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FPGA
MEN Mikro Elektronik GmbH
83
20A014-00 E2 – 2007-08-16
3.2
System Unit
The system unit is available in all configurations and contains a number of modules
with system functionality communicating with the CPU.
3.2.1
Functional Description
3.2.1.1
Interrupt Controller
The interrupt controller combines the interrupt requests of all implemented
modules, one interrupt line for one module. The system registers are consolidated to
one module, therefore interrupt line 0 is reserved for the system register unit. Since
the interrupt controller handles 16 interrupt requests, 15 IP cores can request an
interrupt without sharing.
The PowerPC microcontroller which is used to interact with the FPGA contains an
interrupt controller, so it is not necessary to prioritize the interrupt requests. This is
done by the microcontroller. The interrupt requests are stored in a 16-bit
Interrupt
Request Register (IRQR)
and are periodically sent to the interrupt controller of the
PowerPC through parallel I/O lines. There is one PCI interrupt line for all interrupt
requests. All used interrupt requests are ORed to this interrupt line. Any module's
interrupt request can be enabled or disabled only in the module which generates the
interrupt by writing 1 or 0 to the corresponding bit of the module's interrupt enable
register.
The CPU has to reset an interrupt request in the module which generates the
interrupt.
3.2.1.2
Reset Controller
Since there are several reset possibilities the CPU can read the information which
reset condition occurred the last time. Therefore, the board’s FPGA contains a reset
controller with a reset register which stores the cause of the occurred restart.
A system reset can occur through:
• Reset button
• Internal watchdog timer expiration
• External
HRESET
(e.g. by external watchdog timer expiration)
• Software reset
The reset controller notices the reset cause by watching its reset inputs and stores
the cause in the
Reset Cause Register (RCR)
. This register must not be set back by
the system reset, so that the CPU is able to read the reset cause after system restart
from the board’s FPGA Reset Cause Register. The CPU can reset the bits in the
reset cause register by writing 1 to the corresponding bit.
The reset controller is able to generate an interrupt on a power supply fail indication.
The power fail detection has to be done on the ESM carrier board. The time between
the indication and the failure of 5V/3.3V can be used by the CPU to save the date
and time of exception. This interrupt can be enabled or disabled by handling the
System Unit Control Register (SUCR)
.