Freescale Semiconductor MPC8260 - Manual (Page 1140)

Inverse Multiplexing for ATM (IMA)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
33-38 Freescale Semiconductor
33.4.4.2.1 IMA Group Receive Control (IGRCNTL)
The fields of the IGRCNTL register are shown in Figure 33-17 .
Table 33-11 describes the IGRCNTL bit fields.
0x2A STALL_THR 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.
0x2B IRGFS 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
0x2C — Word Reserved. Must be initialized to zero at group startups.
0x30 LINK_DCBO 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.
0x34–
0x3F — 3 Words Reserved. Must be initialized to zero at group startups.
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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.
0 1 2 3 4 5 6 7
Field GOTP — RXSC IDCR —
Figure 33-17. IMA Group Receive Control (IGRCNTL)
Table 33-10. IMA Group Receive Table Entry (continued)
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Offset Name Width Description