Update hbios.asm

Minor cosmetic changes.

Source/HBIOS/hbios.asm

@@ -250,7 +250,7 @@ CB_BIDROMDN	.DB	BID_ROMDN
 ;
 ; DEFINITIONS
 ;
-HBX_BUFSIZ	.EQU	$40		; INTERBANK COPY BUFFER SIZE
+HBX_BUFSIZ	.EQU	$40		; INTERBANK COPY BOUNCE BUFFER SIZE
 ;
 ; HBIOS IDENTIFICATION DATA BLOCK
 ;
@@ -263,19 +263,25 @@ HBX_IDENT:
 ;   HBIOS ENTRY FOR RST 08 PROCESSING
 ;==================================================================================================
 ;
+; NOTE: THE SIZE OF HBX_TMPSTK (TYPICALLY 20 BYTES) IS INSUFFICIENT FOR
+; FREERTOS IF AN INTERRUPT STRIKES WHILE THE TEMPORARY STACK IS ACTIVE.
+; BELOW, HBX_BUF HAS BEEN USURPED TO PROVIDE A LARGER TEMP STACK TO
+; ACCOMMODATE FREERTOS.  HBX_BUF IS ONLY USED AS A BOUNCE BUFFER, SO IT'S
+; USE WILL NEVER OVERLAP WITH BELOW.
+;
 HBX_INVOKE:
 	LD	(HBX_INVSP),SP		; SAVE ORIGINAL STACK FRAME
 	LD	A,(HB_CURBNK)		; GET CURRENT BANK
 	LD	(HB_INVBNK),A		; SAVE INVOCATION BANK
 
-	LD	SP,HBX_TMPSTK		; BORROW HBX_BUF FOR STACK IN HIGH MEMORY
+	LD	SP,HBX_BUF_END		; BORROW HBX_BUF FOR TEMP STACK
 	LD	A,BID_BIOS		; HBIOS BANK
 	CALL	HBX_BNKSEL		; SELECT IT
 	LD	SP,HB_STACK		; NOW USE FULL HBIOS STACK IN HBIOS BANK
 
 	CALL	HB_DISPATCH		; CALL HBIOS FUNCTION DISPATCHER
 
-	LD	SP,HBX_TMPSTK		; BORROW HBX_BUF FOR STACK IN HIGH MEMORY
+	LD	SP,HBX_BUF_END		; BORROW HBX_BUF FOR TEMP STACK
 	PUSH	AF			; SAVE AF (FUNCTION RETURN)
 
 	LD	A,(HB_INVBNK)		; LOAD ORIGINAL BANK
@@ -376,7 +382,6 @@ HBX_BNKSEL1:
 ;::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
 ; Copy Data - Possibly between banks.  This resembles CP/M 3, but
 ;  usage of the HL and DE registers is reversed.
-; Caller MUST ensure stack is already in high memory.
 ; Caller MUST preset HBX_SRCBNK and HBX_DSTBNK.
 ; Caller MUST disable ints if IM1 active
 ; Enter:
@@ -390,7 +395,7 @@ HBX_BNKSEL1:
 ;
 HBX_BNKCPY:
 	LD	(HBX_BC_SP),SP		; PUT STACK
-	LD	SP,HBX_BNKSTK		; TEMPORARY STACK IN HIGH MEMORY (NOT IN HBX_BUF)
+	LD	SP,HBX_TMPSTK		; ... IN HI MEM
 
