tms: updated vram detection to disable screen during vram probing

Source/HBIOS/tms.asm

@@ -68,7 +68,8 @@
 ; Unused:		$????	$????
 ;
 TMSCTRL1:	.EQU	1		; CONTROL BITS
-TMSINTEN:	.EQU	5		; INTERRUPT ENABLE BIT
+TMSINTEN:	.EQU	5		; IEO - INTERRUPT ENABLE BIT
+TMSDISEN:	.EQU	6		;  BL - DISPLAY ENABLE BIT
 ;
 TMSKBD_NONE	.EQU	0
 TMSKBD_KBD	.EQU	1
@@ -1003,6 +1004,13 @@ TMS_VRMPRB_1MB:
 	RET				; AND RETURN
 ;
 TMS_VRMPRB1:
+	; DISABLE SCREEN WHILE PROBING RAM
+	; TO REDUCE MEMORY LATENCY ISSUES
+	LD	C,TMSCTRL1		; REGISTER #1
+	LD	A,(TMS_INITVDU_REG_1)	; VALUE TO SET
+	RES	TMSDISEN,A		; CLEAR TO DISABLE SCREEN
+	CALL	TMS_SET_X		; DO IT
+
 	; START OF REAL VRAM PROBING
 	LD	A,4			; SET RETURN VALUE FOR 64K
 	EX	AF,AF'
@@ -1078,6 +1086,11 @@ VRAMSIZE_DONE:
 	XOR	A
 	LD	C,14
 	CALL	TMS_SET_X
+
+	; RE-EANBLE DISPLAY
+	LD	C,TMSCTRL1		; REGISTER #1
+	LD	A,(TMS_INITVDU_REG_1)	; VALUE TO SET
+	CALL	TMS_SET_X		; DO IT
 ;
 	EX	AF, AF'
 	RET