-
Notifications
You must be signed in to change notification settings - Fork 410
Boot Process
The boot process is a bit of madness, but justifiable madness.
The LPC4320 bootloader initializes the Cortex-M4F core to boot from the start of external SPI flash. The M0 core stays in reset. The bootstrap code runs from SPI flash, on the Cortex-M4F. The bootstrap initializes the Cortex-M0 to execute the application code from SPI flash, then sleeps. The application code copies the baseband code into RAM, configures the Cortex-M4F to run from RAM, then resets the Cortex-M4F to begin baseband execution.
(TODO: A diagram would be helpful, showing the M4F and M0 activities vs. time.)
In the PortaPack image, the Cortex-M4F "bootstrap" image is located at the start of SPI flash. It's executed by the LPC4320 built-in bootloader. The M4 clock is already set to 96MHz. The bootstrap code configures SPIFI to run at (approximately) maximum speed. Then, it initializes the Cortex-M0's memory map to point at the "application" image in SPI flash, and releases the Cortex-M0 from reset. The bootstrap then sleeps the Cortex-M4 until the M0 application needs to run baseband firmware on it.
On the Cortex-M0 core, boot time looks like this:
ResetHandler:
Initialize process stack pointer
Initialize stack RAM regions (fill with pattern)
__early_init()
Enable extra processor exceptions for debugging
Init data segment (copy SPI flash -> data region in RAM)
Initialize BSS (fill RAM region with 0)
__late_init()
reset()
Reset most peripherals -- not SCU, SPIFI, or M0APP
halInit()
hal_lld_init()
Init timer 3 as cycle counter (no DWT on M0)
Init RIT as SysTick (no SysTick on M0)
palInit()
gptInit()
i2cInit()
sdcInit()
spiInit()
rtcInit()
boardInit()
chSysInit()
port_init()
_scheduler_init()
_vt_init()
_core_init()
_heap_init()
chSysEnable()
chThdCreateStatic(_idle_thread_wa, ...)
Constructors
main()
Destructors
_default_exit()
while(1);
On the Cortex-M4F core, these are the stages a baseband image moves through:
ResetHandler:
Initialize process stack pointer
Initialize FPU
Initialize stack RAM regions (fill with pattern)
__early_init()
Enable extra processor exceptions for debugging
Init data segment (copy SPI flash -> data region in RAM)
Initialize BSS (fill RAM region with 0)
__late_init()
halInit()
hal_lld_init()
Init SysTick
Init DWT as cycle counter
# Baseband controls no hardware, so no hardware init here.
boardInit()
chSysInit()
port_init()
_scheduler_init()
_vt_init()
_core_init()
_heap_init()
chSysEnable()
chThdCreateStatic(_idle_thread_wa, ...)
Constructors
main()
Destructors
_default_exit()
while(1);