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Annotation of xinu/sys/sizmem7300.s, revision 1.1.1.1

1.1       root        1: |* sizmem.s - sizmem */
                      2: 
                      3: MEMMAP =       0x400000
                      4: GCR    =       0xe40000
                      5: TPAT   =       0x5533
                      6: |*------------------------------------------------------------------------
                      7: |*  sizmem  --  size memory, placing highest valid address in _maxaddr
                      8: |*  for  ATT7300, all possible 4M acts real even if not there--
                      9: |*  have to detect wrapped memory addresses.  So write a test pattern
                     10: |*  to location 0 (not used for reset vector on this system), and
                     11: |*  then check each start of .5M block for same pattern.  When
                     12: |*  it shows up again, that's not really memory, just a reflection
                     13: |*  of prior memory.  This works for up to 2M of onboard memory.
                     14: |*  If you need more than that for Xinu, you're serious enough to
                     15: |*  know how to fix this for more memory.
                     16: |*------------------------------------------------------------------------
                     17:        .text
                     18:        .globl  _sizmem
                     19: _sizmem:
                     20:        clrl d0
                     21:        movl d0,a0        | moving pointer
                     22:        movw #TPAT,0      | put test pattern in loc 0
                     23:        movw #TPAT,d0     | and in d0
                     24: sizloop:
                     25:        addl #0x80000,a0  | next .5M block
                     26:        cmpl #0x200000,a0 | up to 2M of mem
                     27:        bge  sizdone
                     28:        cmpw a0@,d0       | ck for wrapped val showing up
                     29:        bne sizloop
                     30: sizdone:movl a0,d0        | here with wrap detected or 2M OK
                     31:        subl #4,d0        | Xinu wants last valid word, not first invalid
                     32:        movl d0,_maxaddr
                     33:        rts

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