I would like to run my program from the SRAM region of the device.
It seemed quite clear to me, that I have to perform following steps:
Modify the vector table offset register SCB->VTOR (located at 0xE000ED08) to point to the beginning of the SRAM region, as that is where my vector table is located: 0x20000000
Reset the device so it fetches the stack pointer initialization value and the reset handler adress again.
Unfortunately, whenever I issue a reset init command in OpenOCD, the value of SCB->VTOR gets cleared. Hence, stack pointer initialization value and reset handler adress are fetched from 0x00000000 instead of 0x20000000.
Question
How do I get my STM32F4 to fetch the vector table from 0x20000000?
Just load the SP (MSP) from 0x20000000 (=VTOR) and the PC from 0x20000004 (=VTOR+4) manually.
The reset init command will usually reset the whole chip and no just the core - and VTOR will be initialized to zero even then.
Related
I am trying to use the USB Device library on STM32Cube but when I execute using the debugger or that I try to turn an LED on in CDC_Receive_FS, it never reaches that point.
Here is how I set up everyting:
My board is a NUCLEO-F746ZG
I enabled USB_OTG_FS in Device_Only mode, activated _VBUS and _SOF. Left everything else by default and USB On The Go FS global interrupt is enabled!
I set up USB_DEVICE: Class For FS IP set to Virtual Port Com, left everything by default
Main loop left empty
CDC_Receive_FS: put breakpoint in it and/or HAL_GPIO_WritePin(LD1_GPIO_Port, LD1_Pin, GPIO_PIN_SET);
I have TIM2 set up for the things I would like to do when it will work
Then I tried to send data to the board, first using Python using serial with a baudrate of 921600 but got nothing. Then using PuTTY with a baudrate of 9600, still nothing...
If anyone has a clue, I have been struggling with it the whole day.
Here is the whole project: https://ecloud.global/s/cjGYqK6z9g58Lm4
The example Reset Handler code provided by STMicro for STM32 (in my case it is for STM32H753) is the following:
Reset_Handler:
ldr sp, =_estack
movs r1, #0
b LoopCopyDataInit
...
I don't understand the first instruction, that sets the stack pointer.
Indeed the Vector Table is defined as follows:
This means that the Stack Pointer is set by the CPU from the first word in the Vector Table. This is confirmed by debug (when breaking before executing the very first instruction of the Reset Handler, the SP is set properly).
Is there a reason to keep this instruction ldr sp, =_estack in thr Reset Handler ?
The Vector table contains on its first position the initial stack address. But the programmer might want to set another value to it or set up the double stack.
In the linker script you have:
_estack = address ;
and in the very simple startup file:
g_pfnVectors:
.word _estack
.word Reset_Handler
but you can change those values to be different or the ResetHandler is called from the bootloader. Then you need to set the stack pointer to the correct value.
I'm working on project on STM32L152RCT6, where i have to build a mechanism to self update the code from the newly gated file(HEX file).
For that i have implemented such mechanism like boot loader where it checks for the new firmware if there it it has to cross verify and if found valid it has to store on "Application location".
I'm taking following steps.
Boot loader address = 0x08000000
Application address = 0x08008000
Somewhere on specified location it has to check for new file through Boot loader program.
If found valid it has to be copy all the HEX on location(as per the guide).
Than running the application code through jump on that location.
Now problem comes from step 5, all the above steps I've done even storing of data has been done properly(verify in STM32 utility), but when i'm jump to the application code it won't work.
Is there i have to cross check or something i'm missing?
Unlike other ARM controllers that directly jump to address 0 at reset, the Cortex-M series takes the start address from a vector table. If the program is loaded directly (without a bootloader), the vector table is at the start of the binary (loaded or mapped to address 0). First entry at offset 0 is the initial value of the stack pointer, second entry at address 4 is called the reset vector, it contains the address of the first instruction to be executed.
