My 1802 target for LCC just defines and initializes globals in the static assembly so that, for example, if you restart it, the original initializers are not refreshed. Is that standard C?

I'm working now on a target that splits the code off for ROM and I need a way to initialize RAM globals.

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bill rowe <[email protected]> writes:

My 1802 target for LCC just defines and initializes globals in the
static assembly so that, for example, if you restart it, the original initializers are not refreshed. Is that standard C?

I'm working now on a target that splits the code off for ROM and I
need a way to initialize RAM globals.

I'm not certain what behavior you're describing.

This program:

#include <stdio.h>
int global = 10;
int main(void) {
printf("%d ", global);
global = 20;
printf("%d\n", global);
}

must print "10 20" every time it's executed. If it prints "10 20"
the first time and "20 20" the second time, the implementation is
not conforming. (Replace printf by some other mechanism if the
target doesn't support stdio.)

--
Keith Thompson (The_Other_Keith) [email protected]
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */

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On Monday, November 2, 2020 at 4:29:09 PM UTC-5, Keith Thompson wrote:

bill rowe <[email protected]> writes:

My 1802 target for LCC just defines and initializes globals in the
static assembly so that, for example, if you restart it, the original initializers are not refreshed. Is that standard C?

I'm working now on a target that splits the code off for ROM and I
need a way to initialize RAM globals.

I'm not certain what behavior you're describing.

This program:

#include <stdio.h>
int global = 10;
int main(void) {
printf("%d ", global);
global = 20;
printf("%d\n", global);
}

must print "10 20" every time it's executed. If it prints "10 20"
the first time and "20 20" the second time, the implementation is
not conforming. (Replace printf by some other mechanism if the
target doesn't support stdio.)

--
Keith Thompson (The_Other_Keith) [email protected]
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */

well, for some definition of "every time it's executed" ;-) In a small computer where there's no operating system, the C program gets loaded by itself and the loaded binary has the initialized variables in it. If, after it has run and printf'd, you
reset the computer to run it again without reloading the binary, it will print 20 twice.

That's fine if you know about it, the real kicker is if the code has to go in ROM and the data in RAM so it's only *ever* loaded once. I need a mechanism to get my LCC generated program to copy init values to the RAM "*every* time it's executed" or
restarted. I can work around it by init'ing the globals at the top of main but i'm hoping someone has a more integrated approach.

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bill rowe <[email protected]> writes:

On Monday, November 2, 2020 at 4:29:09 PM UTC-5, Keith Thompson wrote:

bill rowe <[email protected]> writes:

My 1802 target for LCC just defines and initializes globals in the
static assembly so that, for example, if you restart it, the original
initializers are not refreshed. Is that standard C?

I'm working now on a target that splits the code off for ROM and I
need a way to initialize RAM globals.

I'm not certain what behavior you're describing.

This program:

#include <stdio.h>
int global = 10;
int main(void) {
printf("%d ", global);
global = 20;
printf("%d\n", global);
}

must print "10 20" every time it's executed. If it prints "10 20"
the first time and "20 20" the second time, the implementation is
not conforming. (Replace printf by some other mechanism if the
target doesn't support stdio.)

well, for some definition of "every time it's executed" ;-) In a small computer where there's no operating system, the C program gets loaded
by itself and the loaded binary has the initialized variables in it.
If, after it has run and printf'd, you reset the computer to run it
again without reloading the binary, it will print 20 twice.

That's fine if you know about it, the real kicker is if the code has
to go in ROM and the data in RAM so it's only *ever* loaded once. I
need a mechanism to get my LCC generated program to copy init values
to the RAM "*every* time it's executed" or restarted. I can work
around it by init'ing the globals at the top of main but i'm hoping
someone has a more integrated approach.

Hmm. I've never worked with that kind of bare-metal implementation.

Here's what the C standard says about program startup for freestanding implementations:

In a freestanding environment (in which C program execution
may take place without any benefit of an operating system),
the name and type of the function called at program startup are
implementation-defined. Any library facilities available to a
freestanding program, other than the minimal set required by
clause 4, are implementation-defined.

The effect of program termination in a freestanding environment
is implementation- defined.

(The "function called at program startup" is "main" in a hosted implementation.)

Objects with static storage duration ("globals") are initialized
during program startup. If "program startup" effectively happens
only once, then yes, that's a problem. It would be nice if there
were some implementation-specific method to reload everything as
if the program were starting up again. If not, you'll probably
just have to reinitialize stuff manually.

Does "restarting" the application execute an entry point function, corresponding to "main" in a hosted environment? If so, I'd normally
expect globals to be initialized before that function begins.
If it doesn't, I'd argue that the implementation is non-conforming. Unfortunately, knowing that doesn't do you much good.

--
Keith Thompson (The_Other_Keith) [email protected]
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */

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In article <[email protected]>, [email protected] says...

My 1802 target for LCC just defines and initializes globals in the
static assembly so that, for example, if you restart it, the
original initializers are not refreshed. Is that standard C?

I'm working now on a target that splits the code off for ROM and I
need a way to initialize RAM globals.

For a stand-alone system it is not so much that the compiler does this,
as it is that you need to coordinate the compiler generated modules
with the linker and (custom?) libraries to get things where you want
them in ROM and RAM. You may need a 'program-launcher' routine (for
C run-time start-off / _crtso_()) like the following illustration -

---------------------------8>< snip here ---------------------------
#include "ROM_DEFS.h" // where ram_init_image blob is in ROM
#include "RAM_DEFS.h" // RAM init and zeroed bases & lengths

extern void main(void); // for stand-alone

void _crtso_(void) {
sys_start:
// power-up/reset comes here w/o stack call, frame, etc.

// may need to use assembly code to init stack pointer here

// here, all args are compile/link time constants -
memcopy(&init_ram_base, &ram_init_image, RAM_INIT_LENGTH);
memset(&zero_ram_base, 0, RAM_ZERO_LENGTH);

main(void); // perhaps sets-up interrupts
exit(void); // does not return

// never reached, so no return
}

void exit(void) {
while(1) ; // interrupts still running forever?

// never reached, so does not return
}
---------------------------8>< snip here ---------------------------

You need to put all your initiaized (RAM) globals into one (separate)
module, and compile/link it into a binary blob image to be placed
into ROM. Putting all your default-zeroed globals into their own
module helps make them into a contigious RAM block for memset().
You have to cover your own globals, and any in libraries too.
Code and read-only globals might be linked into ROM.

LCC needs you to do this manualy. Other compilers like SDCC try to
help you to specify them in the program source.

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