IoMeter needs a high resolution time source for performance measurement. Under IA32 platform, this is achieved via rdtsc().
Under Intel XScale Microarchitecture like IOP331 and IOP321, there is a 32bit CCNT (cycle counter) available for this purpose. But since it is only 32 bits. It overflows very quickly. So I added an extra counter to record how many times it overflows. Then expand it to a 64bit value.
Instead of adding a new system call to transfer this value to user space program, we create a virtual character device and export this value via ioctl interface.
The device node is created by the ccntmknod script. And user program can access this counter with code piece:
...
#define CCNT_IOC_MAGIC 0xAC
#define CCNT_IOC_GETCCNT _IOR(CCNT_IOC_MAGIC, 1, unsigned long long)
if ((fd = open("/dev/ccnt", O_RDONLY)) < 0) {
printf("device file open fail!\n");
exit(1);
}
if ((res = ioctl(fd, CCNT_IOC_GETCCNT, &x)) >= 0 ) {
printf("%llu\n", x);
}
...
Write to me (mingz@ele.uri.edu) if there are any problem or suggestion. Thanks.