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Correct ARM Versatile Timer Initialization 

- According to ARM Dual-Timer Module (SP804) TRM (ARM DDI0271),
   -- Timer Value Register @ TIMER Base + 4 is Read-only.
   -- Prescale Value (Bits 3-2 of TIMER Control register)
	can only be one of 00,01,10. 11 is undefined.
   -- CFG_HZ for Versatile board is set to
	#define CFG_HZ		(1000000 / 256)
	So Prescale bits is set to indicate
	- 8 Stages of Prescale, Clock divided by 256
 - The Timer Control Register has one Undefined/Shouldn't Use Bit
   So we should do read/modify/write Operation

Signed-off-by: Gururaja Hebbar <gururajakr@sanyo.co.in>
This commit is contained in:
Gururaja Hebbar K R 2008-08-25 11:11:34 +02:00 committed by Jean-Christophe PLAGNIOL-VILLARD
parent 535cfa4f3d
commit e8f1207bbf
1 changed files with 35 additions and 4 deletions
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39
cpu/arm926ejs/versatile/timer.c Normal file → Executable file
View File

@ -46,12 +46,43 @@
static ulong timestamp;
static ulong lastdec;
/* nothing really to do with interrupts, just starts up a counter. */
#define TIMER_ENABLE (1 << 7)
#define TIMER_MODE_MSK (1 << 6)
#define TIMER_MODE_FR (0 << 6)
#define TIMER_MODE_PD (1 << 6)
#define TIMER_INT_EN (1 << 5)
#define TIMER_PRS_MSK (3 << 2)
#define TIMER_PRS_8S (1 << 3)
#define TIMER_SIZE_MSK (1 << 2)
#define TIMER_ONE_SHT (1 << 0)
int timer_init (void)
{
*(volatile ulong *)(CFG_TIMERBASE + 0) = CFG_TIMER_RELOAD; /* TimerLoad */
*(volatile ulong *)(CFG_TIMERBASE + 4) = CFG_TIMER_RELOAD; /* TimerValue */
*(volatile ulong *)(CFG_TIMERBASE + 8) = 0x8C;
ulong tmr_ctrl_val;
/* 1st disable the Timer */
tmr_ctrl_val = *(volatile ulong *)(CFG_TIMERBASE + 8);
tmr_ctrl_val &= ~TIMER_ENABLE;
*(volatile ulong *)(CFG_TIMERBASE + 8) = tmr_ctrl_val;
/*
* The Timer Control Register has one Undefined/Shouldn't Use Bit
* So we should do read/modify/write Operation
*/
/*
* Timer Mode : Free Running
* Interrupt : Disabled
* Prescale : 8 Stage, Clk/256
* Tmr Siz : 16 Bit Counter
* Tmr in Wrapping Mode
*/
tmr_ctrl_val = *(volatile ulong *)(CFG_TIMERBASE + 8);
tmr_ctrl_val &= ~(TIMER_MODE_MSK | TIMER_INT_EN | TIMER_PRS_MSK | TIMER_SIZE_MSK | TIMER_ONE_SHT );
tmr_ctrl_val |= (TIMER_ENABLE | TIMER_PRS_8S);
*(volatile ulong *)(CFG_TIMERBASE + 8) = tmr_ctrl_val;
/* init the timestamp and lastdec value */
reset_timer_masked();