GR740-UM-DS, Nov 2017, Version 1.7
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GR740
4.6
PLL watchdog
An additional watchdog is included in the system to detect if the main system clock stops running due
to PLL malfunction or other unforeseen issue. The PLL watchdog is combined with the regular
watchdog (GPTIMER0 timer 5) status and output on the WDOGN open-drain output. The watchdog
has no other effect on the system so if no watchdog functionality is wanted then the WDOGN output
can be ignored.
The PLL watchdog is clocked by the SYS_CLK input clock, and will trigger after 100 million SYS_-
CLK cycles (2.0 seconds at the nominal 50 MHz input frequency) unless it is restarted. It is restarted
whenever the GPTIMER0 TCTRL5 register is written (regardless of value written). Since this register
is written as part of the normal system watchdog handling, the PLL watchdog will not need any addi-
tional handling by software. The timeout value is fixed and can not be reprogrammed, and the current
status of the PLL watchdog is not accessible from software.
4.7
PCI clock
The PCI clock is taken from the MEM_DQM11 signal when the SDRAM is in half-width and PCI
mode is enabled. The device is capable of 33 MHz and 66 MHz operation (TBC). The input signal
PCI_M66EN must reflect the frequency of the input PCI clock. PCI_M66EN should be HIGH if the
PCI clock is a 66 MHz clock and LOW if the PCI clock frequency is 33 MHz.
4.8
MIL-STD-1553B clock
The 20 MHz clock for the MIL-STD-1553B codec is taken from the dedicated pin GR1553_CLK.
4.9
Clock gating unit
The design has a clock gating unit through which individual units can have their AHB clocks enabled/
disabled and resets driven. The peripherals connected to the clock gating unit are listed in the table
below.
The LEON4 processor cores will automatically be clock gated when the processor enters power-down
or halt state. A processor’s floating-point unit (GRFPU) will be clock gated when the corresponding
processor has disabled FPU operations by setting the %psr.ef bit to zero, or when the processor has
entered power-down/halt mode. After reset, processors 1 to 3 will be in power-down mode. Processor
0 will start executing if the BREAK bootstrap signal is LOW. If the BREAK bootstrap signal is HIGH
Table 33.
Devices with gatable clock
Device
State after system reset
Ethernet MAC 0
The Ethernet MACs are gated off after reset unless the Debug Sup-
port Unit is enabled via the DSU_EN signal.
Ethernet MAC 1 is also disabled whenever
mem_ifwidth
is LOW
or PCI mode is enabled (PCIMODE_ENABLE = HIGH)
Ethernet MAC 1
SpaceWire router
The SpaceWire router is disabled after reset unless general purpose
I/O line 11 (GPIO[11]) signals a prom-less system
PCI Target/Initiator and PCI DMA unit
Enabled after reset if PCIMODE_ENABLE=HIGH. Otherwise
disabled.
MIL-STD-1553B interface controller
Disabled after reset
CAN 2.0 controller
Disabled after reset
LEON4 Statistics unit
Disabled after reset
UART 0
Enabled after reset
UART 1
Enabled after reset
SPI controller
Disabled after reset
PROM/IO memory controller
Enabled after reset