Debugging¶

Connecting to the XDS Debugger¶

If only one debugger is attached, the IDE uses it automatically when you click the button in CCS.

If multiple debuggers are connected, you must choose the individual debugger to use. The following steps detail how to select a debugger in CCS.

Find Serial Number¶

To find the serial number for XDS100v3 debuggers, do as follows.

1. Open a command prompt.
2. Run C:\ti\ccsv7\ccs_base\common\uscif\xds100serial.exe to get a list of serial numbers of the connected debuggers.

For XDS110 debuggers (Launchpads), run the following command: c:\ti\ccsv7\ccs_base\common\uscif\xds110\xdsdfu.exe -e

Configure serial number¶

Open the target configuration file.
Open the Advanced pane.
Choose the top-level debugger entry.
Enter the serial number.

Breakpoints in CCS¶

To toggle a breakpoint, do any of the following.

• Double-click the area to the left of the line number.
• Press Ctrl+Shift+B.
• Right-click on the line.

A breakpoint set on line 207 looks like the following.

Figure 73. Breakpoint on line 207. Debugger halted at start of main().

For an overview of the active and inactive breakpoints, click on View –> Breakpoints.

Figure 74. List of breakpoints. Right-click to edit options, or de-select to deactivate.

To set a conditional break, do as follows.

1. Right-click the breakpoint in the overview.
2. Choose Properties.

When debugging, Skip Count and Condition can help skip a number of breaks or only break if a variable is a certain value.

Breakpoints and Timing¶

Synchronous RF protocols like the Bluetooth low energy protocol are timing sensitive, and breakpoints can easily halt the execution long enough to lose network timing and break the link.

To still be able to debug, place breakpoints as close as possible to where the relevant debug information can be read or step through the relevant code segment to debug.

After you hit a breakpoint and read out the necessary debug information, it is recommended that you reset the device and re-establish the connection.

Breakpoints and Optimization¶

When compiler optimizations are enabled, toggling a breakpoint on a line of C code may not result in the expected behavior. Some examples include the following.

Code is removed or not compiled in

Toggling a breakpoint in the IDE results in a breakpoint some other unintended place and not on the selected line. Some IDEs disable breakpoints on nonexisting code.

Code block is part of a common subexpression

For example, a breakpoint might toggle inside a function called from one other function, but can also break due to a call from another unintended function.

An if clause is represented by a conditional branch in assembly

A breakpoint inside an if clause always breaks on the conditional statement, even if not executed.

TI recommends selecting an optimization level as low as possible when debugging. See Optimizations for information on modifying optimization levels.

Variables in CCS¶

You can view Global Variables by doing either of the following.

• Select View –> Expressions
• Select a variable name in code.
  • Right-click and select Add Watch Expression.

Figure 75. Variable watch window. Note that you can cast values, get address and sizeof, etc.

• Select View –> Variables to auto-variables that are present at the current location when stepping through code.

Figure 76. Local variables. This screenshot is taken during execution of the Simple Peripheral init function.

Considerations When Viewing Variables¶

Local variables are often placed in CPU registers and not on the stack. These variables also have a limited lifetime even within the scope in which they are valid, depending on the optimization performed. CCS may struggle to show a particular variable due to its limited lifetime. The solution when debugging is as follows.

• Move the variable to global scope, so it remains accessible in RAM.
• Make the variable volatile, so the compiler doesn’t place the value in a register.
• Make a shadow copy of the variable that is global and volatile.

Watchpoints in CCS¶

1. Right-click on a global variable.
2. Select Breakpoint –> Hardware Watchpoint
3. Go to the list of breakpoints (View –> Breakpoints)
4. Right-click and edit the Breakpoint Properties to configure the watchpoint.

Figure 77. Adding a watchpoint on a variable.

This example configuration ensures that if 0x42 is written to the memory location for Characteristic 1 in the Bluetooth low energy simple_peripheral example project the device halts execution.

Figure 78. Configuring a hardware watchpoint to break on 8-bit write with value 0x42.

Scanning the BIOS for Errors¶

The BIOS Scan for errors view goes through the available ROV modules and reports on errors. This functionality can be a good point to start if anything has gone wrong. This scan only shows errors related to TI-RTOS modules and only the errors it can catch.

Figure 79. Scan for errors. Here a Task Stack has been overrun.

Viewing the State of Each Task¶

The Task Detailed view is useful for seeing the state of each task and its related runtime stack usage. This example shows the state the first time the user-thread is called. Figure 80. shows the Bluetooth low energy stack task, represented by its ICall proxy, the Idle task, the simple_peripheral task and the GAPRole task.

Figure 80. Detailed view of the Tasks. Notice the address of the overrun task matches the instance id from Scan for errors.

