
IBM2520L8767
IBM Processor for ATM Resources
On-chip Checksum and DRAM Test Support (CHKSM)
Page 352 of 553
atmrm.chapt05.01
08/27/99
17.8: CHKSM Control Register
The various bits in this register control the mode in which the checksum entity operates. See
Note on
Set/Clear/Read Type Registers
on page 71 for more details on addressing. The various bits are described
below:
Length
13 bits
Type
Clear/Set
Address
XXXX 0A28 and 2c
Power On Value
X’00’
Restrictions
None
C
E
H
S
I
R
C
R
M
R
T
E
E
12 11 10
9
8
7
6
5
4
3
2
1
0
Bit(s)
Name
Description
12
CL-FF -- Clear to All Ones
When this bit is set, the CHKSM TCP/IP Checksum Data Register is set to 0xffff when
it is cleared. When this bit is cleared, it is the CHKSM TCP/IP Checksum Data Register
is set to zero when it is cleared. This option should be used if the TCP/IP checksum
should never be set to zero (0xffff is zero also).
11
EX-AL -- Expose Alignment
When this bit is set, the internal checksum alignment is exposed for reading/writing.
For writes, bit 16 of the write data is used to set the internal alignment. For reads, the
alignment is exposed in bit 16 or bit zero depending on the value of the HI-LO bit in this
register. This can be useful if doing non-consecutive multiple part check sums (need to
preserve alignment between chunks). When this bit is cleared, the internal checksum
alignment is not exposed. It is always cleared when the CL-IP bit in this register is set.
Normally the internal alignment is calculated and maintained across consecutive check
sums.
10
HI-LO -- Hi Lo Word
When this bit is set, the checksum data register data is placed in the most sig 16 bits of
the 32 bit value read. When this bit is cleared, the checksum data register data is
placed in the least significant 16 bits of the 32 bit value read. This bit does not affect
how writes to the checksum data register occur, the data from the least significant 16
bits is always used.
9
SW-SUM -- Swap CheckSum
When this bit is set, the checksum data register data is byte-swapped when read.
When this bit is cleared, the checksum data register data is read normally.
8
IN-SUM -- Invert CheckSum
When this bit is set, the checksum data register data is inverted when read. When this
bit is cleared, the checksum data register data is read normally.
There are also new checksum data register addresses that can be read that do the
same thing as this control bit. This bit is depreciated.