So that would mean making a const variable for every string correct? I could make a header file to store all of those. I can't do inline in say a printf statement?

Thanks.

The strings that you would inline in a printf() statement are const. How would you modify them? :)

Consider the following code:

#include "mbed.h"

DigitalOut myled(LED1);

int main()
{
    printf("Hello world\r\n");
    while(1)
    {
        myled = 1;
        wait(0.2);
        myled = 0;
        wait(0.2);
    }
}

If we look at the disassembly we see that the printf() is converted to a puts() call since we aren't actually formatting anything and just outputting a constant string. Still valid for our investigation though. If we look at line 0x122 we see it place the address of the "Hello world\r\n" string into r0. The address it places in this register is 0x00002284, which is safely in the FLASH area on my LPC1768 where I ran this sample.

00000120 <main>:
     120:	b508      	push	{r3, lr}
     122:	4808      	ldr	r0, [pc, #32]	; (144 <main+0x24>)
     124:	f001 fc54 	bl	19d0 <puts>
...
     144:	00002284 	.word	0x00002284

We can dump the memory at 0x2284 and see our string in FLASH:

2280: 9E 46 70 47 48 65 6C 6C 6F 20 77 6F 72 6C 64 0D  .FpGHello world.
2290: 00 00 00 00 63 6F 75 6C 64 20 6E 6F 74 20 70 69  ....could not pi

I hope that helps.

Thank you taking the time to break it down. It does help! I am so used to Arduino stuff. I was thinking I was using more RAM than before. I have more RAM\flash available and yet running out with mostly the same code as on the ATmega32u4. Hard to tell if the issue is out of flash or RAM. I switched from Arch to Arch Pro and now there is enough. But final design will probably be on one of the ST Nucleo boards.

Looks like I was out of flash not SRAM. Compiling on the Pro gives me 47k. Might be smaller on the ST boards since they don't need the USB Device library.

Edit: Yup 11k less on ST vs Arch. But .6kb more SRAM.