40-4
MPC866 PowerQUICC Family User’s Manual
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Interrupt Queue Entry
40.2 Interrupt Queue Entry
Each entry in the ATM interrupt queue contains event information for a specic ATM
channel. During initialization, the host software should clear all queue entries and set the
wrap bit (W) only for the last entry. The format of an interrupt queue entry is shown in
5
DCC
DPLL carrier sense status change. Indicates carrier sense status generated by the DPLL has
changed state. The value of the DCC bit is valid only when the DPLL is enabled.
6–10
—
Reserved
11
SYNC Cell synchronization changed status. Indicates that the receiver has lost or gained cell delineation.
The SYNC interrupt is signaled whenever the receiver changes lock status (refer to the ASTATUS
If synchronization is lost (lock bit is cleared), the SYNC interrupt indicates a fatal ATM reassembly
error because the affected channels are unknown. When this happens, the receiver stops receiving
data from all channels and all data transfers to memory halt. After re-initializing the channels, the
host may resume receiving cells by executing the RESTART RECEIVE command (see Section 38.7, 12
IQOV
Interrupt queue overow. Set by the CP whenever an overow condition in the interrupt queue
occurs. This condition occurs if the CP attempts to write a new interrupt entry into a valid entry (V =
1) not yet handled by the host.
13
GINT
Global interrupt. Indicates that at least one new entry has been added to the interrupt queue. After
clearing the GINT event ag, the host begins processing the entries using the service pointer. The
host returns from the interrupt handler when it reaches an invalid queue entry (V = 0).
14
GUN
Global transmitter underrun. Indicates that an underrun occurred in the SCC transmitter FIFO. A
GUN error is fatal because the affected channels are unknown. After GUN is set, the transmitter
stops data transmission from all channels and sets the APC disabled status ag APCST[DIS]. The
transmit line enters an idle state (logic high). After re-initializing the channels, the host may resume
each channel.
For a faster recovery from a GUN error, re-initialize TSTATE by writing STFCR to the rst byte (MSB
of the 32 bit value representing xSTATE), clearing the second byte, and leaving the third and fourth
(LSB of the 32 bit value representing xSTATE) bytes as is. Then the APC can be restarted by clearing
APCST[DIS]. This procedure results in corrupted transmit frames initially. (TSTATE should normally
be modied only during system initialization.)
Note: Clearing APCST[DIS] may be overwritten by the APC scheduling process; therefore, the user
should verify that APCST[DIS] has indeed been cleared after a minimum of 50 system clocks.
15
GOV
Global receiver overrun. Indicates that an overrun occurred in the SCC receiver FIFO. A GOV error
is fatal because the affected channels are unknown. After GOV is set, the receiver stops receiving
data from all channels and halts all data transfers to memory. After re-initializing the channels the
For a faster recovery from a GOV error, re-initialize RSTATE by writing SRFCR to the rst byte (MSB
of the 32 bit value representing xSTATE), clearing the second byte, and leaving the third and fourth
(LSB of the 32 bit value representing xSTATE) bytes as is. This procedure initially results in corrupted
receive frames which should be disposed of by software. (RSTATE should normally be modied only
during system initialization.)
Table 40-2. Serial ATM Event Register (SCCE) Field Descriptions (continued)
Bits
Name
Description