Am5
x
86
®
CPU
Élan™SC520 Microcontroller User’s Manual
7-5
coherency issues, PCI bus master cycles, or GP-DMA controller operations during this
period. Interrupts generated to the Am5
x
86 CPU will be honored only after the Am5
x
86
CPU is operating again.
Once the CPU PLLs have stabilized and the new core frequency has been established,
caching is once again enabled in the same mode as it was prior to the clock speed change.
There are no special requirements by external system hardware or software to support
clock speed switching.
Note: Not all ÉlanSC520 microcontroller devices support all CPU clock rates. The
maximum supported clock rate for a device is indicated by the part number printed on the
package. The clocking circuitry can be programmed to run the device at higher than rated
speeds. However, if an ÉlanSC520 microcontroller is programmed to run at a higher clock
speed than that for which it is rated, then erroneous operation will result and physical
damage to the device may occur.
7.4.4
Interrupts
The Am5
x
86 CPU receives a maskable interrupt from the programmable interrupt controller
(PIC). The Am5
x
86 CPU also supports a non-maskable interrupt (NMI) input that can be
disabled. See Chapter 15, “Programmable Interrupt Controller”, for details of both maskable
and non-maskable interrupt sources and routing.
7.4.5
Latency
The clock speed change is transparent to the system with the exception that there is
approximately a 1-ms delay to allow the Am5
x
86 CPU’s clock PLLs to stabilize. Interrupts
generated to the Am5
x
86 CPU will be honored only after the Am5
x
86 CPU is operating
again.
7.5
INITIALIZATION
The Am5
x
86 CPU included on the ÉlanSC520 microcontroller supports two different types
of CPU reset: hard CPU reset and soft CPU reset. Chapter 6, “Reset Generation” provides
details of the various sources of hard and soft reset to the Am5
x
86 CPU. For additional
information on Am5
x
86 CPU initialization, see Chapter 3, “System Initialization” and the
references provided in “Operation” on page 7-3.
7.5.1
Hard CPU Reset
The Am5
x
86 CPU is reset during a hard CPU reset, and the Am5
x
86 CPU core clock
frequency defaults to 100 MHz. Hard CPU reset is used to initialize the Am5
x
86 CPU due
to deassertion of the PWRGOOD signal, as well as other reset sources (see Table 6-3 on
page 6-4). Hard CPU reset resets Am5
x
86 CPU registers and the internal cache.
Hard CPU reset forces the microprocessor to terminate all execution and local bus activity.
All entries into the cache are invalidated, the cache is disabled, and the FPU is reset. The
Am5
x
86 CPU begins executing from the boot vector at FFFFFFF0h after system reset is
deasserted. The core clock frequency is 100 MHz.
7.5.2
Soft CPU Reset
Soft CPU reset does not affect the CPU’s write buffers, cache, or cache mode (write-back
or write-through). The Am5
x
86 CPU core clock frequency remains the same, and cache
snooping continues unaffected during soft reset.
Soft reset provides a method to switch from protected to real operating mode. After a soft
CPU reset, the Am5
x
86 CPU begins initialization at location FFFFFFF0h. The processor
state is the same as it is after a hard reset, except that the internal cache, the CD and NW
Содержание Elan SC520
Страница 1: ...lan SC520 Microcontroller User s Manual Order 22004A...
Страница 4: ...iv lan SC520 Microcontroller User s Manual...
Страница 28: ...Introduction xxviii lan SC520 Microcontroller User s Manual...
Страница 42: ...Architectural Overview 1 14 lan SC520 Microcontroller User s Manual...
Страница 78: ...System Initialization 3 22 lan SC520 Microcontroller User s Manual...
Страница 108: ...Clock Generation and Control 5 10 lan SC520 Microcontroller User s Manual...
Страница 118: ...Reset Generation 6 10 lan SC520 Microcontroller User s Manual...
Страница 148: ...System Arbitration 8 24 lan SC520 Microcontroller User s Manual...
Страница 214: ...SDRAM Controller 10 36 lan SC520 Microcontroller User s Manual...
Страница 230: ...Write Buffer and Read Buffer 11 16 lan SC520 Microcontroller User s Manual...
Страница 288: ...GP Bus DMA Controller 14 22 lan SC520 Microcontroller User s Manual...
Страница 316: ...Programmable Interval Timer 16 8 lan SC520 Microcontroller User s Manual...
Страница 328: ...Software Timer 18 4 lan SC520 Microcontroller User s Manual...
Страница 346: ...Real Time Clock 20 12 lan SC520 Microcontroller User s Manual...
Страница 360: ...UART Serial Ports 21 14 lan SC520 Microcontroller User s Manual...
Страница 414: ...AMDebug Technology 26 8 lan SC520 Microcontroller User s Manual...