The following list explains the column in Figure 80.

address

This column shows the memory location of the Task_Struct instance for each task.

priority

This column shows the TI-RTOS priority for the task.

mode

This column shows the current state of the task.

fxn

This column shows the name of the entry function of the task.

arg0, arg1

These columns show abitrary values that can be given to entry function of the task. In the image, the ICall_taskEntry is given 0xb001, which is the flash location of the entry function of the RF stack image and 0x20003a30 (the location of bleUserCfg_t user0Cfg, defined in main()).

stackPeak

This column shows the maximum run-time stack memory used based on watermark in RAM, where the stacks are prefilled with 0xBE and there is a sentinel word at the end of the run-time stack.

stackSize

This column shows the size of the runtime stack, configured when instantiating a task.

stackBase

This column shows the logical top of the runtime stack of the task (usage starts at stackBase + stackSize and grows down to this address).

Viewing the System Stack¶

The Hwi –> Module view allows profiling of the system stack used during boot or for main(), Hwi execution, and SWI execution. See System Stack for more information on the system stack.

Figure 81. Viewing the System Stack in Hwi

The hwiStackPeak, hwiStackSize, and hwiStackBase can be used to check for system stack overflow.

Functions¶

void ICall_heapGetMetrics(u16 *pBlkMax, u16 *pBlkCnt, u16 *pBlkFree, u16 *pMemAlo, u16 *pMemMax, u16 *pMemUb)

Returns the previously described variables in the pointers passed in as parameters

int heapmgrSanityCheck(void)

Returns 0 if the heap is ok; otherwise, returns a nonzero (that is, an array access has overwritten a header in the heap)

Determining the Auto Heap Size¶

The following procedure can be used to view the size of the ICall heap when the auto heap size feature is enabled (HEAPMGR_SIZE=0).

At runtime, view the value of the global memory symbol HEAPMGR_SIZE after ICall_init() has been executed in main(). The value of HEAPMGR_SIZE is the total size of the ICall heap. See HEAPMGR_INIT() in heapmgr.h for the source code implementation.

• In CCS Debug Session: View -> Expressions, add HEAPMGR_SIZE

To calculate the size of the ICall heap by inspecting the application map file in CCS:

The size of the heap is determined by the heapStart and heapEnd global symbol addresses which are emitted by the linker. For example, the simple_peripheral_cc2650lp_app.map file:

20003f48  heapEnd
20001cc1  heapStart

The size of the ICall heap in this example is defined as: 0x20003f48 - 0x20001cc1 = 0x2287 or 8839 bytes for the heap.

Project-Wide Optimizations¶

For debugging, ideally, the project-wide settings for optimization should be as low as possible. There may not be enough available space on the target to do this, but lowering just a couple of levels can be helpful.

In CCS

Project Properties –> CCS Build –> ARM Compiler –> Optimization

Figure 82. Project-level optimization setting in CCS

Single-File Optimizations¶

In CCS

1. Right-click on the file in the Workspace pane.
2. Choose Properties.
3. Change the optimization level of the file using the same menu in the CCS project-wide optimization menu.

Single-Function Optimizations¶

Using compiler directives, you can control the optimization level of a single function.

In CCS

#pragma FUNCTION_OPTIONS(myFunction, "--opt_level=0")
static void myFunction(int number)
{
  // ...
  return yourFunction(other_number);
}

Loading TI-RTOS in ROM Symbols¶

Some of the TI-RTOS kernel modules are included in ROM, and executed from ROM in order to save Flash space for the application. This can lead to some confusion, when only addresses are shown in the disassembly view and the call-stack view.

All TI-RTOS kernel code in ROM starts with address 0x1001xxxx. In order to make sense of the ROM’ed code, you need to include the symbol files in your debug session.

In CCS

Figure 83. Adding symbol information for the BIOS kernel in ROM, via Add Symbols.

• While in debug mode, click the drop-down button next to the Load Program icon
• Select Add Symbols..
• Select Browse.. and find
• <SDK\_INSTALL\_DIR>\kernel\tirtos\packages\ti\sysbios\rom\cortexm\cc26xx\r2\golden\CC26xx\rtos_rom.xem3

Exception Cause¶

With the default setup using TI-RTOS, the exception cause can be found in the System Control Space register group (CPU_SCS) in the register CFSR (Configurable Fault Status Register). The ARM Cortex-M3 User Guide describes this register. Most exception causes fall into the following three categories.

• Stack overflow or corruption leads to arbitrary code execution.
  • Almost any exception is possible.
• A NULL pointer has been dereferenced and written to.
  • Typically (IM)PRECISERR exceptions
• A peripheral module (like UART, Timer, and so forth) is accessed without being powered.
  • Typically (IM)PRECISERR exceptions

The CFSR register is available in View –> Registers in CCS.

When an access violation occurs, the exception type is IMPRECISERR because writes to flash and peripheral memory regions are mostly buffered writes.

If the CFSR:BFARVALID flag is set when the exception occurs (typical for PRECISERR), the BFAR register in CPU_SCS can be read out to find which memory address caused the exception.

If the exception is IMPRECISERR, PRECISERR can be forced by manually disabling buffered writes. Set [CPU_SCS:ACTRL:DISDEFWBUF] to 1, by either manually setting the bit in the register view in CCS or by including <hw_cpu_scs.h> from Driverlib and calling the following.

