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in memory management of transmit and receive data frames. External memory (DRAM) is inexpensive, and because BD rings in external memory have no inherent size limitations, memory management easily can be optimized to system needs.

1.4.2 SIU Interrupt ConÞguration

As shown in Figure 1-2, the SIU receives interrupts from internal sources, such as the FEC and other modules and external pins, IRQ[0Ð7].

System Interface Unit

SWT

 

 

 

 

 

 

 

 

 

NMI

 

 

 

 

GEN

 

IRQ[0Ð7]

Edge

 

IRQ0

 

 

 

 

.

Detector

 

 

 

.

Selector

 

 

 

.

 

 

NMI

 

 

 

Inc

 

 

 

DEC

Level 7

 

DEC

 

 

Semiconductor,

 

ControllerInterrupt

 

TB

Level 6

 

 

 

 

 

 

 

 

 

 

 

 

PowerPC

 

PIT

Level 5

 

Core

 

 

 

 

RTC

Level 4

 

 

 

 

 

 

 

 

 

 

IREQ

 

 

Level 3

 

 

 

PCMCIA

 

 

 

 

 

Level 2

 

 

Freescale

CPM Interrupt

 

 

 

Controller

Level 1

 

 

 

 

 

 

FEC

Level 0

 

 

 

 

 

 

 

Debug

 

 

Debug

 

 

 

 

 

Figure 1-2. MPC860T Interrupt Structure

 

Note that MII_TXCLK is shared with IRQ7 and becomes active as soon as the ETHER_EN bit in the Ethernet control register (ECNTRL) is set. IRQ7 must be masked in the system interface unit (SIU).

1.5 Glueless System Design

A fundamental design goal of the MPC8xx family was ease of interface to other system components. Examples of system design are located in the MPC860T userÕs manual.

MOTOROLAChapter 1.Overview1-5

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Freescale Semiconductor MPC860T user manual Glueless System Design, SIU Interrupt ConÞguration