在Main函数之前发生的事 - ZEDBOARD,ZYNQ-7000

What happened before running into main function on zedboard?

Use the zedboard hardware platform to create a Xilinx project and named it print_demo as shown following:

Look into the main function, nothing has been done in the init_platform() function.

Where is the uart init invoking in such a complexing hardware driver files?

Under the project explorer view, select the print_demo_bsp>ps7_cortexa9_0>libsrc>standalone_v3_08_a>src>asm_vectors.s

Double click to read the contents of asm_vectors.s:

.section .vectors

_vector_table:

B    _boot

B    Undefined

B    SVCHandler

B    PrefetchAbortHandler

B    DataAbortHandler

NOP    /* Placeholder for address exception vector*/

B    IRQHandler

B    FIQHandler

_vector_table locates the exception entry point, and the cortex a9 processor execute the first sentence B    _boot

New we go to the definition of _boot (boot.S):

/* this initializes the various processor modes */

 

_prestart:

_boot:

#if XPAR_CPU_ID==0

/* only allow cpu0 through */

    mrc    p15,0,r1,c0,c0,5

    and    r1, r1, #0xf

    cmp    r1, #0

    beq    OKToRun

EndlessLoop0:

    wfe

    b    EndlessLoop0

 

#elif XPAR_CPU_ID==1

/* only allow cpu1 through */

    mrc    p15,0,r1,c0,c0,5

    and    r1, r1, #0xf

    cmp    r1, #1

    beq    OKToRun

EndlessLoop1:

    wfe

    b    EndlessLoop1

#endif

 

The label OKToRun located in the same file:

OKToRun:

    /* set VBAR to the _vector_table address in linker script */

    ldr    r0, =vector_base

    mcr    p15, 0, r0, c12, c0, 0

    …    …

    b    _start                /* jump to C startup code */

    and    r0, r0, r0                /* no op */

 

_start label located in the xil_crt0.S :

start:

    bl __cpu_init        /* Initialize the CPU first (BSP provides this) */

    mov    r0, #0

    …    …

    /* Initialize STDOUT */

    bl    Init_Uart

    …    …

    /* Let her rip */

    bl    main

We have noticed that the bsp program run the Init_Uart before going into main function.

The Init_Uart function locates in the uart.c file:

#define UART_BAUDRATE    115200

Buadrate is determined by the macro. Change it to 9600 if 9600 baudrate is desired.

NOTICE: ANY change in those files locate in the bsp project>ps7_cortexa9_0 will be ignored as the contents will regenerate once building the project. If need to re-invode the init_uart function again in the main function to make a change.