# HG changeset patch
# User Robert Gault <robert.gault@att.net>
# Date 1390688406 -3600
# Node ID 824019cd874451b359d0ab60d9011311cda7006c
# Parent  011a5f26e9da9f490b5ba7ae156ebef57540db16
rb1773: Make 48 TPI floppy disks readonly in 96 TPI drives

Deny the disk destroying write with the narrower heads of the 96 tpi drive
when the user has placed a 48 tpi disk in the 96 tpi drive so he can read
it. Double stepping the drive is then done automatically so as to stay in
mechanical synch with the tracks on a 48 tpi disk. But that, until now, did
not make the disk read-only, this patch does that.

Patch by Gene Heskett and Robert Gault.

diff -r 011a5f26e9da -r 824019cd8744 level1/modules/rb1773.asm
--- a/level1/modules/rb1773.asm	Sat Jan 25 23:19:38 2014 +0100
+++ b/level1/modules/rb1773.asm	Sat Jan 25 23:20:06 2014 +0100
@@ -85,6 +85,17 @@
 *
 *	2009/03/19	Robert Gault
 * Removed slow down hack from format and write sector but left code just in case.
+*
+*     2013/12/16 Robert Gault and Gene Heskett
+* Added two new flags, flagWP flagFMT, to prevent disk damage by Writes where
+* the drive head width does not match the disk track density.
+* flagWP <>0 write protects; flagFMT <>0 overrules flagWP so that a Format can
+* write to a disk.
+* A descriptor that does not match your drive can still cause Writes to disks that
+* could possibly cause disk corruption. This cannot be prevented.
+*
+* When LSN0 is read using a 3.5" drive, most of the checks of density, sides, etc.
+* are bypassed as not needed.
 
          nam   rb1773
          ttl   Western Digital 1773 Disk Controller Driver
@@ -172,6 +183,8 @@
 * physlsn  rmb   2              PCDOS (512 byte sector) #
 flag512  rmb   1              PCDOS (512 byte sector) 0=no, 1=yes
 flagform rmb   1              SCII format flag
+flagWP   rmb   1              write protection <>0
+flagFMT  rmb   1              format flag
 size     equ   .
 
          fcb   DIR.+SHARE.+PEXEC.+PWRIT.+PREAD.+EXEC.+UPDAT.
@@ -204,6 +217,8 @@
          clr   RW.Ctrl        clear SCII control register
          clr   flagform,u     clear SCII format flag
          ENDC
+         clr   flagWP,u
+         clr   flagFMT,u
          ldx   V.PORT,u       get Base port address
          lda   WD_Data,x      get byte at FDC Data register
          coma                 complement it to modify it
@@ -415,6 +430,10 @@
          ldy   >lastdrv,u     Get drive table ptr back
          lda   <DD.FMT,y      Get format for disk in drive
          ldy   2,s            restore path descriptor pointer
+* !!!!!!! Most of these tests are pointless with a 3.5" drive RG
+         ldb   <PD.TYP,y      Get path's type settings RG
+         bitb  #1             test for 3.5" drive
+         bne   L0128          skip rest of tests if 3.5" drive
          ldb   <PD.DNS,y      Get path's density settings
          bita  #FMT.DNS       Disk in drive double density?
          beq   L0115          No, all drives can read single, skip ahead
@@ -422,8 +441,10 @@
          beq   erbtyp         No, illegal
 L0115    bita  #FMT.TDNS      Is new disk 96tpi?
          beq   L011D          No, all drives handle 48/135 tpi, so skip ahead
+         sta   flagWP,u       set write protection
          bitb  #DNS.DTD       Can path dsc. handle 96 tpi?
          beq   erbtyp         No, illegal format
+         clr   flagWP,u       clear write protection since disk and descriptor match
 L011D    bita  #FMT.SIDE      Is new disk double sided?
          beq   L0128          No, all drives handle single sided, we're done
          lda   <PD.SID,y      Get # sides path dsc. can handle
@@ -661,7 +682,15 @@
 *    CC = carry set on error
 *    B  = error code
 *
-Write    lbsr  Chk512         go adjust LSN for 512 byte sector if needed
+Write    tst   flagFMT,u
+         bne   w3             if a format write normally and clear flags
+         tst   flagWP,u
+         beq   w2             continue if not a mismatch
+         ldb   #E$BTyp
+         lbra  L03E0          report bad type if forced WP
+w3       clr   flagFMT,u
+         clr   flagWP,u
+w2       lbsr  Chk512         go adjust LSN for 512 byte sector if needed
 * Next line was lda #%1001001 which was an error RG
          lda   #%10010001   retry flags for I/O errors (see Disto SCII source)
 L01C4    pshs  x,d            preserve LSN, retries
@@ -888,10 +917,17 @@
          bita  #%00000010     ??? (Base 0/1 for sector #?)
          bne   L02CC          Skip ahead
          incb                 Bump sector # up by 1
+*!!!!!!!!!!!!!!!!!!!!!critical section on double-stepping
 L02CC    stb   >DPort+WD_Sect Save into Sector register
          ldx   >lastdrv,u     Get last drive table accessed
          ldb   <V.TRAK,x      Get current track # on device
-         lda   <DD.FMT,x      Get drive format specs; actually disk format specs RG
+         lda   <PD.TYP,y      Get drive type
+         bita  #1             3.5" drive
+         beq   L02CCb         go if not 3.5" RG
+         lda   ,s             recover track #
+         clr   flagWP,u
+         bra   L02E9
+L02CCb   lda   <DD.FMT,x      Get drive format specs; actually disk format specs RG
          lsra                 Shift track & bit densities to match PD; bit0 is MF or MFM
          eora  <PD.DNS,y      Check for differences with path densities; bit0 is MF MFM, bit1 is 96tpi
          anda  #%00000010     Keep only 96 tpi
@@ -901,6 +937,8 @@
          beq   L02E9          No, continue normally
          lsla                 Yes, multiply track # by 2 ('double-step')
          lslb                 Multiply current track # by 2 ('double-step')
+         clr   flagWP,u
+         inc   flagWP,u       if double-step then prevent future writes
 L02E9    stb   >DPort+WD_Trak Save current track # onto controller
 
 * From here to the line before L0307 is for write precomp, but is not used.
@@ -1066,7 +1104,7 @@
 *         fcb   $8C
 
 *L03E0    ldb   #E$Read        Read error
-         orcc  #Carry         set carry
+L03E0    orcc  #Carry         set carry
          rts   
 
 L03E4    bsr   L0404          Send command to controller & waste some time
@@ -1127,7 +1165,9 @@
          ldb   #E$UnkSvc      return illegal service request error
          rts   
 
-SSWTrk   pshs  u,y            preserve register stack & descriptor
+SSWTrk   stb   flagFMT,u      permit unconditional write on format
+         clr   flagWP,u       don't protect on a format
+         pshs  u,y            preserve register stack & descriptor
 
 * Level 2 Code
          IFGT   Level-1