added panic screen, added versioning mechanism proposal

c64/basic/commands/cmd_sys.s

@@ -0,0 +1,68 @@
+cmd_sys:
+	
+	jsr basic_end_of_statement_check
+	bcc !+
+
+	// SYS requires an argument
+	jmp do_SYNTAX_error
+	
+!:
+	//
+	// XXX Temporary ugly hack to support 'SYS PI*656'
+	//
+
+	ldy #$00
+
+cmd_sys_hack_loop:
+	lda (TXTPTR), y
+	cmp cmd_sys_hack_str, y
+	bne cmd_sys_hack_not_needed
+	lda (TXTPTR), y
+	beq cmd_sys_hack_apply
+	iny
+	bne cmd_sys_hack_loop // branch always
+
+cmd_sys_hack_apply:
+
+	lda #<2060
+	sta LINNUM+0
+	lda #>2060
+	sta LINNUM+1
+	bne cmd_sys_setup_call // always jumps
+
+cmd_sys_hack_not_needed:
+
+	//
+	// XXX End of hack
+	//
+
+	jsr basic_parse_line_number
+
+cmd_sys_setup_call:
+	lda #$4C // JMP opcode
+	sta USRPOK
+	lda LINNUM+0
+	sta USRADD+0
+	lda LINNUM+1
+	sta USRADD+1
+	
+	// Setup the register values
+	lda SPREG
+	pha
+	ldy SYREG
+	ldx SXREG
+	lda SAREG
+	plp
+
+	// Call the routine.
+	jsr USRPOK
+	
+	jmp basic_execute_statement
+
+
+	//
+	// XXX Temporary ugly hack to support 'SYS PI*656'
+	//
+
+cmd_sys_hack_str:
+	.byte $FF, $AC, $36, $35, $36, $00