; MesabROM.Mu - Registers, miscellaneous symbols and constants
; Last modified by Levin - October 23, 1978  10:08 AM

; R memories used by code in ROM0, correct to AltoCode23.Mu

; Nova Emulator Registers (some used by Mesa as well)

$AC3		$R0;
$MASK1		$R0;
$AC2		$R1;
$AC1		$R2;
$YMUL		$R2;
$RETN		$R2;
$AC0		$R3;
$SKEW		$R3;
$NWW		$R4;
$SAD		$R5;
$CYRET		$R5;
$TEMP		$R5;
$PC		$R6;
$XREG		$R7;
$WIDTH		$R7;
$PLIER		$R7;
$XH		$R10;
$DESTY		$R10;
$WORD2		$R10;
$DWAX		$R35;
$MASK		$R36;
$SWA		$R36;
$DESTX		$R36;
$LREG		$R40;
$NLINES		$R41;
$RAST1		$R42;
$SRCX		$R43;
$SKMSK		$R43;
$SRCY		$R44;
$RAST2		$R44;
$CONST		$R45;
$TWICE		$R45;
$HCNT		$R46;
$VINC		$R46;
$HINC		$R47;
$NWORDS		$R50;
$MASK2		$R51;
; Registers used by standard Nova I/O controllers
;	All names have been prefixed with 'x' to prevent conflicts when MesabROM is
;	used by XMesa clients to assemble MesaXRAM with other microcode.

; Model 31 Disk

$xKWDCT		$R31;
$xKWDCTW	$R31;
$xCKSUMR	$R32;
$xKNMAR		$R33;
$xKNMARW	$R33;
$xDCBR		$R34;

; Display

$CURX		$R20;
$xCBA		$R22;
$xAECL		$R23;
$xSLC		$R24;
$xMTEMP		$R25;
$xHTAB		$R26;
$xYPOS		$R27;
$xDWA		$R30;

; Ethernet

$xECNTR		$R12;
$xEPNTR		$R13;

; Memory Refresh

$xR37		$R37;

; Audio (obsolete)

$xAudioWdCt	$R71;
$xAudioData	$R72;
; Registers used by Mesa Emulator

; R registers

$temp		$R35;			Temporary (smashed by BITBLT)
$temp2		$R36;			Temporary (smashed by BITBLT)
$mpc		$R15;			R register holds Mesa PC (points at word last read)
$stkp		$R16;			stack pointer [0-10] 0 empty, 10 full
$XTSreg		$R17;			xfer trap state

; Registers shared by Nova and Mesa emulators
;	Nova ACs are set explicitly by Mesa process opcodes and for ROM0 calls
;	Other R-registers smashed by BITBLT and other ROM0 subroutines

$brkbyte	$R0;			(AC3) bytecode to execute after a breakpoint
;					Warning! brkbyte must be reset to 0 after ROM calls!
;					(see BITBLT)
$mx		$R1;			(AC2) x register for XFER
;					Warning! smashed by BITBLT and MUL/DIV/LDIV
$saveret	$R2;			(AC1) R-temporary for return indices and values
$newfield	$R3;			(AC0) new field bits for WF and friends
;					Warning! must be R-register; assumed safe across CYCLE

$count		$R5;			scratch R register used for counting
$taskhole	$R7;			pigeonhole for saving things across TASKs
;					Warning! smashed by all ROM calls!
$ib		$R10;			instruction byte, 0 if none (0,,byte)
;					Warning! smashed by BITBLT
$clockreg	$R37;			low-order bits of real-time clock

; S registers, can't shift into them, BUS not zero while storing.

