Chapter 5 Dive Into SDK

This chapter discusses some important topics that are critical to use SDK efficiently.

5.1 Memory Management

There are mainly three type of memory management methods:

  1. Statically allocated global variables
  2. Dynamically allocated and freed on stack
  3. Manually allocated and freed on heap

RAM is shared between platform and user applications. When a new project is created by ingWizard, RAM settings is configured properly. Developers are not suggested to modify these settings.

5.1.1 Global Variables

This is the recommended way to define variables that have a full lift span in the app. They are allocated in the fixed location and their content can be checked easily in debugger.

5.1.2 Using Stack

For variables that are only used within a limited scope, such as a function, we can allocated them on stack.

Cares must be taken that size of stack is limited, and it might overflow if too much memory is allocated.

  1. The app_main function & interrupts serving routines shares the same global stack with platform’s main function.

    For RTOS bundles, this stack is defined in platform binaries as 1024 bytes, and can be replaced by a user defined one with the help of platform_install_isr_stack.

    For “NoOS” bundles, this stack is defined in app binariy as usual.

  2. Callback functions registered into Bluetooth stack shares the same task stack with the stack task, whose size is defined as 1024 bytes, and about half is left to be used by app.

  3. Developers can create new tasks by calling RTOS APIs. In these cases, stack size should be carefully examined.

Use tools to check required stack maximum depth of functions.

5.1.3 Using Heap

Generally, heap is not a recommended way for memory management in embedded applications. There are several cons included but not limited to:

  • Space Overhead

    Some bytes are wasted to store extra information and extra program.

  • Time Overhead

    It costs cycles to allocate and free memory blocks.

  • Fragmentation

Based on these considerations, the heap used by malloc & free has been totally disabled by setting its size to 0. If such heap is TRULY required, it can be re-enabled by changing its size to a proper value when creating projects. Be sure to check follow alternatives before using malloc & free:

  • Use global variables

  • Use memory pool15

    This is probably the choice for most cases.

  • Use FreeRTOS’s heap and memory functions, pvPortMalloc & pvPortFree

    Note that this heap is used by platform & FreeRTOS itself, and it may not have too much free space left for apps. The standard malloc & free can be configured to be overridden and backed by pvPortMalloc & pvPortFree when setting up heap in ingWizard. Once overridden, the allocator from libc is omitted, and malloc & free are implemented by pvPortMalloc & pvPortFree respectively.

5.2 Multitasking

It is recommend to have a check on Mastering the FreeRTOS™ Real Time Kernel. Some tips:

  1. Do not do too much processing in interrupt handlers, but defer it to tasks as soon as possible

  2. Callback functions registered into Bluetooth stack are executed in the context of the stack task, so do not do too much processing in these functions either

  3. Use message passing function btstack_push_user_msg or other special functions16 to get synchronized with Bluetooth stack (see Inter-task Communication)

5.3 Interrupt Management

To create traditional ISR for interrupts, apps only need to register callback functions through a platform API platform_set_irq_callback.

Apps can use following APIs to modify interrupts configuration and states:

  • NVIC_SetPriority

    Note that the highest allowed priority is configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY + 2, i.e. that priority parameter must be larger than or equal to this value, indicating a lower or equal priority.

  • NVIC_EnableIRQ

  • NVIC_DisableIRQ

  • NVIC_ClearPendingIRQ

  • etc…

5.4 Power Management

In most case, platform manages the power saving feature of ING918xx/ING9186xx SoC automatically and tries the minimize the power consumption in all circumstances, with only one exception, deep sleep.

In deep sleep, all components, except those required for power saving control and real-time clocks, are powered down. Some peripherals may be used by apps, and platform does not know how to configure them. So, apps have to get involved in the waking up process after deep sleep. Platform will also check with app if deep sleep is allowed, and fall back to less aggressive power saving modes when deep sleep is not allowed.

To use deep sleep, two callback functions are needed, see platform_set_evt_callback. To ease development & debug, power saving can be turned on or off by calling platform_config.

