Mixing Assembly code with C code serious problem

The Real Time Clock library defines these variables to be placed in the .bss section.  This section is also used by C/C++ compiler for global and static variables.

What C variables are you concerned about using the .bss section?  Or is it the C stack and system memory (for dynamic memory allocation) is spilling over into these variables?

You do have the option of placing these variables into their own named section and then allocating that section to an area of RAM which would not be impacted by the stack.

It seem to me that your problem is caused by the linking process.

Which tool chain (IAR or CCE) are you using? Which version?

IAR and CCE are not the same. Different versions of IAR are not the same. Different versions of CCE are not the same. What is the RTC Library you use intended? A mismatch can cause the linker to do silly things.

BrandonAzbell said:

What C variables are you concerned about using the .bss section?  Or is it the C stack and system memory (for dynamic memory allocation) is spilling over into these variables?

I had declared a char global variable and it always had the value of TI_year.  The memory map tool had &my_variable always pointing to TI_year location, which is bad.

BrandonAzbell said:

You do have the option of placing these variables into their own named section and then allocating that section to an area of RAM which would not be impacted by the stack.

This would be great however I looked through the several pdfs regarding coding for MSP430 (like the C optimization guide and the assembly guide) and found no concrete information. Is there a place that explains this?

I am using Version: CCE v3.1   Build: 3.2.3.6.4 

I use the RTC library to implement software real time clock. Been working great so far until this issue showed up.

Raf said:

I had declared a char global variable and it always had the value of TI_year.  The memory map tool had &my_variable always pointing to TI_year location, which is bad.

That is interesting.  The linker should allocate a space for each variable unless you explicitly do something to have it create a union or similar.

Raf said:

This would be great however I looked through the several pdfs regarding coding for MSP430 (like the C optimization guide and the assembly guide) and found no concrete information. Is there a place that explains this?

The MSP430 Optimizing C/C++ Compiler v3.1 User's Guide (SLAU132) in Section 5.8 talks about pragma directives that you can use to create data sections in C code.  However, since the RTC library is in assembly, the MSP430 Assembly Language Tools v3.1 User's Guide (SLAU131) in Section 4.2 talks about section directives.

For assembly files, you can specifiy a named section and redefine the RTC variables as .data.

     .sect "my_section"
TI_year       .word 0x0000
TI_second .byte 0x00
etc.

If you have a named section, you will then need to modify the linker command file to include this section and allocate it to a memory in the SECTIONS directive statement.

SECTIONS
{
   ...
   my_section : {} > RAM
   ...
}

Thank you for the help so far. I tried following the instructions but I'm still having a problem

This is what I have so far:

.sect "rtc" ; rtc section

TI_year .word 0x0000

TI_second .byte 0x00

TI_minute .byte 0x00

TI_hour .byte 0x00

TI_day .byte 0x00

TI_month .byte 0x00

TI_PM .byte 0x00

TI_FebDays .byte 0x00

TI_dayOfWeek .byte 0x00

TI_dayLightZone .byte 0x00

TI_dayLightSavings .byte 0x00

The lnk_msp430f2274.cmd has been modified to include the following

SECTIONS

{

    .bss     : {} > RAM                /* GLOBAL & STATIC VARS              */

    .sysmem   : {} > RAM                /* DYNAMIC MEMORY ALLOCATION AREA    */

    .rtc     : {} > RAM                /* RTC VAR               */

    .stack   : {} > RAM (HIGH)         /* SOFTWARE SYSTEM STACK             */

...

The problem is the compiler gives me a warning creating output section "rtc" without SECTIONS specification.  

Because of this warning it assigns the RTC variables to:

00000008   TI_FebDays

00000007   TI_PM

00000005   TI_day

0000000b   TI_dayLightSavings

0000000a   TI_dayLightZone

00000009   TI_dayOfWeek

00000004   TI_hour

00000003   TI_minute

00000006   TI_month

00000002   TI_second

00000000   TI_year

Which isnt RAM. Any ideas?

I know this thread is kind of old, but I thought you should know that if you are using the RTC_Calendar.s43 module, you will need to modify the "setDate (y, m, d)" function. It is erroneous.

In particular, there is an instruction that modifies R10 ("add.w   r10,     r11"), but R10 is never pushed. To fix this, add a "Push R10" at the beginning and a "Pop R10" at the end.

It's the kind of bug that gives me giggles!

Err...oops..

The offending instruction is actually "            mov.b   TI_mNumbers(r7), r10". I forgot that MSP430 assembly is written "inst src, dst".