; ; T h i n g T r a p ; ; ; Library support routine for routines that call the THING system ; trap. This routine allows for the fact that on many older systems ; (such as original QDOS) the TRAP#1 calls to the THING system are ; not available, and that a call has to be made via a THING vector ; instead. This is handled completely transparently. ; ; On entry, it is assumed that d0-d3 and a0-a3 are ; set up as though the trap was to be called. ; ; AMENDMENT HISTORY ; ~~~~~~~~~~~~~~~~~ ; 24 Jan 94 DJW - First version. Based on information from the ; QDOS Reference Manual from Jochen Merz, and checked ; against methods used in code of THING librarys from ; Lester Warehams and Johnathan Hudson. ; ; 13 Apr 94 DJW - The test for whether to use the vector or trap was ; flawed, and the code to go back to user mode was ; not correct on all paths. ; ; 14 Sep 94 DJW - Fixed bug in calling via vector - this stopped ; all calls from working on QDOS based systems. ; - Removed underscores from start of name. This makes ; it impossible to even call this routine directly ; from C by accident. ; - Put copy of this code into CRT_X startup module for ; use when RLLs are in use. .text .even .globl ThingTrap SMS.INFO equ $00 ; trap to get system informatopn SMS.NTHG equ $2b ; THING trap to get next in list SYS_THGL equ $b8 ; THING list offset in system variables TH_THING equ $10 ; THING base relative to linked list entry THH_TYPE equ $04 ; THING type offset THH_ENTR equ $08 ; THING entry routine pointer ERR.ITNF equ -7 ; Error: Not Found ERR.NIMP equ -19 ; Error: Mot Implemented thing_vector: dc.l 0 ; we use this to decide what to do ; 0 = do not know (initial state) ; -ve = TRAP interface available ; +ve = Address of UTILITY THING ThingTrap: move.l a4,-(sp) ; save register lea thing_vector(pc),a4 ; address we save vector at tst.l (a4) ; see if we know if traps supported bpl check_trap ; ... NO (or possibly unknown) ; This is the simplest case - the operating system DOES support ; the TRAP #1 interface to the THING system. use_trap: trap #1 rts_cond: move.l (sp)+,a4 tst.l d0 ; ensure condition code set rts ; If we get here, either the trap interface is not available, ; or possible we do not yet know the answer. check_trap: beq test_trap ; branch if unknown option. ; It appears that we do not have the trap interface available. ; We are now calling the THING system via the UTILITY THING. As a ; sanity check, we check that our vector still points to it. use_vector: move.l (a4),a4 ; get saved thing vector cmp.l #-1,THH_TYPE(a4) ; check it is still THING we want bne missing ; ... apparently not ? move.l THH_ENTR(a4),a4 ; OK, so entry vector jsr (a4) ; ... and take it bra rts_cond ; ... then normal exit setting condition ; Apparently we do not yet know - time to find out ; We do this be trying the TRAP #1 interface and seeing ; if we get a "Not Implemented" error. If not, then the ; calls must be available. test_trap: movem.l d0-d3/a0-a3,-(sp) ; save registers moveq #SMS.NTHG,d0 ; trap that always works if traps available sub.l a0,a0 ; ... get first THING in list trap #1 ; try using trap tst.l d0 ; did it work? movem.l (sp)+,d0-d3/a0-a3 ; first restore saved registers bne find_vector ; ... NO, then we need to find the vector ; We have found that the trap interface is available. ; Therefore set ourselves up to use this immediately on ; future calls. lea thing_vector(pc),a4 ; set to use trap in future subq.l #1,(a4) ; set vector negative to say trap OK bra use_trap ; go and use trap ; We have now determined that we need to use the UTILITY THING to call ; the THING system. The code to find this is based on that in the ; QDOS Reference manual. find_vector: movem.l d0-d3/a0,-(sp) ; save registers we might corrupt moveq #SMS.INFO,d0 trap #1 trap #0 ; enter Supervisor mode move.l SYS_THGL(a0),d1 ; this is THING list beq not_found ; ... empty, very bad move.l d1,a0 loop: move.l (a0),d1 ; get next list entry beq found ; end of list. Should be THING we want move.l d1,a0 ; follow link bra loop ; ... and try again ; The vector has been found. To avoid the ; overhead of repeating this check every time, ; we will save the address. found: move.l TH_THING(a0),a0 ; get THING base lea thing_vector(pc),a4 ; get address to save vector at move.l a0,(a4) ; ... and save result andi.w #$dfff,sr ; go back to user mode movem.l (sp)+,d0-d3/a0 ; restore registers we have corrupted. bra use_vector ; It appears that there is no support for the ; THING system loaded. Return an error code. not_found: andi.w #$dfff,sr ; go back to user mode movem.l (sp)+,d0-d3/a0 ; restore registers we have corrupted. missing: moveq #ERR.NIMP,d0 ; set not implemented error lea thing_vector(pc),a4 ; get vector address clr.l (a4) ; ... and ensure it is cleared bra rts_cond ; ... and exit