Deep understanding of ARM architecture ()-Reset

This article prepared by muge0913, reproduced please note the Source: http://blog.csdn.net/muge0913/article/details/7371433

Author: Zhang tonghao, mail: muge0913@sina.com

Reset

Initi6410x has three types ofreset signals and syscon can place the system into one of three resets.

• Hardware reset: It isgenerated by asserting xnreset. It is an uncompromised, ungated, total andcomplete reset that is used when you do not require information in system anymore.
It fully initializes all system.

• Watchdog Reset: It isgenerated by a special hardware block, I. e., watchdog timer. When the system ishanged due to an unpredictable software error, the hardware block monitorsinternal
Hardware status and generates reset signal to escape from this status.

• Wakeup Reset: It is generatedwhen initi6410x wake up from sleep mode. Since internal hardware states are notavailable any more after sleep mode, they must be initialized.

 

Hardwarereset

When the xnreset pin is declared and all units in the system (except RTC) are reset to a pre-defined state, the hardware reset is called. During this period, the following action will occur: all internal registers and arm1176 kernels are in a pre-defined reset state. All pins have their reset status. When xnreset is declared, the xnrstout pin is declared.

Xnreset is not blocked and is always enabled. The declaration of xnreset, regardless of the previous mode

Bit status. Xnrset must be held long enough to allow internal stability and propagation.

 

The hardwarereset is invoked when xnreset pin is asserted and all units in the system (partition t RTC) are reset to pre-defined States. During this period, the followingactions
Occur.

• All internalregisters and arm1176 core go to the pre-defined reset states.

• All pins gettheir reset state.

• Xnrstout pinis asserted when xnreset is asserted.

Xnreset isun-Maskable and is always enabled. Upon assertion of xnreset, initi6410x entersinto reset State regardless of the previous mode. xnrset must be held longenough to allow
Internal Stabilization and propagation of the reset state toenter proper reset state.

Powerregulator for initi6410x must be stable prior to the deassertion of xnreset. Otherwise, it may damage initi6410x and the operation is unpredictable. Figure3-17 is the timing
Digoal of power-on reset and PLL turn-on sequence.

Watchdogreset

When the software is suspended, the watchdog reset is called. Therefore, a timeout command is issued when the watchdog cannot be fed in time. The following actions occur when the watchdog is reset:

All modules except the alive and RTC modules enter the pre-defined reset status. All pins are reset. The nrstout pin is declared during the watchdog reset.

In normal and Idle modes, the watchdog can be activated and generate a timeout signal. When the watchdog timer times out and resets the Enable

Can be called. Therefore, the following occurs in sequence:

1) wdt generates a timeout signal.

2) syscon calls the reset signal to initialize the internal IP address.

3) including nrstout reset declared until the Reset Counter rst_stable is terminated.

Watchdog resetis invoked when a software hang-up. Then, the software Cannot initialize aregister within wdt and wdt makes time-out signals for watchdog reset. As Theoccurrence
Of Watchdog reset means that system has fatal problem, it behaveslike external reset failed t reset Status Register. During the watchdog reset,

Followingactions occur:

• All blocksexcept reset Status Register in alive block go to their pre-defined resetstate.

• All pins gettheir reset state.

• The nrstoutpin is asserted during watchdog reset.

Watchdog resetcan be activated in normal and idle mode, since wdt can generate time-outsignal. It is invoked when watchdog timer and reset are enabled. Then, thefollosequence
Occurs:

1. wdtgenerate time-out signal.

2. sysconinvokes reset signals and initialize internal IPs.

3. The resetincluding nrstout will be asserted until the Reset Counter, rst_stable, isexpired.

 

Wakeupreset

Wakeup reset is invoked wheniniti6410 is woken-up from sleep by a wakeup event. The details are described insleep mode section.