Programs loaded with a bootloader usually preserve this arrangement, and put the vector table at the start of the binary, 0x08008000 in your case. Then the reset vector would be at 0x08008004. But it's your application, you should check where did you put your vector table. Hint: look at the .map file generated by the linker to be sure. If it's indeed at 0x08008000, then you can transfer control to the application reset vector so:
void (*app)(void); // declare a pointer to a function
app = *(void (**)(void))0x08008004; // see below
app(); // invoke the function through the pointer
The complicated cast in the second line converts the physical address to a pointer to a pointer to a function, takes the value pointed to it, which is now a pointer to a function, and assigns it to app.
Then you should manage the switchover to the application vector table. You can do it either in the bootloader or in the application, or divide the steps between them.
Disable all interrupts and stop SysTick. Note that SysTick is not an interrupt, don't call NVIC_DisableIRQ() on it. I'd do this step in the bootloader, so it gets responsible to disable whatever it has enabled.
Assign the new vector table address to SCB->VTOR. Beware that the boilerplate SystemInit() function in system_stm32l1xx.c unconditionally changes SCB->VTOR back to the start of the flash, i.e. to 0x08000000, you should edit it to use the proper offset.
You can load the stack pointer value from the vector table too, but it's tricky to do it properly, and not really necessary, the application can just continue to use the stack that was set up in the bootloader. Just check it to make sure it's reasonable.
Have you changed the application according to the new falsh position?
For example the Vector Table has to be set correctl via
SCB->VTOR = ...
When your bootloader starts the app it has to configure everything back to the reset state as the application may relay on the default reset values. Espessially you need to:
Return values of all hardware registers to its reset values
Switch off all peripheral clocks (do not forget about the SysTick)
Disable all enabled interrupts
Return all clock domains to its reset values.
Set the vector table address
Load the stack pointer from the beginning of the APP vector table.
Call the APP entry point.(vertor table start + 4)
Your app has to be compiled and linked using the custom linker script where the FLASH start point is 0x8008000
for example:
FLASH (rx) : ORIGIN = 0x8000000 + 32K, LENGTH = 512K - 32K
SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET;
where FLASH_BASE's value must be equal to the address of your IROM's value in KEIL
example:
#define FLASH_BASE 0x08004000
Keil configuration
I am trying to understand multitasking in PIC18Fs. I know that program counter is stored in Stack before interrupts and then it returns to the same PC address when interrupt finishes. How can I find the PC value stored in Stack and save it in some register so that I can use it later to return to. ?e.g PC value for Task1,Task2 etc.
I think AN818 Answers my question . SO in a pre-emptive OS, I would save the TOSU,TOSL,TOSH and STKPTR (along with other registers) just before executing ISR and from ISR load TOSU,TOSL,TOSH and STKPTR with new value for the next task. Would welcome any further comment/suggestion/example on this. Thanks
Recently I'm learning about the OS. And I want to write a simple bootloader, which change the real mode to protect mode and then load the simple kernel.
But I can't figure out the entry address problem.
At first I put the bootloader in the first sector of the OS.img(qemu), and then the kernel begin at the second sector.
Here's readelf result of my kernel:
The entry point address is 0x800c.
And the LMA and VMA are below:
A part of the bootloader which read elf-type kernel and then get into the entry(),which is the entry point address.
However, when I disassemble the bootloader, the entry() is below:
Call *0x8018, not *0x800c.
I don't know why this happen.
Could you please help me?
call *0x8018 performs a call to an address that is stored at 0x8018, that's correct since ELFHDR is 0x8000 and offset of e_entry in the header is 0x18.
The real problem is in the way you load segments into memory. Each segment should be loaded at address p_vaddr from file offset p_offset. Notice that in your case p_vaddr is 0x8000, that the same place in memory you loaded elf header to and that's why ELFHDR->e_entry gets overwritten. The easiest solution would be to load elf header at different address.
Source: http://www.skyfree.org/linux/references/ELF_Format.pdf