There is a disassembly of 1770 DFS at: http://regregex.bbcmicro.net/dfs224.asm.txt
Thinking aloud, here, there are three ROM service calls that may be interesting:
&03 - boot filing system (pmsg in the disassembly).
&04 - unknown OS command (for *DISC) (chkcom in the disassembly)
&12 - initialise filing system (inifsy in the disassembly).
The *DISC command goes to the label 'init' in the disassembly. The service call to start a filing system is handled by this:so this ends up at the same place as *DISC. The "boot" entry is more interesting, and immediately next in the ROM:
Next we have code reach from various of the above:So all routines to starting DFS seem to end up at the label sinit0. *DISC and the ROM service call to start a filing system set A to &FF to attempt a warm start. The filing system boot call (&03) sets this according to whether the OS says it should attempt to use the !BOOT file and what keys are pressed.
Even if DFS is asked to do a warm start, there is this bit:So if DFS has saved things in its private workspace to enable a warm start it sets this flag. If there is something else there, there is a chance that this flag will be clear (bit 7 not set) in which case DFS will do a cold start anyway. It looks like there are three ways to make sure, though:
1. Find the DFS private workspace from the table the OS keeps, then use the correct offset (from the source/disassembly) to set this byte to zero.
2. Assume DFS is the only ROM that has private workspace and that nothing else has increased the size of the shared workspace and hard code that address.
3. Clear (set to zero) all memory between &0E00 and the proper value of OSHWM.
Thinking aloud, here, there are three ROM service calls that may be interesting:
&03 - boot filing system (pmsg in the disassembly).
&04 - unknown OS command (for *DISC) (chkcom in the disassembly)
&12 - initialise filing system (inifsy in the disassembly).
The *DISC command goes to the label 'init' in the disassembly. The service call to start a filing system is handled by this:
Code:
.inifsy ;Service call $12 = initialise FS JSR savita CPY #$04 ;if number of FS to initialise = 4 BEQ init ;then initialise DFS RTS ;else exitCode:
.pmsg ;Service call $03 = boot filing system JSR savita STY itemp ;save boot flag in scratch space LDA #$7A ;call OSBYTE $7A = scan keyboard from $10+ JSR osbyte TXA ;test returned key code BMI L9B54 ;if N=1 no key is pressed, so init and boot CMP #$32 ;else if key pressed is D BEQ L9B4F ;then register keypress, init and boot CMP #$61 ;else if key pressed is not Z BNE L9B0E ;then exit JSR LA9FB ;else set up i8271/MOS 1.20 emulation:.L9B4F LDA #$78 ;OSBYTE $78 = write keys pressed information JSR osbyte.L9B54 LDA itemp ;a=boot flag passed to service call JSR vstrng EQUS "Acorn 1770 DFS" EQUB $0D EQUB $0D ;iff A=0 then force cold start, enable bootIF _NMOS BCC sinit0 ;branch alwaysELSE BRA sinit0 ;65C02 instructionENDIFCode:
.init LDA #$FF ;$FF = allow warm start, disable boot.sinit0 JSR wopa ;have A=0 returned on exit.L9B70 PHA ;save cold start flag LDA #$06 ;FSC 6 = new filing system starting up JSR osfscm ;issue Filing System call LDA fdcdat LDX #$0D ;7 vectors to replace:.init0 LDA vtabb,X ;copy addresses of extended vector handlers STA vtab2,X ;to FILEV,ARGSV,BGETV,BPUTV,GBPBV,FINDV,FSCV DEX ;loop until 7 vectors transferred BPL init0 LDA #$A8 ;call OSBYTE $A8 = get ext. vector table addr JSR readby STX temp+$00 ;set up pointer to vector table STY temp+$01 LDX #$07 ;7 vectors to transfer LDY #$1B ;y = $1B = offset of FILEV in extended vector table:.init1 LDA vtabf-$1B,Y ;get LSB action address from table STA (temp),Y ;store in extended vector table INY LDA vtabf-$1B,Y ;get MSB action address from table STA (temp),Y ;store in extended vector table INY LDA romid ;get our ROM slot number STA (temp),Y ;store in extended vector table INY DEX ;loop until 7 vectors transferred BNE init1 STY catdrv ;no catalogue in workspace STY olddrv ;redundant STX fdrive ;[D]current drive = 0 LDA #$FF STA LC287 ;both drives uncalibrated LDY #$03.L9BB4 STA LC28B,Y ;clear bad tracks, $FF = rogue value DEY BPL L9BB4 LDX #$0F ;service call $0F = vectors claimed JSR doswcl ;call OSBYTE $8F = issue service call JSR suspri ;set up pointer to private page LDY #colds-mainws ;test cold start flag in private page LDA (temp),Y BPL initcl ;if b7=0 then force a cold start PLA ;else test cold start flag passed to us PHA BEQ initcl ;if =$00 then force a cold start LDY #memflg ;else test shared workspace possession flag LDA (temp),Y BMI bootit ;if b7=1 then we have the workspace, proceed to boot JSR getmem ;else issue service call $0A to claim the workspace LDY #$00 ;offset into private page = $00....Even if DFS is asked to do a warm start, there is this bit:
Code:
LDY #colds-mainws ;test cold start flag in private page LDA (temp),Y BPL initcl ;if b7=0 then force a cold start1. Find the DFS private workspace from the table the OS keeps, then use the correct offset (from the source/disassembly) to set this byte to zero.
2. Assume DFS is the only ROM that has private workspace and that nothing else has increased the size of the shared workspace and hard code that address.
3. Clear (set to zero) all memory between &0E00 and the proper value of OSHWM.
Statistics: Posted by Coeus — Wed Jan 22, 2025 8:53 pm