
GR716-DS-UM, May 2019, Version 1.29
56
www.cobham.com/gaisler
GR716
3
Signals
3.1
Bootstrap signals
The power-up and initialisation state is affected by several external signals as shown in table 30.The
bootstrap signals taken via GPIO, DUART and SPIM signals are saved when the on-chip system reset
is released. This occurs after deassertion of the internal power-on-reset or RESET_IN_N input and
valid input clock on the SYS_CLK pin. The state of the signals are sampled and stored in a bootstrap
register. See section 7.2 for boot strap register description.
Note that some pins used for bootstrapping have dual purpose can be used for normal operations after
reset has been released.
Table 30.
Bootstrap signals
Pin
Functional description
DSU_EN
Enables the Debug Support Unit (DSU) and other members connected to the Debug AHB bus. If
DSU_EN is HIGH the DSU and the Debug AHB bus will be clocked. If DSU_EN is LOW the DSU
and all members on the Debug AHB bus will be clock gated off
DSU_BREAK
Puts processor in debug mode when asserted while DSU_EN is HIGH. When DSU_EN is LOW,
BREAK is assigned to the timer enable bit of the watchdog timer and also controls if the processor
starts executing after reset.
GPIO[17]
Enable bypass of internal boot ROM.
Boot strapping this signal 'high' will force the processor NOT to execute the internal boot software.
Normally the processor starts executing from address 0x0. But if this bootstrap is 'high' the processor
will start execute from software from address selected by bootstrap signals SPIM_MOSI & SPIM_SCK
& SPIM_SEL.
GPIO[0]
Determines the use of EDAC for external boot RAM when the GR716 microcontroller shall boot from
external memory. Set to low for enabling EDAC and to high for disabling EDAC.
Determine the use of PLL when the GR716 microcontroller shall boot via a remote source.
GPIO[62]
Enable test of internal memories at startup. The processor starts checking internal memory for bit errors
during boot if this bootstrap is set to 'high'. Setting this to 'high' will slow down the boot processes since
the check is software based.
GPIO[63]
Enables extra protection of external boot source or setting SpaceWire clock frequency
If boot from external RAM/ROM this pin enable the use of redundant memory if primary boot memory
fails.
If remote access via SPW this pin together with DUART_TXD are used to set the SpaceWire default
speed.
DUART_TXD
If boot from external SRAM/ROM/SPI-ROM this pin are used for selecting to copy ASW image from
selected external boot RAM/ROM (If not set for this option. The GR716 microcontroller will start exe-
cute from the selected external memory)
If remote access via SPW is selected this pin together with GPIO[63] are used to set the SPW default
speed. Set DUART_TXD & GPIO[63] accordingly depending on external SpaceWire frequency:
"00" - For 5Mhz external frequency source
"01" - For 10Mhz external frequency source
"10" - For 20Mhz external frequency source
"11" - For 25Mhz external frequency source
SPIM_MOSI
Enable remote access. When remote access is disabled processor will start from selected external boot
memory.