#include <ti/devices/cc26x0r2/inc/hw_cpu_scs.h>
//..
int main()
{
  // Disable write-buffering. Note that this negatively affect performance.
  HWREG(CPU_SCS_BASE + CPU_SCS_O_ACTLR) = CPU_SCS_ACTLR_DISDEFWBUF;

  // ..
}

Using TI-RTOS and ROV to Parse Exceptions¶

To enable exception decoding in the RTOS Object View (ROV) without using too much memory, use the Minimal exception handler in TI-RTOS. The default choice in the TI 15.4-Stack projects is to use no exception handler.

To set this up, change the section of the TI-RTOS configuration file that relates to M3Hwi so that it looks like the code below:

//m3Hwi.enableException = true;
m3Hwi.enableException = false;
//m3Hwi.excHandlerFunc = null;
m3Hwi.excHookFunc = "&execHandlerHook";

Then, make a function somewhere with the signature void (*Hwi_ExceptionHookFuncPtr)(Hwi_ExcContext*); such as the one below:

#include <ti/sysbios/family/arm/m3/Hwi.h>
// ...
volatile uintptr_t *excPC = 0;
volatile uintptr_t *excCaller = 0;
// ...
void execHandlerHook(Hwi_ExcContext *ctx)
{
    excPC = ctx->pc;     // Program counter where exception occurred
    excCaller = ctx->lr; // Link Register when exception occurred

    while(2);
}

Setting m3Hwi.enableException to false enables the minimal handler, which fills out the global Hwi_ExcContext structure that the ROV looks at to show the decoded exception. By setting up an excHookFunc, the minimal exception handler will call this function and pass along a pointer to the exception context for the user to work with. This structure is defined in <ti/sysbios/family/arm/m3/Hwi.h>.

When an exception occurs, the device should end up in that infinite loop. Inspect the ROV -> Hwi -> Exception information.

Figure 84. Decoded exception, intentional write to address 0x0013 which is illegal. Note that writebuffering has been disabled to get a precise error location, and that m3Hwi.enableException has been set to false to get the decoding.

In this case, a bus fault was forced in the function writeToAddress by dereferencing address 0x0013 and trying to write to it:

void writeToAddress(uintptr_t *addr, int val)
{
   *(int *)addr = val;
}

// ..

void taskFxn(...)
{
   // ..
   writeToAddress( (void*)19, 4 ); // Randomly chosen values
}

The write instruction was placed on line 79 of application.c, as indicated. To get a precise location, the write buffer was disabled as described earlier.

It can be instructive to look at the disassembly view for the locations specified by PC (program counter) and LR (link register). PC is the presumed exception location, and LR is normally the location the failing function should have returned to. As an example, the PC at this exception:

Figure 85. Here the pc from the decoded exception was looked up in the disassembly view.

Some forensics is required here. We have from the Hwi decoding in ROV (and from the exception context in the exception hook) that the program counter was 0x708e when the exception occurred.

At that location there is a store instruction str r0, [r1] meaning, store the value in R0 to the memory address in R1. The business with SP in the figure above is related to optimization being turned off, so all local variables are stored on the stack, even though in this case R0 and R1 could have been used directly from the caller.

Now we know that the exception occured because soneone called writeToAddress with an invalid address.

Thanks to the exception decoder we can easily find the call site by looking at the call stack, but if the call stack isn’t helpful, we can look at lr, which is seen in the exception decoder to be 0x198f

Figure 86. Call site as specified in lr. Note that lr is the instruction after the call to writeToAddress because execution would have resumed here.

We can see here that R0 and R1 are initialized with constants. This means that some programmer has intentionally called the write function with an address that causes a busfault.

Most often the reason for a bus-fault is that a pointer is not initialized and a function like writeToAddress gets the pointer, assumes it’s valid and dereferences the pointer and writes to the invalid address.

Task and System Stack Overflow¶

If an overflow on the runtime stack of the task or the system stack occurs (as found using the ROV plug-in), perform the following steps.

1. Note the current size of the runtime stack of each task.
2. Increase by a few 100 bytes as described in Initializing a Task and System Stack
3. Reduce the runtime stack sizes so that they are larger than their respective stackPeaks to save some memory.

Dynamic Allocation Errors¶

Profiling the ICall Heap Manager (heapmgr.h) describes how to use the ICall Heap profiling functionality. To check if dynamic allocation errors occurred, do as follows:

1. Check whether heapmgrMemAlo or heapmgrMemAlo are close to HEAPMGR_SIZE
2. Check memFail to see if allocation failures have occurred.
3. Call the sanity check function.

If the heap is sane but there are allocation errors, increase HEAPMGR_SIZE and see if the problem persists.

You can set a breakpoint in heapmgr.h in HEAPMGR_MALLOC() on the line hdr = NULL; to find an allocation that is failing.

To disable a symbol, put an x in front of the name. To disable power management, change POWER_SAVING to xPOWER_SAVING.

Options¶

Table 20. lists the preprocessor symbols used by the application in the simple_peripheral project. Symbols that must remain unmodified are marked with an N in the Modify column while modifiable; configurable symbols are marked with a Y.

Table 21. lists the only stack preprocessor options that may be modified: