Filter
Top Products
Intel 8255x 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual 107
Host Software Interface
6.5.3.2 CU Resume Command
The CU Resume (CU_RESUME) command resumes CU operation. The 8255x completes the
following sequence:
1. If the CU is in the suspended state it goes to the active state and requests the beginning of the
next CB. Since the 8255x remembers the pointer to the next action command, it does not re-
read the link pointer in the previous CB. However, the 8255x re-reads the S bit in the previous
CB to determine if the driver has modified it while the device was suspended. If the S bit is
cleared, it proceeds to execute the new CB. If the S bit is still set in the previous CB, the CU
goes back to the suspended state.
2. If the CU is in the active state, it verifies the validity of the S bits in the current and next action
commands. If the S bit is cleared in the current CB, it proceeds to the next CB in the list after
execution of the current CB is completed.
3. If the CU is in the idle state, it ignores the CU_RESUME command.
6.5.3.3 CU Control Commands Response
The start and resume CU control (CUC) commands can be issued through the SCB CUC command
field. The command block offset pointer in the general pointer register of the SCB points to the first
executable action command. These action commands have a field for the end of list (EL) and
suspend (S) bits. The EL bit indicates that the current action command is the last on the command
list. The presence of the S bit indicates that the user wants the CU to enter the suspended state after
executing the current command. Table 54 and Table 55 illustrate the various state transitions.
The mechanism used to suspend the CU is the S bit in the action command block. Suspending the
CU through the action command block results in suspension after a specific command is executed.
The CU can be re-activated by issuing a resume command.
Table 54. CU Control Commands: Actions at Acceptance Time
Present State
CU Start CU Resume
Next State Action Next State Action
Idle Active
Start processing CB
pointed to by SCB
general pointer.
Idle None.
Suspended Active
Start processing CB
pointed to by SCB
general pointer.
Active
Start processing next CB
if S bit is clear on current
CB.
Active Prohibited Not applicable. Active
Re-check S bit on current
CB. If not set, process
next CB.
Table 55. CU Activities Performed at the End of Execution
EL Bit S Bit Next State Action
0 0 Active Start processing CB
0 1 Suspended CNA interrupt
1 0 Idle CNA/CI interrupt
1 1 Idle CNA/CI interrupt