$my		$R51;			y register for XFER
$lp		$R52;			local pointer
$gp		$R53;			global pointer
$cp		$R54;			code pointer
$ATPreg		$R55;			allocation trap parameter
$OTPreg		$R56;			other trap parameter
$XTPreg		$R57;			xfer trap parameter
$wdc		$R70;			wakeup disable counter

; Mesa evaluation stack

$stk0		$R60;			stack (bottom)
$stk1		$R61;			stack
$stk2		$R62;			stack
$stk3		$R63;			stack
$stk4		$R64;			stack
$stk5		$R65;			stack
$stk6		$R66;			stack
$stk7		$R67;			stack (top)

; Miscellaneous S registers

$mask		$R41;			used by string instructions, among others
$unused1	$R42;			not safe across call to BITBLT
$unused2	$R43;			not safe across call to BITBLT
$alpha		$R44;			alpha byte (among other things)
$index		$R45;			frame size index (among other things)
$entry		$R46;			allocation table entry address (among other things)
$frame		$R47;			allocated frame pointer (among other things)
$righthalf	$R41;			right 4 bits of alpha or beta
$lefthalf	$R45;			left 4 bits of alpha or beta
$unused3	$R50;			not safe across call to BITBLT
; Mnemonic constants for subroutine return indices used by BUS dispatch.

$ret0		$L0,12000,100;			zero is always special
$ret1		$1;
$ret2		$2;
$ret3		$3;
$ret4		$4;
$ret5		$5;
$ret6		$6;
$ret7		$7;
$ret10		$10;
$ret11		$11;
$ret12		$12;
$ret13		$13;
$ret14		$14;
$ret15		$15;
$ret16		$16;
$ret17		$17;
$ret20		$20;
$ret21		$21;
$ret22		$22;
$ret23		$23;
$ret24		$24;
$ret25		$25;
$ret26		$26;
$ret27		$27;
$ret30		$30;
$ret31		$31;
$ret37		$37;
; Mesa Trap codes - index into sd vector

$sBRK			$L0,12000,100;		Breakpoint
$sStackUnderflow	$2;			(trap handler distinguishes underflow from
$sStackOverflow		$2;			overflow by stkp value)
$sXferTrap		$4;
$sAllocListEmpty	$6;
$sControlFault		$7;
$sCsegSwappedOut	$10;
$sUnbound		$13;

; Low- and high-core address definitions

$CurrentState	$23;				location holding address of current state
$NovaDVloc	$25;				dispatch vector for Nova code
$avm1		$777;				base of allocation vector for frames (-1)
$sdoffset	$60;				offset to base of sd from av
$gftm1		$1377;				base of global frame table (-1)
$BankReg	$177740;			address of emulator's bank register

; Constants in ROM, but with unpleasant names

$12		$12;				for function calls
$-12		$177766;			for Savestate
$400		$400;				for JB

; Frame offsets and other software/microcode agreements

$lpoffset	$6;				local frame overhead + 2
$nlpoffset	$177771;			= -(lpoffset + 1)
$nlpoffset1	$177770;			= -(lpoffset + 2)
$pcoffset	$1;				offset from local frame base to saved pc
$npcoffset	$5;				= -(lpoffset+1+pcoffset) [see Savpcinframe]
$retlinkoffset	$2;				offset from local frame base to return link
$nretlinkoffset	$177774;			= -(lpoffset-retlinkoffset)

$gpoffset	$4;				global frame overhead + 1
$ngpoffset	$177773;			= -(gpoffset + 1)
$gfioffset	$L0,12000,100;			offset from global frame base to gfi word (=0)
$ngfioffset	$4;				= gpoffset-gfioffset [see XferGfz]
$cpoffset	$1;				offset from global frame base to code pointer
$gpcpoffset	$2;				offset from high code pointer to global 1

$gfimask	$177600;			mask to isolate gfi in global frame word 0
$enmask		$37;				mask to isolate entry number/4

$maxallocslot	$23;				largest fsi microcode can handle

; Symbols to be used instead of ones in the standard definitions

$mACSOURCE	$L024016,000000,000000;		sets only F2.  ACSOURCE also sets BS and RSEL
$msr0		$L000000,012000,000100;		IDISP => 0, no IR← dispatch, a 'special' zero
$BUSAND~T	$L000000,054015,000040;		sets ALUF = 15B, doesn't require defined bus
; Linkages between ROM1 and RAM for overflow microcode

; Fixed locations in ROM1

$romnext	$L004400,0,0;					must correspond to next
$romIntstop	$L004406,0,0;					must correspond to Intstop

; Fixed locations in RAM

$ramBLTloop	$L004403,0,0;					must correspond to BLTloop
$ramBLTint	$L004405,0,0;					must correspond to BLTint