Related Information
HPS State on Entry to the Preloader
on page 30-11
L4 Watchdog 0 Timer
The L4 watchdog 0 timer is reserved for boot ROM use. While booting, if a watchdog reset happens before
software control passes to the preloader, boot ROM code attempts to load the last valid preloader image,
identified by the
initswlastld
register in the
romcodegrp
group in the system manager.
If the watchdog reset happens after the preloader has started executing but before the preloader writes a
valid value to
initswstate
register, the boot ROM increments
initswlastld
and attempts to load
that image. If the watchdog reset happens after the preloader writes a valid value to
initswstate
register,
boot ROM code attempts to load the image indicated by
initswlastld
register.
HPS State on Entry to the Preloader
When the boot ROM code is ready to pass control to the preloader, the processor (CPU0) is in the following
state:
• Instruction cache is enabled
• Branch predictor is enabled
• Data cache is disabled
• MMU is disabled
• Floating point unit is enabled
• NEON vector unit is enabled
• Processor is in ARM secure supervisor mode
The boot ROM code sets the ARM
®
Cortex
™
-A9 MPCore
™
registers to the following values:
• r0—contains the pointer to the shared memory block, which is used to pass information from the boot
ROM code to the preloader. The shared memory block is located in the top 4 KB of on-chip RAM.
• r1—contains the length of the shared memory.
• r2—unused and set to 0x0.
• r3—reserved.
All other MPCore registers are undefined.
When booting CPU0 using the FPGA boot, or when booting CPU1 using any boot source, all MPCore
registers, caches, the MMU, the floating point unit, and the NEON vector unit are undefined. HPS
subsystems and the PLLs are undefined.
Note:
When the boot ROM code passes control to the preloader, the following conditions also exist:
• The boot ROM is still mapped to address 0x0.
• The L4 watchdog 0 timer is active and has been toggled.
Altera Corporation
Booting and Configuration Introduction
A-11
L4 Watchdog 0 Timer
cv_5400a
2013.12.30