System Test and Debugging
24-12
Élan™SC520 Microcontroller User’s Manual
■
The Am5
x
86 CPU’s internal cache can greatly affect system performance.
– When disabled, all Am5
x
86 CPU operations require an external bus cycle, which yields
significantly less bus bandwidth for PCI bus masters and GP-DMA initiators.
– When configured in write-through cache mode, all Am5
x
86 CPU write cycles are
forwarded to the Am5
x
86 CPU bus, whereas in write-back cache mode, they are only
forwarded out of the Am5
x
86 CPU when a cache miss or write-back/copy-back cycle
occurs. Although write-through cache mode takes much less of the bandwidth away
from PCI bus masters and GP-DMA initiators, it is significantly more than when the
cache is operating in write-back mode.
– When areas of memory are marked as noncacheable in the PAR registers, the
overhead of cache write-backs is reduced, yielding lower latency for all system bus
owners.
■
The internal Am5
x
86 CPU core clock speed affects overall Am5
x
86 CPU performance
when the Am5
x
86 CPU is able to execute from its internal cache. When the cache is
disabled, the effect of a higher core speed is much less, because all operations require
an external bus cycle at the fixed bus speed of 33 MHz.
■
Disabling the write buffer and read buffer may significantly affect performance,
depending on the ordering of reads and writes, and the number of PCI bus masters and
the amount of GP-DMA activity in the system. It is difficult to predict the exact effect of
these buffers on each system, because there are many dependencies. However, it
should be noted that, in some cases, a notable change in system performance will occur.
This also complicates the system debugging process, because the system bus activity
profile may be much different in the two cases.
■
Enabling interrupts for write-protect violation notification (as with all maskable interrupts),
causes a context switch to occur, which naturally imposes a reload of the Interrupt
Descriptor Table and saving the current state of the Am5
x
86 CPU before servicing the
interrupt. This should not be a long-term problem, because it is expected that the write
violation protection would occur only during the initial debugging phases of system
development.
■
When GP bus echoing is enabled, the access times of the integrated peripherals is
subject to the timing programmed for the external GP bus.
24.5
INITIALIZATION
The state of the ÉlanSC520 microcontroller debugging features after system reset is:
■
The WBMSTR2
±
WBMSTR0 pins default to system test mode, in which they assume the
function of CF_DRAM, DATASTRB, and CF_ROM_GPCS pins respectively.
■
The system arbitration defaults to nonconcurrent arbitration mode operation.
■
Echoing of integrated peripheral accesses is disabled.
■
The Am5
x
86 CPU’s cache is disabled and configured for write-back cache mode.
■
The Am5
x
86 CPU default clock speed is 100 MHz.
■
The write buffer and the read buffer are disabled.
■
The write-protection violation interrupt is disabled, and the Programmable Address
Region (PAR) registers are cleared; thus, no write-protect or non-executable memory
regions are defined.
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...