Hi there. I have coded my own bootloader and i need to assign the loaded applications main function and a variable to a specific address that my bootloader calls. Is there a way to force the linker/compiler to place a variable or function at a specific memory address by using the __attribute__ command in my c code. I know that : __attribute__ ((section (".my_mem_name.rwdata"))); assigns the varable or function to a specific memory section, but not a memory specific address. And I have jet another question My bootloader app is placed in internal memory so it executes every time I reset the nois, then it loads a user app into sdram. This works fine but when I jump to "entry" (as defined in the objdump file) nothing happens. If I jump to "main" it seems to work and starts the user program, but if I do this, the user program still uses the exceptions table, heap and stack asignments from the bootloader app. How do I init the assignments from user program? Hopes this makes sense to someone.

Hi Rasdan, > Is there a way to force the linker/compiler to place a variable or function at a > specific memory address by using the __attribute__ command in my c code. This is _normally_ done with the linker command file. For example, a function with a section attribute of ".startfn" in the file start.c can be placed in whatever section you want. If you identify the object file and the input section name as the first entry, it will be located at the start of the output section: <div class='quotetop'>QUOTE </div> --- Quote Start --- SECTIONS { .whatever : { start.o (.startfn) *(.whatever) } ...[/b] --- Quote End --- Everything else from start.o (all other input sections) will be located to their associated output sections as normal. Regards, --Scott

Hi Scott, As i understand you are telling me that i need to make a costum linker script(or edit) generated.x file (the auto linker script). Find the section where i want to place my function eq .text and insert "start.o (.startfn)" before anything else. will look something like this SECTIONS { .text : { start.o (.startfn) "line added" *(.interp) *(.hash) *(.dynsym) *(.dynstr) *(.gnu.version) } right ? the result will be that my function is placed (if .text is defined in sdram) at SDRAMbase+.textoffset (the start of text section in sdram). Do you have any clue about my bootloader jmp question? thx for all your help

Hi Rasdan, > the result will be that my function is placed (if .text is defined in sdram) at > SDRAMbase+.textoffset (the start of text section in sdram). Yes, in the example you provide, your function (if it&#39;s the only .startfn input section in start.o) will be placed at the start of the output .text section. > Do you have any clue about my bootloader jmp question? You&#39;ll need to provide more details ... but it&#39;s probably a problem with your app format, your loader, or your startup code. > My bootloader app is placed in internal memory so it executes every time I reset the > nois, then it loads a user app into sdram. This works fine but when I jump to "entry" > (as defined in the objdump file) nothing happens. What do you mean "it loads a user app"? Are you using an instruction cache and do you flush before jumping? What code did you implement at the entry point? What happens when you download the code (e.g. using nios2-download) ... does it work? Use nios2-console and set a breakpoint just before jumping to your code. Then step through ... see what happens. Regards, --Scott

Hi Scott, >You&#39;ll need to provide more details ... but it&#39;s probably a problem with your >app format, your loader, or your startup code. Ok here is the detail: I’m coding a standalone bootloader for use with custom fpga hardware. The fpga includes a nios with instruction cache. On this hardware there is also a PowerPC (not in the fpga). The setup should work as follows: In the fpga, at power on, a fpgaimage is loaded from the PowerPC. This image includes a nios and the bootloader code. Bootloader code is placed in internal fpga memory when I build the quartus project. The PowerPC resets the niosCPU and the bootloader starts. The bootloader app requests a binary file from the PowerPC. The file is loaded, by the nios bootloader, into SDRAM. All this works perfect. The last thing the bootloader has to do is to start the user program it just placed in sdram, and here is the problem. It wont start the program. Btw. the user app is compiled with the same nios system as the bootloader, but is set to use only sdram for .text .ro .rw and so on What I do at the end of the bootloader is: use a void pointer and load this with the address I want to call Looks something like this (haven’t got the code in front of me right now) but its only these 2 lines userapp = 0x1000000 ; // or 0x1000034 ; _start or _main userapp(); I can see (in the objdump.file) that this creates a ADDI, a "I cant remember instruction" and at last a CALLR instruction. So this c code seems to work ok, but nothing happens. For starters my user app is simple: main calls a function that runs some LED&#39;s As described, if I jump to sdram base (_entry)(address found in user app objdump file) nothing happens. If I jump to (_start) nothing happens. If I jump to (_main) the program runs, and if I jump to (myLEDfunc) it runs. The problem is that I can see that the .heap, .stack and .exceptions +++ still uses the internal fpga memory (led flash slower when running from SDRAM). If I init irq&#39;s or init other features in my user app the jump to _main from bootloader doesn’t work. my conclusion: I’m missing something but what? >What do you mean "it loads a user app"? Are you using an instruction cache and >do you flush before jumping? NO, how do I do that ? What code did you implement at the entry point? none (using default compiler script) > What happens when you download the code (e.g. using nios2-download) ... does it work? I&#39;m not using any tools provited with the nios software >Use nios2-console and set a breakpoint just before jumping to your code. Then >step Bootloader jumps but user app crash depending on address I jump to thx for all your help and time Scott I think I need it.

