OSWORD &72 - Double Density Disk Access
                =======================================

OSWORD &72 passes a SCSI-style control block to the floppy or hard  disk
controller to access double density floppies or hard drives.

     On extry:
        XY+0=0, holds result on exit
        XY+1..4=address
        XY+5=command
        XY+6=drive number in b5-b7, sector b16-b20 in b0-b4
        XY+7=sector middle byte,
        XY+8=sector low byte,
        XY+9=number of sectors,
        XY+10=n/u,
        XY+11..14=data length if XY+9=0.

Note than the sector address is stored in big-endian form. The
drive number in XY+6 is ORed with ADFS's current drive. Most ADFS
implementations require ADFS to be the currently selected filing
system. The call silently returns if any other filing system is
selected.

        Commands include
 &08=Read data,
 &0A=Write data,
 &0B=Seek track.

 On exit, XY+0=result:
 &00=Ok
 &04=Not ready
 &40=Write protected
 &48=CRC error,
 &50=Sector not found,
 &60=Bad command,
 &61=Bad sector address
 &63=Volume error,
 &65=Bad drive.
 &6F=Abort

The following function can be used to perform the call. It requires
X%=>15-byte control block, Y%=X%DIV256.

DEFFNscsi(cmd%,addr%,num%,sect%,drv%):LOCAL fs%
fs%=FNfs:IF fs%<>8:*FX143,18,8
X%?0=0:X%!1=addr%:X%?5=cmd%:X%?6=drv%*32+((sect%AND&1F0000)DIV65536)
X%?7=((sect%AND&FF00)DIV256):X%?8=sect%:X%!9=num%DIV256:X%!11=num%
A%=114:CALL&FFF1:A%=?X%:IF fs%<>8:OSCLI"FX143,18,"+STR$ fs%
=A%
DEFFNfs:LOCAL A%,E%,Y%:=(USR&FFDA)AND&FF