About watch dog timer limit of CPU (Xscale ->IXP425) How can I set more long time ?

[Bob Zhang <zhanglinbao@gmail.com>]

Hello all , 

    My embeded board hardware configuration is like this :
# cat /proc/cpuinfo
Processor       : XScale-IXP425/IXC1100 rev 1 (v5b)
BogoMIPS        : 266.24
Features        : swp half thumb fastmult edsp 

Hardware        : Intel IXDP425 Development Platform
Revision        : 0000
Serial          : 0000000000000000

Through reading datasheet of ixp4xx ,I know it has own watchdog functions ,
please see attchment :15 Timer 

I find a driver by goole , 
see attachment .


Watchdog timer counter is 32 bit register , its max value is 2<<32 -1 

#define TIMER_FREQ 66000000 /* 66 MHZ timer */
#define TIMER_KEY 0x482e
#define TIMER_MARGIN 60  /* (secs) Default is 1 minute */     
//I want to modify it ,I find its max value is 65

static int ixp425_margin = TIMER_MARGIN; /* in seconds */
static int ixp425wdt_users;
//static int pre_margin;  //IXP425 CPU 's watch dog timer is 32 bit , 
//so I define it to be unsigned int --bob
static unsigned int pre_margin;   
pre_margin = TIMER_FREQ *  TIMER_MARGIN 
*IXP425_OSWT = pre_margin; 

if I need one minutes , 
*IXP425_OSWT = 66000000 * 60 =  396000000  ,not overflow  

if I need two minutes , 
*IXP425_OSWT = 66000000 * 120 = 792000000  ( which has been >  2<<32-1  , overflow 

So I compute the max time I can set :
 T_max = 2<<32-1 / 66000000    =  65 seconds ¡£  


--------------------
My question:

if need more seconds ( for example , 5 minutes ) ,what should I do ? 

I have a method based on datasheet (ixp4xx) ,but I don't know if it will successed when system crash 

How can I do to break the limit of hardware ? 
Thanks ahead ! 

--
Best Regards
bob