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GR716-DS-UM, May 2019, Version 1.29
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GR716
counter will be saved in the Interrupt Acknowledge Timestamp Register. The difference between the
Interrupt Assertion timestamp and the Interrupt Acknowledge timestamp is the number of system
clock cycles that was required for the processor to react to the interrupt and divert execution to the
trap handler.
2.2.4
Reset and software boot
The reset default behavior for all included cores, except the LEON3FT processor, is to enter an idle
state upon reset. The internal reset signal will be asserted as a result of power-on. In the idle state the
cores do not initiate any transactions nor keep any output signals in an idle state. This is of particular
concern for bidirectional signals to prevent contention.
The LEON3FT processor will normally start executing from a predefined start address 0x0000000 at
reset. The start of execution can be prevented by assertion of an external break signal. If the break sig-
nal is asserted then the processor will enter power-down mode after reset. This will allow software
upload from an external entity that can then start the processor at a dynamically specified address, by
writing to the interrupt controller's register interface. Processor can optionally be forced via boot-
straps to be forced to start from external PROM, SRAM, MRAM, SPI or I2C memory. This mode
could be used if the application requires separate boot code than the one existing in the LEON3FT
microcontroller boot ROM. Boot addresses for external PROM and SPI memory are defined in sec-
tion 2.11.
A boot ROM application is placed at address 0x00000000 and is normally executed after reset. The
boot application supports system functions controllability via external bootstrap registers. The appli-
cation always starts executing after reset and checking the value of external bootstrap signals. Based
on these signals the processor performs tasks such as load software to internal RAM from an external
memory device, enable remote access via SpaceWire, SPI, UART or I2C. See section 3.1 for more
information about bootstrap options for the boot ROM.
In the case of boot from I2C, the boot ROM application will copy the content of the I2C into the on-
board memory and start to execute the software setup by application.
A protocol to guard against the system trying to boot using a corrupt boot image is implemented using
a protected image format containing an image header, boot code, data checksum and header check-
sum, see section 51. Extra protection can be enabled via bootstraps by reading identical images from
redundant memories but needs to be configured before booting via an external boot strap.
Self-test and diagnostic test of the CPU and internal RAMs can be enabled via bootstraps. The inter-
nal ROM will check for Stuck-At and Transition errors in local instruction and data ram. Stuck-At or
Transition error(s) will result an error reported in the boot report, see 51.2.5.
2.2.5
Direct boot from external memory
Custom boot options are supported via bootstrap options to bypass the internal boot ROM code. The
LEON3FT microcontroller can be configured to boot directly from external ROM, external SRAM,
external SPI Memory or internal NVRAM in package (GR716 with internal NVRAM is currently not
available).
2.2.6
Atomic access
The microcontroller supports atomic bit and bit field access for all APB peripherals and in internal
data memory when accessed from the LEON3FT processor. The atomic access is supported via
address mirrors of the peripheral and local data ram. The microcontroller supports the following
atomic operations:
•
Configuration register will 'or' data written from processor with contents of control register
•
Configuration register will 'and' data written from processor with contents of control register
•
Configuration register will 'xor' data written from processor with contents of control register