AAL2 Implementation
MPC885 PowerQUICC Family Reference Manual, Rev. 2
44-14
Freescale Semiconductor
Table 44-4
describes the RPD fields.
0
1
2
3
4
6
7
8
15
0
E
—
W
INT
—
CM
—
2
—
E0
E1
E2
E3
E4
—
E6
E7
—
4
RP_PTR
6
Figure 44-6. Receive Packet Descriptor (RPD)
Table 44-4. RPD Field Descriptions
Offset
Bits
Name
Description
0x00
0
E
Empty. Determines whether the CPS-Packet is accessible to the host or AAL2.
0 The CPS-Packet associated with this RPD has been filled with the received packet, or
receiving has been aborted due to an error. Host is free to examine or to write to the
fields of this RPD. AAL2 will not access this RPD while the E bit is 0. Host should set
this bit after processing the CPS-Packet and RPD.
1 The CPS-Packet associated with this RPD is empty, or is currently being filled by AAL2.
This RPD and its associated CPS-Packet can be used by AAL2. Once the E bit is set,
the host should not modify any fields of this RPD. AAL2 clears this bit after it retrieves
the CPS-Packet and updates the RPD.
During host initialization, E bit should be set in all RPDs.
0x00
1
—
Reserved, should be cleared.
0x00
2
W
Wrap. Determines whether this is the last RPD in the AAL2_Rx_Queue.
0 This is not the last RPD in the AAL2_Rx_Queue.
1 This is the last RPD in the AAL2_Rx_Queue. After the CPS-Packet associated with this
RPD is retrieved from the active AAL0 buffer, the AAL2 returns to the beginning of the
queue (using the RPD pointed to by AAL2_RQ_BASE). The number of RPDs in the
queue is programmable and is determined only by the W bit.
This bit is configured by the host during initialization and is not modified by AAL2.
0x00
3
INT
Determines whether anAAL2 interrupt is generated after this CPS-Packet is retrieved.
0 No interrupt is generated after this CPS-Packet is filled.
1 After the CPS-Packet is retrieved (and if AAL2_RCT[RPI] is set), an entry is added to
the exception queue with the AAL2 bit and RXB bit set. The global interrupt count
(INT_CNT) is decremented. If the counter reaches zero, SCCE[GINT] or IDSR1[GINT]
is set, and an interrupt is generated to the host.
This bit is configured by the host and is not modified by the AAL2.
0x00
4–6
—
Reserved, should be cleared.
0x00
7
CM
Continuous mode. Determines whether the CPS-Packet associated with this RPD is
marked as available to the host (E=0) after processing by the CP.
0 Normal operation.
1 The E bit is not cleared after the RPD is closed, allowing the associated CPS-Packet to
be automatically rewritten the next time the CP accesses this RPD.
Host writes this field during initialization. AAL2 does not modify this field.
0x00
4–15
—
Reserved, should be cleared.
0x02
0–5
—
Reserved, should be cleared.
Summary of Contents for PowerQUICC MPC870
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