emulator: Add code for lseek() rather than the UZI v6 seek

Not yet tested, but this should be the basis to bootstrap CP/M emulation
code in the OS environment. At that point we can retarget the UZIX native
compiler setup for FUZIX and have a native compiler for userspace (yay!)

diff --git a/Kernel/cpm-emulator/emulator.s b/Kernel/cpm-emulator/emulator.s
index de59650..1dc259f 100644 (file)
--- a/Kernel/cpm-emulator/emulator.s
+++ b/Kernel/cpm-emulator/emulator.s
@@ -1,5 +1,9 @@
     ; must begin on a page boundary (address % 256 == 0) to ensure
     ; the jump table is correctly aligned
+    ;
+    ; This varies by platform so we really want to make this relocatable
+    ; not linked per platform somehow
+    ;
     .org 0xf000
 startaddr:
 
@@ -13,6 +17,7 @@ ESC       EQU     1BH             ; ASCII ESCape Char
 
 TCGETS   EQU     1               ; Fuzix - get tty data
 TCSETS    EQU     2               ; Fuzix - set tty data
+TIOCINQ   EQU    5               ; Fuzix - characters pending
 
 STDIN     EQU     0               ; file descriptor value of keyboard
 STDOUT    EQU     1               ; file descriptor value of display
@@ -541,7 +546,7 @@ Fcn17:      CALL    CkSrch          ; Ensure Search File closed
 ;         case 18: return (255);                       /* Search Next */
 
 ;
-;      FIXME: dir entries need to be bigger
+;      FIXME: dir entries need to be bigger ?
 ;
 Fcn18: LD      HL,(dmaadr)
        LD      (dmaSav),HL     ; Save "real" DMA
@@ -621,8 +626,7 @@ Fcn33:      CALL    RWprep          ; Prepare File for access
 
 ;....
 DoRead:
-       CALL    SkOff           ; Seek to Offset (128-byte rec in Block)
-       CALL    SkBlk           ; Seek to 512-byte Block
+       CALL    LSeek           ; Seek to Offset (128-byte rec in Block)
 
        CALL    BRead           ; Read 1 Sector
 
@@ -687,8 +691,7 @@ Fcn34:      CALL    RWprep          ; Prepare file for access
 
 ;....
 DoWrite:
-       CALL    SkOff           ; Seek to Offset (128-byte rec in Block)
-       CALL    SkBlk           ; Seek to 512-byte Block
+       CALL    LSeek           ; Seek to Offset (128-byte rec in Block)
 
        CALL    BWrit           ; Write 1 Sector
 
@@ -1017,38 +1020,44 @@ GetNX:  LD      (IX+0),0
 ;
 ;      FIXME: we need to use lseek for Fuzix
 ;
-;.....
-; Seek Offset.  Uses Record Count to set 128-byte offset in 512-byte Sctr.
-
-SkOff: LD      BC,0
-       PUSH    BC              ; 0 Mode (Absolute Offset Position)
-       LD      IY,(_arg)       ; Pt to current fcb
-       LD      A,(IY+32)       ; Fetch Lo Byte of Offset
-       AND     03H             ;  (kill all but mod 512, 2 bits)
-       LD      B,A
-       SRL     B
-       RR      C               ;   Offset is pos'n within 512-byte Rec
-       JR      SeekV           ;  ..finish in Common Code
-
-;.....
-; Seek Block.  Uses Record Count to set Div-512 Block Number
-
-SkBlk: LD      HL,3            ; 3 Mode (Absolute Block Position)
-       PUSH    HL              ;  to Stk
-       LD      IY,(_arg)
-       LD      C,(IY+32)
-       LD      B,(IY+12)
-       SRL     B
-       RR      C
-       SRL     B
-       RR      C               ;   Blk # is DIV 512
-SeekV: PUSH    BC
-       LD      HL,(curFil)     ;    fd
+LSeek: LD      BC, 0           ; Push 0 for absolute
+       PUSH    BC
+       LD      IY, (_arg)      ; FCB
+       LD      C, (IY + 32)    ; Pull the offset out of the FCB
+       LD      B, (IY + 12)    ; This is in records (128 bytes)
+                               ; And may overflow 2^16 bytes
+       XOR     A
+       SLA     C               ; C x 2, into carry
+       RL      B               ; B x 2 picking up carry from C
+       RLA                     ; A x 2 picking up carry from B - now in 64's
+       SLA     C
+       RL      B
+       RLA                     ; now in 32's
+       SLA     C
+       RL      B
+       RLA                     ; now in 16's
+       SLA     C
+       RL      B
+       RLA                     ; now in 8's
+       SLA     C
+       RL      B
+       RLA                     ; now in 4's
+       SLA     C
+       RL      B
+       RLA                     ; now in 2's
+       SLA     C
+       RL      B
+       RLA                     ; now in bytes
+       LD      (LSeekData), BC ; low bits
+       LD      (LSeekData + 2), A      ; high bit (top byte already clear)
+       LD      BC, LSeekData   ; push pointer
+       PUSH    BC
+       LD      HL, (curFil)
        PUSH    HL
-       LD      HL,9            ;     UZI Seek Fcn #
+       LD      HL, 9           ; _lseek()
        PUSH    HL
-       RST     30H             ;      Execute!
-       POP     BC
+       RST     30H             ; Syscall
+       POP     BC              ; Recover stack
        POP     BC
        POP     BC
        POP     BC
@@ -1530,6 +1539,8 @@ dmaSav:   DEFW    0               ; Temp storage of current DMA Address
 srchFD:        DEFW    0               ; File Descriptor for Searches
 char:  DEFB    ' '             ; Byte storage for Conin/Conout
 cnt:   DEFW    0               ; Count of waiting keys
+LSeekData:     DEFW    0       ; Used for _lseek() syscalls
+               DEFW    0
 ttTermios:
        DEFS    20              ; Working TTY Port Settings
 ttTermios0: