This is xnu-8019. See this file in:
/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
#include <machine/machine_routines.h>
#include <pexpert/pexpert.h>
#include <pexpert/protos.h>

/* Local declarations */
void pe_identify_machine(boot_args *args);

/* pe_identify_machine:
 *
 *   Sets up platform parameters.
 *   Returns:    nothing
 */
void
pe_identify_machine(__unused boot_args *args)
{
	// Clear the gPEClockFrequencyInfo struct
	bzero((void *)&gPEClockFrequencyInfo, sizeof(clock_frequency_info_t));

	// Start with default values.
	gPEClockFrequencyInfo.timebase_frequency_hz = 1000000000;
	gPEClockFrequencyInfo.bus_frequency_hz      =  100000000;
	gPEClockFrequencyInfo.cpu_frequency_hz      =  300000000;

	gPEClockFrequencyInfo.bus_frequency_min_hz = gPEClockFrequencyInfo.bus_frequency_hz;
	gPEClockFrequencyInfo.bus_frequency_max_hz = gPEClockFrequencyInfo.bus_frequency_hz;
	gPEClockFrequencyInfo.cpu_frequency_min_hz = gPEClockFrequencyInfo.cpu_frequency_hz;
	gPEClockFrequencyInfo.cpu_frequency_max_hz = gPEClockFrequencyInfo.cpu_frequency_hz;

	gPEClockFrequencyInfo.dec_clock_rate_hz = gPEClockFrequencyInfo.timebase_frequency_hz;
	gPEClockFrequencyInfo.bus_clock_rate_hz = gPEClockFrequencyInfo.bus_frequency_hz;
	gPEClockFrequencyInfo.cpu_clock_rate_hz = gPEClockFrequencyInfo.cpu_frequency_hz;

	// Get real number from some where.

	// Set the num / den pairs form the hz values.
	gPEClockFrequencyInfo.bus_clock_rate_num = gPEClockFrequencyInfo.bus_clock_rate_hz;
	gPEClockFrequencyInfo.bus_clock_rate_den = 1;

	gPEClockFrequencyInfo.bus_to_cpu_rate_num =
	    (2 * gPEClockFrequencyInfo.cpu_clock_rate_hz) / gPEClockFrequencyInfo.bus_clock_rate_hz;
	gPEClockFrequencyInfo.bus_to_cpu_rate_den = 2;

	gPEClockFrequencyInfo.bus_to_dec_rate_num = 1;
	gPEClockFrequencyInfo.bus_to_dec_rate_den =
	    gPEClockFrequencyInfo.bus_clock_rate_hz / gPEClockFrequencyInfo.dec_clock_rate_hz;
}

void
PE_panic_hook(const char *str __unused)
{
}