Setting AM335x CPU mode (privileged/user)

Paul Van den Bergh

Hi,

I'm working on a bare metal C++ application that needs to set various peripheral registers. I'm using CCS Version: 6.1.0.00104 with BeagleBone Black and BlackHawk USB100v2.

After launching the debugger (BeagleBone_Black.ccxml) and running my programm, writes to memory locations in the Control Module (0x44E10000 - 0x44E11FFF) doesn't change the actual memory content. I think I'm running in User mode and need privileged mode. So, my question(s) are:

- How can I known the effective cpu mode ?

- How can I switch between cpu-modes (from user to privileged) ?

I have googled on this subject to no avail...

I have examined StarterWare source to no avail (CPUSwitchToPrivilegedMode() doesn't work, results in a deadloop @ 0x00020008)

Any help/advise is welcome.

Thanks in advance,

Paul

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi Paul,

This information can be found in the ARM core documentation, available on http://infocenter.arm.com/help/index.jsp . Look for the Cortex-A8, revision r3p2 Technical Reference Manual. The system control coprocessor, register C1 should be what you are looking for.

0 Paul Van den Bergh over 10 years ago in reply to Biser Gatchev-XID

Intellectual 290 points

Hi Biser,

Thanks for your answer.

I found the document and C1 register documentation. AFAICS this register is accessible in secure privileged modes only. Since the program is in user mode when entering main(), I'm not sure if this is the way to go.

However, I tested the Starterware Demo app, it starts in privileged mode. Have to figure out how comes my app doesn't. Hints are welcome!

regards,
Paul

0 Biser Gatchev-XID over 10 years ago in reply to Paul Van den Bergh

TI__Guru**** 393215 points

I will suggest you ask on the Starterware forum: e2e.ti.com/.../790 since this forum only supports Linux and this isn't an issue we see normally.

0 Paul Van den Bergh over 10 years ago in reply to Biser Gatchev-XID

Intellectual 290 points

Ok, thanks. Will post in the suggested forum.

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Setting AM335x CPU mode (privileged/user)