
IBM3206K0424
IBM Processor for Network Resources
Preliminary
On-chip Checksum and DRAM Test Support (CHKSM)
Page 440 of 676
pnr25.chapt05.01
August 14, 2000
16.8: CHKSM Control Register
The various bits in this register control the mode in which the checksum entity operates. See 
Note on 
Set/Clear Type Registers on page 93
 for more details on addressing.
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, the CHKSM TCP/IP Checksum Data Register is 
set to 
’
0
’
. This option should be used if the TCP/IP checksum should never be set to 
’
0
’
(0xffff is 
‘
0
’
 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 0 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 
aliment 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 significant 
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 signifi-
cant 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.
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.
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.