I have a Silicon Labs Giant Gecko Starter Kit connected to the PC by USB. What I would like to do is to Lock the debug access to the device and then unlock it again using the JLinkARM.dll and SWD communication.

First I verify that the device is not locked by reading the IDR register.
In JLink commander I do this by writing:
// First Write 0x000000F0 to SELECT to select
// the last register bank of AP #0.
SWDWriteDP 2 0x000000F0
//Dummy-read the fourth register in this
// bank (A[3:2] == 0b11), this is the IDR register.
SWDReadAP 3
// Read the RDBUFF register to get the
// actual contents of IDR
SWDReadDP 3

This works perfectly fine.

When I do the same thing by using the JLinkARM.dll I do this:

JLINKARM_EMU_SelectByUSBSN(SerialNumber);
JLINKARM_Open();
JLINKARM_TIF_Select(JLINKARM_TIF_SWD);
JLINKARM_SetSpeed(4000);
JLINKARM_CORESIGHT_WriteAPDPReg(2, 0, 0x000000F0);
JLINKARM_CORESIGHT_ReadAPDPReg(3, 1, Data);
JLINKARM_CORESIGHT_ReadAPDPReg(3, 0, Data);

When the device is unlocked this works fine and I get the expected result in the variable Data.

However when I then lock the debug access to the device, I try to redo the sequence above to verify that the device is locked.

When using the JLink Commander I get the expected result. But when I use the JLinkARM.dll I get an error when running the CORESIGHT_Write command. The errorcode is -1.

I know that the device really is locked BTW.

Why is this not working? Does anyone have any idea to help me debug this?
I have attached a screenshot of what I get when I use the JLink Commander to read the IDR register on the locked device.

Thanks in advance for your help!

Regards,
Kristian