hi all:
thanks for your kind help :)
2011/1/17 Winfred Lu <winfred.lu@xxxxxxxxx>:
> 2011/1/16 loody <miloody@xxxxxxxxx>
>>
>> below is the formula about calculating the delay
>> (us * 0x000010c7 * HZ * lpj )) >> 32)
>> I cannot figure out why we need to multiply 0x10c7, and what lpj mean?
>
> 0x10c7 is the rounded up value of (2 ^ 32) / 1,000,000.
>
> The 1,000,000 comes from that 1 second is equal to 1,000,000 micro seconds.
> That the value multiplied by (2 ^ 32) and shifted 32 bit right after is
> equal to
> that the value multiplied by 1.
I found my kernel will compile udelay(xx) as zero no matter what xx I filled in.
below are the dis-assemblies:
(as you can see the v0 = v1 = zero.)
My version is 2.6.30.9:
void __udelay(unsigned long us)
{
unsigned int lpj = current_cpu_data.udelay_val;
__delay(((unsigned long long)(us * 0x000010c7 * HZ * lpj)) >> 32);
80306ed0: 00001821 move v1,zero
80306ed4: 00601021 move v0,v1
#include <asm/compiler.h>
#include <asm/war.h>
inline void __delay(unsigned int loops)
{
__asm__ __volatile__ (
80306ed8: 1440ffff bnez v0,80306ed8 <__udelay+0x8>
80306edc: 2442ffff addiu v0,v0,-1
void __udelay(unsigned long us)
I have double checked the __delay source code of 2.6.33.4
and the dis-assemblies:
void __udelay(unsigned long us)
{
unsigned int lpj = current_cpu_data.udelay_val;
__delay((us * 0x000010c7ull * HZ * lpj) >> 32);
802f7310: 3c02804f lui v0,0x804f
802f7314: 8c429360 lw v0,-27808(v0)
802f7318: 3c050010 lui a1,0x10
802f731c: 34a56256 ori a1,a1,0x6256
802f7320: 00450019 multu v0,a1
802f7324: 00002821 move a1,zero
802f7328: 00001012 mflo v0
802f732c: 00001810 mfhi v1
802f7330: 00a20018 mult a1,v0
802f7334: 70640000 madd v1,a0
802f7338: 00003012 mflo a2
802f733c: 00440019 multu v0,a0
802f7340: 00001810 mfhi v1
802f7344: 00c31021 addu v0,a2,v1
#include <asm/compiler.h>
#include <asm/war.h>
inline void __delay(unsigned int loops)
{
__asm__ __volatile__ (
802f7348: 1440ffff bnez v0,802f7348 <__udelay+0x38>
802f734c: 2442ffff addiu v0,v0,-1
void __udelay(unsigned long us)
{
unsigned int lpj = current_cpu_data.udelay_val;
__delay((us * 0x000010c7ull * HZ * lpj) >> 32);
}
802f7350: 03e00008 jr ra
Does that mean "unsigned long long" not workable?
appreciate your help,
miloody
