Motorola PowerQUICC II MPC8280 Series Reference Manual page 1246

IMA Programming Model
Table 34-10. IMA Group Receive Table Entry (continued)
Offset Name
0x2A STALL_THR
0x2B IRGFS
0x2C —
0x30 LINK_DCBO
0x34– —
0x3F
1
Boldfaced entries indicate parameters that must be initialized by the user. All other parameters are
managed by the microcode and should be initialized to zero unless otherwise stated.
34.4.4.2.1 IMA Group Receive Control (IGRCNTL)
The fields of the IGRCNTL register are shown in Figure 34-17.
0
Field GOTP
Figure 34-17. IMA Group Receive Control (IGRCNTL)
34-36
Freescale Semiconductor, Inc.
Width
Byte Stall threshold. Used to detect stalled links when performing
round-robin cell extraction from the delay compensation buffers (Dcbz).
This is the number of cells which may be received without advancing
the cell extraction pointer.
The value is application-dependent and must be tuned by the user to
the "expected worst case." Its value depends on the depth of queues
and FIFOs in the complete transmit/receive path, and the 'burstiness'
of the behavior of the FIFOs. Assuming very bursty FIFOs, it is
approximately:
STALL_THR = 2 x RNUMLINKS x (3 + RX_FIFO)
where:
a) RNUMLINKS is the number of links in the receive group order
structure (regardless of link status).
b) RX_FIFO is the depth of the receive FIFOs of the TC layer.
c) 3 is the rounded value of the allowed transmit skew between links of
a group (2.5, per the IMA standard).
An optimal value for STALL_THR will be great enough to produce no
link stall events in normal operation, but low enough to detect a failed
link as quickly as possible.
Byte IMA Receive Group Frame Size
Bits 0-5: Reserved
Bits 6-7 - GSC_M: Value of received ICP cell Group Status Contl field
(Bits 1:0) which determine the IMA frame size. This field must be
programmed before links in the group are assigned
Word Reserved. Must be initialized to zero at group startups.
Word Link DCB overflow interrupt indication. Bit array identifying which links
have issued a link DCB overflow (DCBO) interrupt. This parameter
ensures that only one DCBO interrupt is generated per event.
Microcode managed parameter. Initialize to zero at group startup.
3 Words Reserved. Must be initialized to zero at group startups.
1 2
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Description
3 4 5
RXSC IDCR
1
6 7
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