Copyright © Siemens AG 2010. All rights reserved.
Page
66
ERTEC 400 Manual
Technical data subject to change
Version 1.2.2
5.2.2
Watchdog Reset
The watchdog reset involves software monitoring by the hardware. Monitoring is based on a time setting in the
watchdog timer. Retriggering the timer at a specified reload value prevents the watchdog reset from being
triggered. If the timer is not retriggered, the watchdog reset is enabled after the timer expires if the watchdog
function is active with the
WD_RES_FREI
bit. The watchdog reset is controlled in the ERTEC 400 by means of
assignable pulse stretching (PV). The watchdog reset resets the complete ERTEC 400 circuit. The watchdog
event is signaled to the host system via a GPIO pin.
As in the case of a hardware reset, a bit is set in the reset status register. This bit remains unaffected by the
triggered reset function. This register can be evaluated after a restart.
5.2.3
Software reset
A software reset can be triggered in the ERTEC 400 by setting a bit in the reset control register. The
XRES_SOFT
bit is set in the reset status register when the reset is triggered.
5.2.4
PCI bridge reset
A hardware reset of the PCI bridge can be generated using the following functions:
•
Activating hardware reset pins
RES_PCI_N
and
RESET_N
•
Activating the AHB PCI software reset by setting the
XRES_PCI_AHB_SOFT
bit in the reset control
register
The PCI bridge side that is clocked with CLK_PCI (33/66 MHz) resets the
RES_PCI_N
output. The state of
RES_PCI_N
can be read in the reset control register.
The PCI bridge side that is clocked with CLK_50MHz is reset by
XRES_PCI_AHB_SOFT
software resets .
In order to ensure a defined state of the PCI bridge through the reset sources indicated above, you must make
sure that both sides of the PCI bridge are reset. A hardware reset of the PCI bridge clears all bridge and
configuration registers.
To prevent the PCI registers from being cleared, a warm reset is possible for the PCI bridge. This requires that
the
PCI_SOFT_RESREQ
bit be set in the
PCI_RES_REQ
register. The PCI bridge terminates all transactions at
this moment and issues an acknowledgement with
PCI_SOFT_RESACK.
This state can be scanned in the
PCI_RES_ACK register by the ARM946E-S user software. All new transactions from the AHB and PCI bus are
rejected with Retry. This also pertains to the bridge and configuration registers on the AHB side.
The state is retained until the
PCI_SOFT_RESREQ
bit is deleted again. All of the registers indicated above can
be addressed in the system control register area.
5.2.5
Actions when HW Reset is Active
During the active HW reset phase, the states of the 3 boot pins (3) are read in to the
BOOT_REG
register and the
states of the config pins (5) are read in to the
CONFIG_REG
register. After the hardware reset phase, these pins
are available as normal EMIF function pins.