Register Model
e200z3 Power Architecture Core Reference Manual, Rev. 2
2-32
Freescale Semiconductor
for the system and are enabled by setting HID0[TBEN]. The decrementer (DEC) updates at the same
frequency, which is selected in HID0[SEL_TBCLK]. TB is a volatile resource and must be initialized
during start-up. For details, see
Section 2.11, “Timer Registers.”
The TB is interpreted as a 64-bit unsigned integer that is periodically incremented. Each increment adds 1
to the least-significant bit. The frequency at which the integer is updated is implementation-dependent.
TBL increments until its value becomes 0xFFFF_FFFF (2
32
– 1). At the next increment, its value becomes
0x0000_0000 and TBU is incremented. This process continues until the TBU value becomes
0xFFFF_FFFF and the TBL value becomes 0xFFFF_FFFF (TB is interpreted as
0xFFFF_FFFF_FFFF_FFFF (2
64
– 1)). At the next increment, the TBU value becomes 0x0000_0000 and
the TBL value becomes 0x0000_0000. There is no interrupt (or any other indication).
The period depends on the driving frequency. For example, if TB is driven by 100 MHz divided by 32, the
TB period is as follows:
The TB is implemented to satisfy the following requirements:
•
Loading a GPR from the TB has no effect on the accuracy of the TB.
•
Storing a GPR to the TB replaces the value in the TB with the value in the GPR.
Book E does not specify a relationship between the TB update frequency and other frequencies, such as
the CPU clock or bus clock. The TB update frequency does not have to be constant. One of the following
is required to ensure that system software can keep time of day and operate interval timers:
•
The system provides an (implementation-dependent) interrupt to software when the update
frequency of the TB changes and a way to determine the current update frequency.
•
The update frequency of the TB is under the control of system software.
NOTE
Disabling the TB or making reading the time base privileged prevents the
TB from being used to implement a covert channel in a secure system. If the
operating system initializes the TB on power-on to some reasonable value
and the update frequency of the TB is constant, the TB can be used as a
source of values that increase at a constant rate, such as for time stamps in
trace entries.
32
63 32
63
Field
TBU
TBL
Reset
Undefined on
m_por assertion, unchanged on
p_reset_b
assertion
Undefined on
m_por assertion, unchanged on
p_reset_b
assertion
R/W
User read/Supervisor write
User read/Supervisor write
SPR
269 Read/285 Write
268 Read/284 Write
Figure 2-26. Time Base Upper/Lower Registers (TBU/TBL)
(approximately 187,000 years)
Содержание e200z3
Страница 1: ...e200z3 Power Architecture Core Reference Manual Supports e200z3 e200z335 e200z3coreRM Rev 2 06 2008 ...
Страница 32: ...e200z3 Power Architecture Core Reference Manual Rev 2 xii Freescale Semiconductor ...
Страница 50: ...Register Model e200z3 Power Architecture Core Reference Manual Rev 2 2 2 Freescale Semiconductor ...
Страница 238: ...Memory Management Unit e200z3 Power Architecture Core Reference Manual Rev 2 5 16 Freescale Semiconductor ...
Страница 332: ...Power Management e200z3 Power Architecture Core Reference Manual Rev 2 8 4 Freescale Semiconductor ...
Страница 424: ...Revision History e200z3 Power Architecture Core Reference Manual Rev 2 A 2 Freescale Semiconductor ...