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.