TC1796
System Units (Vol. 1 of 2)
Data Memory Unit
User’s Manual 8-17 V2.0, 2007-07
DMU, V2.0
Field Bits Type Description
OMASK [8:1] rw Overlay Address Mask
This bit field determines two parameters:
• Block size of the overlay memory block x
• Address bits taken for address generation
The mask bits determine which address bits are taken
to check if a target address is overlayed, and
determines which address bits are taken from the
original target address as offset, and which are taken
from RABRx.OBASE. Thus the mask also determines
the block size of the overlay block.
0
B
Corresponding address bits are not used in the
address comparison
Corresponding final address bits are derived
from the original address
Block size is 2
n
bytes, n = number of trailing
zeros in the register
1
B
Corresponding address bits are used in the
address comparison
Corresponding final address bits are derived
from RABR_OBASE
Block size is 2
n
bytes, n = number of trailing
zeros in the register
All OMASK bits located right of the most significant
mask bit which is set to zero, are treated as zeros as
well, independent from their actual value. They will be
read back as 0.
Selected overlay memory block size:
00000000
B
512 bytes
10000000
B
256 bytes
11000000
B
128 bytes
11100000
B
64 bytes
11110000
B
32 bytes
11111000
B
16 bytes
11111100
B
8 bytes
11111110
B
4 bytes
11111111
B
2 bytes
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