DSP ASSEMBLY LOCATION COUNTERS

The memory allocation macros described above use the following
corresponding location-counter assembly variables (listed along with
their actual initialization by DSPMACSRC/alloc.asm).  (The capitalized
address-boundary macros appear in DSPMACSRC/addresses.asm.)

 pi_lc     set PLI_USR    ; p internal memory is allocated UP from bottom
 pe_lc     set PLE_USR    ; p external memory is allocated UP from bottom
 xi_lc     set XLI_USR    ; x internal memory is allocated UP from bottom
 xe_lc     set XLE_USR    ; x external memory is allocated UP from bottom
 yi_lc     set YLI_USR    ; y internal memory is allocated UP from bottom
 ye_lc     set YLE_USR    ; y external memory is allocated UP from bottom
 li_lc     set XHI_USR    ; l internal memory is allocated DOWN from top
           if ONE_MEM==0  ; l external memory does not exist if ONE_MEM==1
 le_lc       set XHE_USR  ; l external memory is allocated DOWN from top
           else
 le_lc       set 'BAD_'   ; l external memory is allocated DOWN if it exists
           endif

Note that when external memory is shared (ONE_MEM==1), new_xeb and
new_yeb allocate against the same memory. In other words, pe_lc,
xe_lc, and ye_lc are all names for a single location counter.  In this
mode, long allocations (xy memory) are disallowed.

Each allocation LC is saved in the global assembly variables above so
that the user is free to use the LC's provided by the dsp assembler
(pl:, p:, ph:, xl:, etc.)  for other purposes. The "low" and "high"
LC's (e.g. xl:, yh:) are used internally by the allocation macros, but
this is hidden from the user by saving and restoring the LC value.

The user can reset the allocation pointers using the SET directive as
shown above in the case of initialization. 


"Overlays" are not supported; that is, the Runtime and Load LC are the
same.

 (!!! Problems with current allocation macros:
     - Can't deallocate
     - Constrained tables (for modulo addressing) are wasteful
 Fully general allocation macros will be simple once the yacc version
 of dspwrap exists.)