MPC8280 datasheet(894/1386 Pages) FREESCALE

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Multi-Channel Controllers (MCCs)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

29-4

Freescale Semiconductor

29.2

Global MCC Parameters

The global MCC parameters are described in Table 29-1.

Table 29-1. Global MCC Parameters

Offset1

Name

Width

Description

0x00

MCCBASE

Word

MCC base pointer. User-initialized parameter points to the starting address of a

512-Kbyte BD segment in external memory.

0x04

MCCSTATE

Hword MCC state. Used by the CP for global state definition. Should be cleared during

initialization.

0x06

MRBLR

Hword Maximum receive buffer length (user-initialized). Defines the maximum number of

bytes written to a receive buffer before moving to the next buffer for this channel. This

value must be a multiple of 8.

0x08

GRFTHR

Hword Global receive frame threshold. Used to reduce interrupt overhead that would

otherwise occur when many short HDLC frames arrive that each cause an RXF

interrupt. Programming GRFTHR can be used to limit the frequency of RXF

interrupts. In normal operation, an unmasked RXF event is written to the interrupt

table on each received frame. However, a user may choose to mask the RXF event

and program GRFTHR instead. If the user places a non-zero value in GRFTHR,

RINT

x is asserted in the MCC event register when the number of RXF events reaches

the GRFTHR value. Therefore, note that in addition to indicating new interrupt queue

entries, the assertion of RINT

x could then also be due to the threshold of received

frames being reached due to activity on any of this MCC’s receive channels.

Therefore, software should look for frames in all active buffer descriptor rings. This

parameter does not need to be reset after an interrupt.

0x0A

GRFCNT

Hword Global receive frame count. A down counter used to implement the GRFTHR feature.

It should be initialized to the GRFTHR value. The CP writes an entry in a circular

interrupt table and decrements GRFCNT each time a frame is received. When

GRFCNT reaches zero, the CP generates an interrupt and re-initializes GRFCNT with

GRFTHR. This parameter does not need to be reset after an interrupt.

0x0C

RINTTMP

Word

Temporary location for holding the receive interrupt queue entry, used by the CP

(reserved)

0x10

DATA0

Word

Temporary location for holding data, used by the CP (reserved)

0x14

DATA1

Word

Temporary location for holding data, used by the CP (reserved)

0x18

TINTBASE

Word

Multi-channel transmitter circular interrupt table base address. The interrupt circular

table is a cyclic table (FIFO-like). Each table entry contains information about an

interrupt request generated by the MCC to the host.

0x1C

TINTPTR

Word

Pointer to the transmitter circular interrupt table. The CP writes the next interrupt

information to this entry when an exception occurs. The user must copy the

TINTBASE value to TINTPTR before enabling interrupts. Further updates of the

TINTPTR are done by the CP.

0x20

TINTTMP

Word

Temporary location for holding the transmit interrupt queue entry, used by the CP. The

60x initializes this field before initializing the MCC. The user must clear it before

enabling interrupts.

0x24

SCTPBASE

Hword Internal pointer for the super channel transmit table, offset from the DPRAM address

0x26

—

Hword

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