MSP432E401Y: Assembler directive similar to ORG

Brad McMillan

Part Number: MSP432E401Y
Other Parts Discussed in Thread: TM4C1294NCPDT

Hi,

I'm writing assembly code in CCS and I would like to be able to place my code at specific locations in memory. With previous assemblers I've used I was able to do this using the assembler directive ORG, but I haven't seen anything in the literature that gives me the same functionality in CCS.

Does anyone know if there is a similar assembler directive I can use in CCS?

Thank you for any responses.

over 2 years ago

0 Bruce McKenney over 2 years ago

Guru 99095 points

The assembler doesn't decide where code goes in memory, rather the linker does. You can put the code of interest in a separate section with .sect, then tell the linker to put that section at the location you want using the .cmd file in your project, either by splitting off a MEMORY area or using ">[address]".

There's a bit more detail over here:

https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1098592/msp432e401y-assembly-code-org-directive

If you can explain your overall goal, there may be an easier way to do it.

0 George Mock over 2 years ago

TI__Guru**** 249185 points

I presume you use the TI proprietary Arm toolchain. If you use a different toolchain, the concepts are the same, but some of the lower level details are different.

Brad McMillan said:
if there is a similar assembler directive I can use in CCS?

No. It doesn't work that way.

To understand how it works, please search the TI ARM assembly tools manual for the chapter titled Introduction to Object Modules. For an introduction to linker command files, please see the article Linker Command File Primer.

Thanks and regards,

-George

0 Brad McMillan over 2 years ago in reply to Bruce McKenney

Intellectual 620 points

Bruce:

WRT my overall goal I want to create a block of code that cannot be read or copied by using the memory protection unit (section 2.2.4 of slau723a) or read-only protection (section 7.2.6.6 of slau723a).

My understanding is that the block of protected memory cannot contain any literal data so my plan is to create some code without literal data and place it at a particular place in memory and protect it from being copied.

BTW, it's still not clear to me which approach is better - using the memory protection unit or using read-only protection - in order to create a block of code that cannot be read or copied. Any insight you can provide about this would also be very helpful.

Thank you once again for your assistance.

Brad

0 Bruce McKenney over 2 years ago in reply to Brad McMillan

Guru 99095 points

The MPU is configured at runtime, so if an attacker can e.g. start a debugger (at Reset) the MPU isn't configured and that block is readable. From your description, it sounds like that's not what you're interested in.

The read-protection applies to the flash blocks themselves, so it is in effect at all times. It can only be cleared using a factory reset (which includes a mass-erase).

I don't have any experience with the read-protection mechanism, but I did find document SPMA044A which describes an example:

https://www.ti.com/lit/an/spma044a/spma044a.pdf

The steps are more or less as you think:

1) Keep constants out of .text (Build Settings->Build->Compiler->Advanced->Specify whether constants can be embedded)

2) Re-build the runtime library with that option

3) Carve out a MEMORY section (on a flash block boundary) in the linker .cmd file and put .text there.

4) Call FlashProtectSet() followed by FlashProtectSave(). This only has to be done once (with your final code loaded).

0 Brad McMillan over 2 years ago in reply to Bruce McKenney

Intellectual 620 points

Bruce,

Re: spma044a: This looks like it is exactly what I'm trying to achieve. Thank you! It says it is for Stellaris microcontrollers. I assume these functions will work with the MSP432E401Y I'm using.

I'd like to try a test implementation to see how it works, but there's one issue that's not clear to me. On page 32 it says "Note that the Flash protection settings can be reset to their factory default configuration by performing the debug port unlock sequence using LM Flash Programmer".

I'm using CCS 11.2.0 and it's not clear to me how to perform a debug unlock sequence. Is the LM Flash Programmer a different program?

Thank you for your response.

Brad

0 Charles Tsai over 2 years ago in reply to Brad McMillan

TI__Guru**** 190696 points

Hi,

Please follow section 5.3.1 of this app note to unlock the device. https://www.ti.com/lit/pdf/slaa777

+1 Brad McMillan over 2 years ago in reply to Charles Tsai

Intellectual 620 points

I got it working. Thank you all for your assistance.

+1 Bruce McKenney over 2 years ago in reply to Brad McMillan

Guru 99095 points

To answer your other question: The MSP432E401Y is really a Tiva (TM4C1294), which is descended from the Stellaris series, which is in turn descended from the Luminary Micro LM3S series. I found that document on the TM4C1294NCPDT product page, along with some other interesting reading.

0 Brad McMillan over 2 years ago in reply to Bruce McKenney

Intellectual 620 points

A very impressive line of microcontrollers.

Arm-based microcontrollers

Arm-based microcontrollers forum

MSP432E401Y: Assembler directive similar to ORG