G E N M o d u l e

Bits

Access

Mnemonic

Reset

Description

 

 

 

 

 

D18

R/W

BME

0

Bus monitor enable

 

 

 

 

0 Disable bus monitor operation

 

 

 

 

1 Enable bus monitor operation

 

 

 

 

Required to avoid a system lockup condition that

 

 

 

 

can occur when a bus master tries to address

 

 

 

 

memory space that is not decoded by any

 

 

 

 

peripheral.

 

 

 

 

The bus monitor timer detects when a bus master

 

 

 

 

is accessing a peripheral and there is no transfer

 

 

 

 

acknowledge (TA_) response. When the bus

 

 

 

 

monitor timer expires, the current bus cycle is

 

 

 

 

terminated immediately and the current system

 

 

 

 

bus master is issued a data abort indicator.

 

 

 

 

 

D17:16

R/W

BMT

0

Bus monitor timer

 

 

 

 

Controls the timeout period for the bus monitor

 

 

 

 

timer:

 

 

 

 

00 128 BCLKs (bus clocks)

 

 

 

 

01

64 BCLKS

 

 

 

 

10

32 BCLKS

 

 

 

 

11

16 BCLKS

 

 

 

 

The BMT field generally is set to its maximum

 

 

 

 

value, but can be set to a lower value to minimize

 

 

 

 

the latency when issuing a data abort signal. The

 

 

 

 

BMT field needs to be set to a value that is larger

 

 

 

 

than the anticipated longest access time for all

 

 

 

 

peripherals.

 

 

 

 

 

D15

R/W

USER

0

Enable access to internal chip registers in CPU

 

 

 

 

user mode

Controls whether applications operating in ARM user mode (rather than supervisor mode) can access internal registers within the NS7520.

If set to 0, and an application, operating in ARM user mode tries to access (read or write) an internal NS7520 register, the application receives a data abort. This causes a transfer in control to the data abort handler.

If set to 1, any application can access the NS7520 internal registers.

Table 24: System Control register bit definition

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Image 79
Digi NS7520 manual Bus monitor enable, Enable access to internal chip registers in CPU, User mode