modifying the reset handler asm code

Why assumptions?

Because you can't design _anything_ without making assumptions.

What assumptions did a car manufacturer base the design on?
- that people can buy gasoline?
- that there exists tire companies?
- that a human will sit with the legs down and the arms on the steering wheel?
- that the customers will value safety and expect safety belt, air bags, impact zones, ...
- that the customer would be angry if the noise levels did give loss of hearing.
- that a normal road doesn't have holes larger than a certain size.
- what size to expect for a normal parking space.

There are always assumptions.

Some are so obvious that you don't document them. S the car is designed for humans of "normal" size. The manufacturer leaves it up to people who are 270 cm long or weights 340 kg to check if they will fit.

Some are non-obvious and needs to be documented. So you get a document that tells the maximum weight you may transport with the car. And which specific fuel it can run on.

For majority of code written, the code is written under the assumption that someone else have already set up the processor stack. And all global variables have been given their intended start values.

If you play with the startup file, then you invalidate these design decisions, and ends up with a non-working program.

Why assumptions?

Because you can't design _anything_ without making assumptions.

What assumptions did a car manufacturer base the design on?
- that people can buy gasoline?
- that there exists tire companies?
- that a human will sit with the legs down and the arms on the steering wheel?
- that the customers will value safety and expect safety belt, air bags, impact zones, ...
- that the customer would be angry if the noise levels did give loss of hearing.
- that a normal road doesn't have holes larger than a certain size.
- what size to expect for a normal parking space.

There are always assumptions.

Some are so obvious that you don't document them. S the car is designed for humans of "normal" size. The manufacturer leaves it up to people who are 270 cm long or weights 340 kg to check if they will fit.

Some are non-obvious and needs to be documented. So you get a document that tells the maximum weight you may transport with the car. And which specific fuel it can run on.

For majority of code written, the code is written under the assumption that someone else have already set up the processor stack. And all global variables have been given their intended start values.

If you play with the startup file, then you invalidate these design decisions, and ends up with a non-working program.

Agreed, that there must be some assumptions. But the altering the designs is also allowed. Like there are cars with engine behind the drivers seat.
so i just want to shift engine behind.

i have a start up file in which SystemInit function is not called from asm.

Reset_Handler   PROC
                EXPORT  Reset_Handler             [WEAK]
                IMPORT  __main
                LDR     R0, =__main
                BX      R0
                ENDP

the asm only has __main. and then, i borrowed this new file from cmsis library where it has SystemInit function called from the asm code.

main is just a name for the tool. it must allow initialisation of os before we call main. no?

main is just a name for the tool. it must allow initialisation of os before we call main. no?

It can do nothing to disallow it. However, you must appreciate what __main does. One task is to initialise memory and the data it is expected to hold. It sets up the C runtime environment prior to main being called. A lot of the RTX is written in C. It makes use of the C facilities. You seem to be suggesting, therefore, that C should be used before the C runtime is actually permitted.

If you change the foundations the code was written based on, then you need to modify the code to make it compatible.

You don't have the code? Then that should be an indication that you are running in the wrong direction. Other people aren't stuck with this issue because they aren't fighting with wind mills.

You have gotten a bad idea in your head. The idea will not be good because you invest more time on it. The idea _could_ have been better if you had owned the source code for the CRTL + the OS, allowing you to redesign the code for the changed use case.

Yes, cars can have the engine back. But they are normally designed from the start to have the engine at the back.

You don't take an Opel from the street and just move the engine to the back. You'll have lots of very interesting problems to solve. And you'll have lots of interesting paperwork to handle.

Your current idea is like taking a three-story building and splitting it up and then reconnect the pieces again so the bottom floor is now on the top, and the top floor is on the bottom. Most other people would instead just move between the top and bottom apartments without trying to rip the building to pieces.

But the altering the designs is also allowed.

Allowed, sure. But it also requires knowing very well what that design actually is --- you have to know every detail of every assumption that went into designing all aspects of the design that you're trying to alter. Otherwise you'll just fail. Badly.

so i just want to shift engine behind.
And you won't manage to fulfill that wish if you don't know exactly how that car works.

it must allow initialisation of os before we call main. no?

No.

And you won't manage to fulfill that wish if you don't know exactly how that car works.

You obviously think you're smart by posting such a statement, but your extension to the comparison of the startup code to a complete car is just rediculous. There are many changes that can be made to a car without having to know exactly how that car works. An engine can be moved without, for example, knowing the intricacies of how the ECM works. I personally know mechanics who have done such tasks without knowing how the "black boxes" work and their results have been sweet.

What IS important is understanding the intricasies of the area involved and the associated components that might be affected.

Here, it is fairly clear to me that the OP has little real understaning of the C runtime startup sequence. If he learns about this he might find out what he can meaningfully do.

Per, Tamir, John, Andrew, Marcelle, Hans-Bernhard
Thank you guys.
The discussion was really awesome. :)

Marcelle,
you got it correct.
...the OP has little real understaning of the C runtime startup sequence. If he learns about this he might find out what he can meaningfully do.
Request all of you to give reference of good technical material, in case you know any (i m googling it already in the adjacent tab but your recommendations are priority).

Per,
It is after this discussion, i came to know about the __main, scatter file, CRTL, etc.
The idea _could_ have been better if you had owned the source code for the CRTL + the OS, allowing you to redesign the code for the changed use case.
Is there any way to get source for CRTL + the OS? Would prefer the free one.

John,
question, my thought is: Yes, and not only the procedures, but also the source code.
where and How can i get the source code?