DAS ASSEMBLY DOCUMENTATION


 DAS asmfile [-o objectfile] [-E errorfile] [-nu]

 DAS is a minimal 68000 assembler designed to assemble the output of DC1

 DAS SHOULD NOT BE USED FOR ASSEMBLY PROJECTS, IT IS MEANT SOLELY TO DEAL
 WITH THE OUTPUT FROM THE COMPILER.

             
 OPTIONS

 -o objfile      specify object file, else uses asmfile.o (after
                 removing any trailer after the .)

 -E errorfile    specify file for errors, else stderr is used

 -nu             specify that the HUNK_UNIT have no name (for
                 libraries, to make the library smaller)



 NOTE:
     Das cannot handle expressions other than simple +,-,*, and /,
     and only one address label is allowed per expression (i.e.
     value unknown until link or load)

     Das does not understand integral types other than decimal and hex.

     Das does not understand strings 'string'.

     Das cannot export EQU labels (i.e. ABS references).

     Das has no macro facilities

                  
 FEATURES

 Das includes optimization features used by the compiler.  Also, Das can
 handle arbitrary forward referenced REG labels for MOVEM which most
 assemblers cannot.

 Das allows and automatically coagulates multiple occurances of section
 directives of the same name and type.

 Das automatically pads CODE sections with NOPs instead of 0's.  However,
 DS.L will always pad with 0.


 DAS handles the following directives:

 DC      declare data
 DS      declare space / align

 SECTION     declare a section.  Sections may be repeated to flip
         back and forth between them.  A third argument
         may contain a value to be ORd with the hunk
         type field, usually used to specify special
         hunk flags (i.e. hunk to chip memory, etc...)

 XREF        import a label
 XDEF        export a label
 EQU     declare a constant (must be a numerical constant)
 REG     declare zero or more registers in register list

 PROCSTART   used to determine procedure boundries for A5 check/
 PROCEND     link/unlk removal.  Also automatically sets optimization
         option to 1 if 0.

 DAS handles the following expressions:

 +, -, *, /, negation.  Only one relocatable label allowed per
 expression. Any number of EQU'd labels allowed, forward or reverse
 referenced.

 Optimization level 0 (default unless PROCSTART exists in file)

 * MOVEM's using 'reg' labels are optimized to either a MOVE or by
   removing the MOVEM entirely (reg labels that specify no registers).

 * BRANCHES to BRAs are optimized (up to 20 hops)
 * unsized BRANCHES are optimized to byte branches if possible
 * BRANCHES to the next instruction are deleted

 Optimization level 1  (automatic if PROCSTART exists in file)

 * LINK/UNLK within PROCSTART/PROCEND bounds is removed if the link
   register (currently hardwired to be A5) is never referenced AND if
   no subroutine calls are made within the procedure (JSR's or BSR's)

   This allows support of stack backtraces while optimizing most low
   level routines written in C.  Removal of LINK/UNLK in routines that
   make other subroutine calls does not yield much of an efficiency
   boost anyway.

 
 PROBLEMS

 DAS Uses an incredible amount of memory due to efficiency considerations
 in the optimization and myself wanting to keep it FAST.

 When specifying DIFFERENTLY NAMED CODE SECTIONS in the SAME ASSEMBLY FILE,
 keep in mind that the code sections are not necessarily near to each other
 in the final link and the linker cannot generate a jump table for
 PC-Relative inter-module calls.  Thus, one section calling another should
 not use PC-Relative unless you *know* your final executable is going to
 be less than 32K *AND* you do not use the -frag option to dlink.

 This is why the startup c.a references the autoinit sections with
 absolute calls instead of PC-relative calls.

 
 EFFECTIVE ADDRESS

 Dn  - data register D0-D7
 An  - addr register D0-D7
 .z  - size (.W or .L)
 *s  - 68020 scale (*1, *2, *4, *8)

 bd  - base displacement expression, Usually followed by base
   displacement size or (A4) to indicate a data-relative
   relocation.  Example:   xx+4.L  xx.W   23+xx(A4)

 od  - outer displacement expression, like bd.  Only allowed if an
   indirection [] is used.

                        68000   68020/030
 Dn                        x         x
 An                        x         x
 (An)                      x         x
 (An)+                     x         x
 -(An)                     x         x
 d16(An)                   x         x
 d8(An,Dn.z)               x         x
 d8(An,Dn.z*s)                       x
 (bd.z/(A4),An,Dn.z*s)               x     all items optional

 example: (foo(A4),A4,D0.W*8)
          (bar.L,D2.W*8)

 ([bd.z/(A4),An],Dn.z*s,od)          x
 ([bd.Z/(A4),An,Dn.z*s],od)          x