Certain OSBYTE calls are supported by Matrix Brandy, either by
CALL &FFF4 or result%=USR&FFF4, or SYS "OS_Byte",A[,X[,Y]]

Where a return value is supported, it will be &00YYXXAA.

Supported OSBYTE calls are:
A=0:
	X=0: return the MOS version as an error.
	X=1: Return the OS version in the X register (as per the 'use' doc)

A=42:	[Brandy only] Get or set various states
	If NO bits set: return state in X register.
	If ALL bits set: Analogue of Linux's "stty sane" - enables Refresh,
		issues a VDU 6 and sets both video bank controls to 0.
	Bits 0 and 1 control or contain the *REFRESH state:
	  00: No operation.
	  01: Equivalent to *REFRESH OFF
	  10: Equivalent to *REFRESH ON
	  11: Equivalent to *REFRESH ONERROR
	  Returned values: 01, 10 or 11.
	Bits 2 and 3 control or contain the Full Screen state:
	  00: No operation.
	  01: Full Screen Off.
	  10: Full Screen On.
	  11: Full Screen Toggle.
	  Returned values: 00 (off) or 10 (on).
	Bit 4: If set, do immediate display refresh, equivalent to *REFRESH
	  Value not returned.
A=43:	[Brandy only] Perform a VDU X to the controlling Linux terminal.
A=44:	[Brandy only] X=1: CTRL-N and CTRL-P do line editing (default).
		      X=0: CTRL-N and CTRL-P just send their codes.
			   Arrow keys still do line editing.
A=106	Select mouse pointer. Due to SDL limitations, this simply turns the
	pointer on or off, and unlinking does nothing.
A=112:	Selects which video bank the VDU drivers access. 4 available.
A=113:	Selects which video bank is drawn to the display window.
A=129:	INKEY. As with BASIC INKEY, scanning for range of keys not supported.
A=130:	High word of user memory.
A=131:	Bottom of user memory.
A=132:	Top of user memory
A=134:	Return text cursor position in X and Y. Identical to 165.
A=135:	Return screen mode and character under cursor or 0 if unreadable.
	In Brandy, the character under the cursor is only returned in MODE 7.
A=160:	Read VDU variable (equivalent to VDU(X%))
A=163:	Application Support - all these are local to Brandy
	X=1: Get or set refresh state (as per *REFRESH)
		Y=0: Equivalent to *REFRESH OFF
		Y=1: Equivalent to *REFRESH ON
		Y=2: Equivalent to *REFRESH ONERROR
		Y=255: Query the state, will return 0, 1 or 2 in Y register.
	X=127: Analogue of Linux's "stty sane" - enables Refresh, issues a
	       VDU 6 and sets both video bank controls to 0.
A=165	Return text cursor position in X and Y. Identical to 134.
A=200:	Set ESCAPE and BREAK effect - only ESCAPE effect supported.
A=229:	Enable or disable ESCAPE, disabled if X non-zero.
A=250:	X must equal 0, Y must equal 255. Get display write bank set with
	OSBYTE 112 returned in X register and display video bank set with
	OSBYTE 113 returned in Y register.
A=251:	X must equal 0, Y must equal 255. Get display video bank set with
	OSBYTE 113 returned in X register.

OSBYTEs 166-255 read and write OSBYTE system variables with new=(old AND Y) EOR X,
but only those listed have any effect.
