01:27:22Z

A Diamond in the Rough

@@ Line 45: / Line 45: @@
 | ^QR || Top of file
 |-
 |}

99.6.119.22: /* A Diamond in the Rough */

2009-11-10T01:12:59Z

A Diamond in the Rough

← Older revision		Revision as of 18:12, 9 November 2009
Line 24:		Line 24:

	A simple change to ''TextStar'' could have made it ignore the ''TEXT'' control keys, but I felt it would be better to leave them in. The program owes its small size (381 bytes) to its method; it traps keyboard input and translates only ''WordStar'' control codes into their ''TEXT'' equivalents, passing all other keystrokes directly to ''TEXT'' for normal processing.		A simple change to ''TextStar'' could have made it ignore the ''TEXT'' control keys, but I felt it would be better to leave them in. The program owes its small size (381 bytes) to its method; it traps keyboard input and translates only ''WordStar'' control codes into their ''TEXT'' equivalents, passing all other keystrokes directly to ''TEXT'' for normal processing.

			{\| style="margin: 1em auto 1em auto;border:1px solid darkgray"
			\|+ '''Cursor Movement'''
			\| ^D \|\| Right one character
			\|- <bl/>
			\| ^F \|\| Right one word
			\|-
			\| ^QD \|\| Right to end of current line
			\|-
			\| ^S \|\| Left one character
			\|-
			\| ^A \|\| Left one word
			\|-
			\| ^QS \|\| Left to beginning of current line
			\|-
			\| ^E \|\| Up one line
			\|-
			\| ^QE \|\| Top of screen, column 1
			\|-
			\| ^QR \|\| Top of file
			\|-
			\|}

	== Vive La Difference ==		== Vive La Difference ==

99.6.119.22 at 21:07, 9 November 2009

2009-11-09T21:07:03Z

← Older revision		Revision as of 14:07, 9 November 2009
Line 123:		Line 123:
	On a ''^KD'' ( or ''F8'') exit command, we must restore RAM hooks to their original values and exit to the main menu by ''JMP''ing to location 5797H. Failure to do so may result in a machine that feels very cool to the touch (i.e., COLD START!).		On a ''^KD'' ( or ''F8'') exit command, we must restore RAM hooks to their original values and exit to the main menu by ''JMP''ing to location 5797H. Failure to do so may result in a machine that feels very cool to the touch (i.e., COLD START!).

	~~(IN PROGRESS)~~		[[Category:Model 100 Classics]]