Reset.s – The first code executed Assembly only –No stacks –No variables, other than scratch registers –Very low level ARM code First code executed in Flash is a patch! –Special code for the development board –Vector table is restored later in the code
Reset.s (continued) __entry: LDR R0, =MEM_MMCR LDR R2, [R0] LDR R1, =MEM_MMCR_m2 AND R2, R2, R1 STR R2, [R0] LDR pc, NA_MAIN # Jump to NET+ARM startup.data.w __vectors.data.w 0 This code resides in ROM at address zero It runs and then jumps to NA_MAIN, the real reset vector
Init.s The real initialization code Start at Reset_Handler_Rom –Jump to Reset_Handler if debugger is detected CS0 valid bit is ‘off’ (set to zero) REFCNT has been set in MMCR (for DRAM) ROM already mapped to higher address –If no debugger, then remap ROM & RAM ROM mapped to 0x0200 0000 RAM mapped to 0x0
Init.s (continued) A Software reset is performed –Only resets EFE, DMA, GEN, SER modules Except BSPEED, BCLKD, & PORT A,B,C Then configure Chip Select Zero –Set base address register –Set option register –Values are OR-ed in to preserve bits already set
Init.s (continued) Then auto-configure CS1 for RAM –Same debugger check is made (again) –SDRAM is assumed and checked –Eventually get to cs1_configured Much of this auto-detect logic can be removed Set up an 8K temporary stack at location 8K –Now we can call our first C routine –Branch with Link so we can return
Ncc_init.c First C routine –Still linear main() style C (pre ThreadX) One line at a time, no multi-tasking First Step, Configure the GEN module –Set System Configuration Register (SCR) Set BSPEED to full speed Turn on Bus Monitor Timer Enable access to NET+ARM internal registers when in USER mode –OR in these settings to preserve earlier settings
Ncc_init.c (continued) Disable Interrupts –(*NCC_GEN).i_er.reg = 0; Use the Interrupt Enable Register Mask Set PLLCNT in PLL Config Register –(*NCC_GEN).pllcr.bits.pllcnt = 6; This value is critical to generate Fsysclk & Fxtal regardless of crystal or oscillator clock input Note that SW does not care about PLL, only about Fsysclk and Fxtal
Ncc_init.c (continued) Initialize the PORT A, B, and C registers –Sets up Serial ports, DMA handshake special signals, and GPIO pins for LEDs on dev board –Port C config leaves the Green LED ‘on’ LED assertions are negative ( 0 == ‘on’) Configure Chip Select 1 for RAM –Being careful to check for a debugger before overwriting settings
Ncc_init.c (continued) Configure Chip Select 3 for NVRAM –Dev Board has 8K parallel EE on CS3 *Very* useful for configuration parameters et. al. Warning, if APP_USE_NVRAM is not set in appconf.h, then CS3 is shut off! –This may cause trouble when integrating new prototype hardware
Ncc_init.c (continued) CS4 is disabled (unused on dev board) –This may cause trouble when integrating new prototype hardware Any memory registers are volatile as long as the USER bit is set in the SCR –You can reconfigure CS4 later in the code! Final Step – a complete RAM test is done –This is what takes 40 seconds to finish bootup Then return right where we left off in init.s
Back to init.s RAM (and other chip selects) are done Setup real running stacks for each operating mode of the ARM7 –ABT, IRQ, FIQ, UND, SVC, USER –Continue running in SYS mode Now use real stacks and jump to romstart
Romstart.c Step one – copy the vector table from ROM to RAM Step Two – copy initialized data from ROM to RAM (.data segment) Step Three – copy uninitialized data from ROM to RAM and set it to zero (.BSS segment)
Romstart.c (cont.) Initialize IRQ tables Reset MII (if used) Perform POST tests (if called out in appconf.h) Re-initialize the IRQ tables –Primarily to restore any changes made during POST tests Return to init.s
Back to init.s (again) Load Stack pointer and PC for ThreadX launch and GO LDR sp, STACK LDR pc, START START is beginning of GHS initialization GHS routine returns after it initializes and calls main() from bsproot.c
main() Everyone’s favorite function, it calls… –setupVectorTable() which writes the real vector table to RAM –NABoardInit() which finishes the specific development board initialization –First level Device Driver Initialization –Finally calls tx_kernel_enter which then turns control over to the ThreadX kernel and automatically calls tx_application_define
The Root Thread In tx_application_define ccode = tx_thread_create (&rootThread, "Root Thread", netosStartup, 0, first_unused_memory, APP_ROOT_STACK_SIZE, APP_ROOT_PRIORITY, 1, TX_AUTO_START);
netosStartup Loads Device Drivers Runs the serial console dialog menu Redirects stdio if so configured Loads and starts the TCP/IP stack Calls applicationStart() to start the user’s program.
BSP Init Summary Init.s – contains most all initialization code ncc_init() – called from init.s romstart() – called from init.s START calls GHS initialization routines tx_application_define – starts ThreadX kernel See BSP Porting Guide for more details.
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