Information

e300 Processor Core Overview
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
7-12 Freescale Semiconductor
7.1.7.2 Time Base/Decrementer
The time base is a 64-bit register (accessed as two 32-bit registers) that is incremented once every four bus
clock cycles; external control of the time base is provided through the time base/decrementer clock base
enable (tben) signal. The decrementer is a 32-bit register that generates a decrementer interrupt after a
programmable delay. The contents of the decrementer register are decremented once every four bus clock
cycles, and the decrementer interrupt is generated as the count passes through zero.
7.1.7.3 JTAG Test and Debug Interface
The core provides JTAG and hardware debug functions for facilitating board testing and chip debugging.
The JTAG test interface (based on IEEE 1149.1) provides a means for boundary-scan testing of the core
and the attached system logic. The hardware debug function accesses the JTAG test port, providing a
means for executing test routines and facilitating chip and software debugging.
All instruction and data address breakpoints are accessible in the IBCR and DBCR. See Section 7.4.8,
“Debug Features,” for more information.
7.1.7.4 Clock Multiplier
The internal clocking of the e300 core is generated from and synchronized to the external clock signal,
sysclk, by means of a voltage-controlled, oscillator-based PLL. The PLL provides programmable internal
processor clock multiplier ratios which multiply the externally supplied clock frequency. The bus clock is
the same frequency and is synchronous with sysclk. The configuration of the PLL can be read by software
from the hardware implementation register 1 (HID1).
7.1.7.5 Core Performance Monitor
The performance monitor provides the ability to count predefined events and processor clocks associated
with particular operations, such as cache misses, mispredicted branches, or the number of cycles an
execution unit stalls. The count of such events can be used to trigger the performance monitor interrupt.
The performance monitor can be used to do the following:
• Improve system performance by monitoring software execution and then recoding algorithms for
more efficiency. For example, memory hierarchy behavior can be monitored and analyzed to
optimize task scheduling or data distribution algorithms.
• Characterize processors in environments not easily characterized by benchmarking.
• Help system developers bring up and debug their systems.
The performance monitor uses the following resources:
• The performance monitor mark bit in the MSR (MSR[PMM]). This bit controls which programs
are monitored.
• The move to/from performance monitor registers (PMR) instructions, mtpmr and mfpmr.
• The external core input, pm_event_in.
•PMRs