/* calibrate.c: default delay calibration * * Excised from init/main.c * Copyright (C) 1991, 1992 Linus Torvalds */ #include <linux/sched.h> #include <linux/delay.h> #include <linux/init.h> static unsigned long preset_lpj; static int __init lpj_setup(char *str) { preset_lpj = simple_strtoul(str,NULL,0); return 1; } __setup("lpj=", lpj_setup); /* * This is the number of bits of precision for the loops_per_jiffy. Each * bit takes on average 1.5/HZ seconds. This (like the original) is a little * better than 1% */ #define LPS_PREC 8 void __devinit calibrate_delay(void) { unsigned long ticks, loopbit; int lps_precision = LPS_PREC; if (preset_lpj) { loops_per_jiffy = preset_lpj; printk("Calibrating delay loop (skipped)... " "%lu.%02lu BogoMIPS preset\n", loops_per_jiffy/(500000/HZ), (loops_per_jiffy/(5000/HZ)) % 100); } else { loops_per_jiffy = (1<<12); printk(KERN_DEBUG "Calibrating delay loop... "); while ((loops_per_jiffy <<= 1) != 0) { /* wait for "start of" clock tick */ ticks = jiffies; while (ticks == jiffies) /* nothing */; /* Go .. */ ticks = jiffies; __delay(loops_per_jiffy); ticks = jiffies - ticks; if (ticks) break; } /* * Do a binary approximation to get loops_per_jiffy set to * equal one clock (up to lps_precision bits) */ loops_per_jiffy >>= 1; loopbit = loops_per_jiffy; while (lps_precision-- && (loopbit >>= 1)) { loops_per_jiffy |= loopbit; ticks = jiffies; while (ticks == jiffies) /* nothing */; ticks = jiffies; __delay(loops_per_jiffy); if (jiffies != ticks) /* longer than 1 tick */ loops_per_jiffy &= ~loopbit; } /* Round the value and print it */ printk("%lu.%02lu BogoMIPS (lpj=%lu)\n", loops_per_jiffy/(500000/HZ), (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy); } }