 	LD	A,(HB_CURBNK)		; GET CURRENT BANK
 	PUSH	AF			; AND SAVE TO RESTORE LATER
@@ -471,7 +476,7 @@ HBX_TGTADR	.EQU	$ + 1
 ;
 HBX_PEEK:
 	LD	(HBX_PPSP),SP		; SAVE ORIGINAL STACK FRAME
-	LD	SP,HBX_TMPSTK		; BORROW HBX_BUF FOR STACK IN HIGH MEMORY
+	LD	SP,HBX_TMPSTK		; USE SMALL TEMP STACK FRAME IN HI MEM
 	LD	A,(HB_CURBNK)
 	PUSH	AF
 	LD	A,D
@@ -481,7 +486,7 @@ HBX_PEEK:
 ;
 HBX_POKE:
 	LD	(HBX_PPSP),SP		; SAVE ORIGINAL STACK FRAME
-	LD	SP,HBX_TMPSTK		; BORROW HBX_BUF FOR STACK IN HIGH MEMORY
+	LD	SP,HBX_TMPSTK		; USE SMALL TEMP STACK FRAME IN HI MEM
 	LD	A,(HB_CURBNK)
 	PUSH	AF
 	LD	A,D
@@ -498,12 +503,12 @@ HBX_PPSP	.EQU	$ - 2
 ; PRIVATE STACK AT END OF HBIOS CODE
 ; OCCUPIES SPACE BEFORE IVT
 ;
-HBX_STKSIZ	.EQU	$FF00 - $
-		.ECHO	"HBIOS PROXY STACK space: "
-		.ECHO	HBX_STKSIZ
+HBX_INTSTKSIZ	.EQU	$FF00 - $
+		.ECHO	"HBIOS INT STACK space: "
+		.ECHO	HBX_INTSTKSIZ
 		.ECHO	" bytes.\n"
-		.FILL	HBX_STKSIZ,$FF
-HBX_STACK	.EQU	$
+		.FILL	HBX_INTSTKSIZ,$FF
+HBX_INTSTK	.EQU	$
 ;
 #IF (INTMODE == 2)
 ;
@@ -585,7 +590,7 @@ HBX_INT:	; COMMON INTERRUPT ROUTING CODE
 	EX	(SP),HL			; SAVE HL AND GET INT JP TABLE OFFSET
 
 	LD	(HBX_INT_SP),SP		; SAVE ORIGINAL STACK FRAME
-	LD	SP,HBX_STACK		; USE STACK FRAME IN HI MEM
+	LD	SP,HBX_INTSTK		; USE DEDICATED INT STACK FRAME IN HI MEM
 
 	; SAVE STATE (HL SAVED PREVIOUSLY ON ORIGINAL STACK FRAME)
 	PUSH	AF			; SAVE AF
@@ -620,25 +625,23 @@ HBX_INT_SP	.EQU	$ - 2
 ;
 #ENDIF
 ;
-; FILL TO START OF BOUNCE BUFFER
+; SMALL TEMPORARY STACK FOR USE BY BNKCPY, PEEK, AND POKE
 ;
-HBX_PROXYFILL	.EQU	(HBX_XFC - HBX_BUFSIZ - $)
-		.ECHO	"HBIOS PROXY space remaining: "
-		.ECHO	HBX_PROXYFILL
+HBX_TMPSTKSIZ	.EQU	(HBX_XFC - HBX_BUFSIZ - $)
+		.ECHO	"HBIOS TEMP STACK space: "
+		.ECHO	HBX_TMPSTKSIZ
 		.ECHO	" bytes.\n"
-		.FILL	HBX_PROXYFILL,$FF
-;
-; TEMPORARY STACK FOR USE BY HBX_BNKCPY (NOT IN HBX_BUF)
+		.FILL	HBX_TMPSTKSIZ,$CC
+HBX_TMPSTK	.EQU	$
 ;
-HBX_BNKSTK	.EQU	$
+; INTERBANK COPY BOUNCE BUFFER (64 BYTES)
 ;
-; INTERBANK COPY BUFFER (64 BYTES)
+; N.B., THIS BUFFER IS ALSO USED AS A TEMPORARY STACK BY HBX_INVOKE.
+; THEREFORE, THIS BUFFER *CANNOT* BE USED TO PASS DATA OUTSIDE OF
+; HBIOS FUNCTION CALLS.
 ;
 HBX_BUF		.FILL	HBX_BUFSIZ,0
-;
-; TEMPORARY STACK FOR USE BY INVOKE, PEEK, AND POKE
-;
-HBX_TMPSTK	.EQU	$
+HBX_BUF_END	.EQU	$
 ;
 ; HBIOS PROXY MGMT BLOCK (TOP 32 BYTES)
 ;