The ppc function used in calibration is __delay. It is located in arch/ppc/kernel/misc.S. It uses instruction bdnz, looping on itself. On 860, it takes 2 cycles per bdnz. On 8260, it takes 3 cycles per bdnz. I guess it is because both CPUs have different pipelines. The result is later multiplied by 2 prior to be displayed, around line 197 in init/main.c. This is why it gives 1BogoMips = 1MHz on 860.
Regards, -------------------------------------------- Jean-Denis Boyer, B.Eng., Technical Leader Mediatrix Telecom Inc. 4229 Garlock Street Sherbrooke (Qu?bec) J1L 2C8 CANADA (819)829-8749 x241 -------------------------------------------- > -----Original Message----- > From: Wojciech Kromer [mailto:krom at dgt-lab.com.pl] > Sent: 24 mars, 2003 02:17 > To: Linuxppc-Embedded (E-mail) > Subject: BogoMIPS on 8xx vs 82xx > > > > On 8xx running 50 MHz gives ~ 50 BogoMIPS, runnig 65 gives > approx 65 and > so on, close to linear... > but on 8250 running core 266Mhz (66 on bus, 133 cpm) i get only > 175BogoMIPS. Why??? ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
