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38 Intel 8255x 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual
Host Software Interface
Bits 23:20 CUC
This field contains the CU Command. Valid values for this field are:
0000 NOP. The no operation command does not affect the current state of the
unit.
0001 CU Start. CU Start begins execution of the first command on the CBL. A
pointer to the first CB of the CBL should be placed in the SCB General Pointer
before issuing this command.
NOTE: The CU Start command should only be issued when the CU is in the
idle or suspended states (never when the CU is in the active state) and
all of the previously issued CBs have been processed and completed
by the CU. Sometimes, it is only possible to determine that all CBs are
completed by checking the complete bit in all previously issued
Command Blocks.
0010 CU Resume. The CU Resume command resumes CU operation by
executing the next command. If the CU is Idle, it ignores the CU Resume
command.
0100 Load Dump Counters Address. This command directs the device where to
write dump data when the Dump Statistical Counters or Dump and Reset
Statistical Counters command is used. It must be executed at least once before
the Dump Statistical Counters or Dump and Reset Statistical Counters
command is used. The address of the dump area must be placed in the general
pointer register.
0101 Dump Statistical Counters. This command directs the device to dump its
statistical counters to the area designated by the Load Dump Counters Address
command.
0110 Load CU Base. The internal CU Base Register is loaded with the value in
the SCB General Pointer.
0111 Dump and Reset Statistical Counters. This command directs the device to
first dump its statistical counters to the area designated by the Load Dump
Counters Address command and then to clear these counters.
1010 CU Static Resume. It resumes CU operation by executing the next
command. If the CU is idle, it will ignore the CU Resume command. This
command should be used only when the device CU is in the suspended state
and has no pending CU Resume commands. This command is only valid for the
82558 and later devices. It is not valid for the 82557.
Bit 19 Reserved This bit is reserved and should be set to 0.
Table 14. SCB Command Word Bits Descriptions
Bit Symbol Description