Hi Rasdan, Sounds like a problem with a stray interrupt and/or the exception trampoline. If your exception address is in SDRAM, you need to: (1) disable interrupts, (2) load the image into SDRAM, (3) flush icache and the pipeline, (4) finally jump to _start. Actually you should flush the icache/pipeline no matter where your exception address is -- otherwise you run the risk of executing stale code in the icache. And even though you don&#39;t have a data cache, it&#39;s a good idea to go through the motions anyway (which will be the equivalent of a few nops) ... it will save you some headaches in the future if you decide to add dcache. But a few more questions: 1. Where is your exception address located? SDRAM? 2. How do you generate the binary file? And a few comments: > If I jump to (_start) nothing happens. - _start is the correct entry point. In your case, since .text is not in the boot device, and you have no data cache, all _start does is: (1) set the stack pointer to the top of memory, (2) sets the gp, (3) clears .bss, and (4) calls alt_main. Check your system library properties to make sure you have your stack, heap, etc. set properly. - _start does NOT call alt_load when .text is NOT in the boot device. It&#39;s your loader&#39;s responsibility to load the various sections to their proper VMA. Regards, --Scott

HELP assigning function to specific address

12 Replies

Altera_Forum
Honored Contributor
20 years ago
Hi Rasdan,

> Yes I guess this would be fatal, but only if the bootloader .exception segment
> is placed is internal ram.

Correct. If the exception address is in SDRAM, the bootloader _should_ always
copy its .exception section to the exception address -- so no problem.

> After this the bootloader (my code) probably overwrites the exception segment with
> the user app and calls it. My user application doesn’t need to copy anything because
> all segments (except reset) are defined in sdram so they are already there.
> If I, at this point, reset the cpu the bootloader should work just fine.
>
> Is this correct?

Correct.

> This only works IF the bootloader is freestanding and it doesn’t call :
>
> alt_irq_init (ALT_IRQ_BASE);
>
> Any use of this function in the bootloader will somehow crash the user application
> when i call (_start).
> I don't understand why?
> Do u have any clue to this?

This all gets back to alt_main -- when your app is "hosted" the HAL alt_main is
called ... which in turn calls alt_sys_init. And alt_sys_init is the most likely culprit.
alt_irq_init just clears the ienable (disables all external hardware interrupts), then
sets status.PIE (enables CPU response to external interrupts) -- not a problem ...
... at least not yet:

When alt_sys_init is called, the drivers for your hardware are initialized and
interrupts get enabled. My guess is: (1) you have at least 1 timer, (2) it's selected
as the system clock in your syslib properties, (3) the interrupt gets enabled, and
finally (4) the interrupt is asserted and causes problems while you are downloading
(and overwriting the exception trampoline). You can test this by selecting "none"
for your system clock timer -- see if things get better ;-)

Let us know how you make out :-)

Regards,
--Scott
Altera_Forum
Honored Contributor
20 years ago
Hi Scott,

>Let us know how you make out :-)

Status today: Everything seems to work.
I tested the interrupt system using a timer in my user application
and it works perfect.
At this time I have no further problems.

I can see a lot of people have been looking at this topic.
So for anyone reading this topic and reaching all the way down to this post.
I would like to sum up everything I did to get this far.
I will not comment on why the settings are the way they are.
This info can be found in the text above (replys).
So here goes:

TARGET:

1. Make an independent bootloader that loads a user application from a nios hardware interface into SDRAM.
(this interface could be anything rs232, parallel port, usb, TCP/IP or custom something).
My project uses a custom interface between a PowerPC and the nios.

2. Bootloader has to call and execute the user application at the end of user application transfer.

3. A nios reset should restart the bootloader so the user application
can be updated or reloaded.

NIOS HARDWARE minimum:

Nios cpu (no comment)
Internal on chip memory (program memory for bootloader)
User application memory (SDRAM in my case)
Interface hardware (my PowerPC - NIOS interface, anything could be used).

SOPC SETTINGS:

Reset address: on chip ram
Exception address: user application memory (sdram)
Break location: whatever

SOFTWARE SETTINGS (Nios IDE)

1. Bootloader:
Program mem (.text): on chip ram
Read only mem (.rodata) : on chip ram
Read/write mem (.rwdata) : on chip ram
Heap mem: on chip ram
Stack mem: on chip ram
System clock timer: select none

2. User application
Program mem (.text): SDRAM
Read only mem (.rodata) : SDRAM
Read/write mem (.rwdata) : SDRAM
Heap mem: SDRAM
Stack mem: SDRAM

SOFTWARE BOOTLOADER

This should be a freestanding application.
Use hallo freestanding as template.

Delete any init functions calls in this code
(These will probably cause something bad to happen).

//alt_sys_init();
//alt_sys_init();
//alt_io_redirect();

The first thing the bootloader should do is to
copy the user program into the user application memory.
Can’t help with this. This depends on the interface you are using)
When this is done all that is left is to call the user application, flush icache and dcache.

alt_icache_flush_all();
alt_dcache_flush_all();
AppStartP = (void*)0x10001c8; // _start address (found in objdump file)
AppStartP(); // call application

SOFTWARE USER APP:

Do whatever you need to do.

GENERATION OF USER APPLICATION UPLOAD FILE

Click Start->All programs->Altera->Nios II development kit -> nios II SDK shell
In the console use elf2hex:
elf2hex --input=userapp.elf --start=0x1000000 --end=0x1ffffff –width= 8

This creates a hex file named userapp.hex that contains the user program.
This can be changed to binary or whatever are needed using normal hex2bin tools.
It’s not needed to set end addr to the end of the sdram(my case) only to the end of user application (look in objdump file)

---------------------------------------------

This seems real simple when you know how.

-comments to Scott

>My guess is: (1) you have at least 1 timer

Correct! What a great guess

> It’s selected as the system clock in your syslib properties

Correct again!

Now Scott how do you know all this (all of it)? Your understanding of the nios system seems amazing,
you deserve the NIOS GOD status of your profile.
Your help has been amazing and I’m very grateful to you, but also to the nios
community for making this possible.
Thank you all

Feel free to comment on anything.
I will be reading any comments.

Regards,
--Rasdan

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HELP assigning function to specific address

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