Besides the above automatic power management schema, apps can also shutdown the whole system and reboot after a specified duration. In shutdown state the whole system has the least power consumption. See platform_shutdown. In shutdown state, a portion of data can be kept optionally at the cost of a little more power consumption. In case of only a little piece of data needs to be kept, for example no more than four bits, SDK provides a pair of APIs for this, platform_write_persistent_reg and platform_read_persistent_reg.

5.5 CMSIS API

SDK tries to encapsulate CMSIS APIs to ease the development. Be careful when calling these APIs in apps as it may affect the platform program.

Following operations are strictly forbidden:

  1. Changing the vector table offset register
  2. Modify configurations of internal interrupts, i.e. those not listed in Table 6.1.

5.6 Debugging & Tracing

Besides online debugging, SDK provides two methods to assist debugging.

  1. printf

    printf is the most convenient way to check program’s behaviour. ingWizard can generate necessary code to use printf.

  2. Trace

    Internal state & HCI messages can be recorded through this trace machenism. ingWizard can generate necessary code to use trace, too. There are several types of trace data, which are predefined and can’t be changed. Which types of trace data are going to be recorded is programmable. Use

    ingTracer to view the recorded trace data.

Table 5.1: Comparison of printf and Trace
Debug Option Pros Cons
printf Universal slow
Trace Binary data, fast Data types are predefined

Both printf and trace can be directed to UART ports or SEGGER RTT17. Table 5.2 is a comparison of these two transport options.

Table 5.2: Comparison of UART and SEGGER RTT
Transport Option Pros Cons
UART Universal, easy to use Slower, consume more CPU cycles
SEGGER RTT Fast J-Link is required, hard to capture power up log

5.6.1 Tips on SEGGER RTT

  • Use J-LINK RTT Viewer to view printf outputs in real-time.

  • Use J-LINK RTT Logger to record trace outputs to files.

    This logger will ask for the settings of RTT. Device name is “CORTEX-M3”. Target interface is “SWD”. RTT Control Block address is the address of a variable named _SEGGER_RTT, which can be found in .map file. RTT channel index is 0. Blow is a sample session.

    ------------------------------------------------------------
    
    Device name. Default: CORTEX-M3 >
    Target interface. > SWD
    Interface speed [kHz]. Default: 4000 kHz >
    RTT Control Block address. Default: auto-detection > 0x2000xxxx
    RTT Channel name or index. Default: channel 1 > 0
    Output file. Default: RTT_<ChannelName>_<Time>.log >
    
    ------------------------------------------------------------
    Connected to:
      J-Link ...
      S/N: ...
    
    Searching for RTT Control Block...OK. 1 up-channels found.
    RTT Channel description:
      Index: 0
      Name:  Terminal
      Size:  500 bytes.
    
    Output file: .....log
    
    Getting RTT data from target. Press any key to quit.

    Alternativaly, this tool can be called from command line. Address of_SEGGER_RTT can be specified by a range, and the tool will search for it automatically. For examples,

    JLinkRTTLogger.exe -If SWD -Device CORTEX-M3 -Speed 4000
    -RTTSearchRanges "0x20005000 0x8000"
    -RTTChannel 0
    file_name

5.6.2 Memory Dump

We are committed to delivery high quality platform binary. If an assertion had occurred in platform binary, it is suggested to create a full memory dump and save all registers, then contact for further support. There are two memory regions (Table 5.3).

Table 5.3: Memory Regions
Region Start Address Size (Bytes)
#1 0x20000000 0x10000 (for 128kB RAM chip series)
0x08000 (for 64kB RAM chip series)
#2 0x400A0000 0x10000 (for 128kB RAM chip series)
0x08000 (for 64kB RAM chip series)

Memory can be dumped through debuggers:

  • Keil μVision

    In debug session, open the Command Window, use save to save each memory region. For example:

    save sysm.hex  0x20000000,0x2000FFFF
    save share.hex 0x400A0000,0x400AFFFF
  • J-Link Commander

    Once connected, use regs to shows all current register values, and savebin to save target memory into binary file. For example:

    savebin sysm.bin  0x20000000 0x10000
    savebin share.bin 0x400A0000 0x10000
  • IAR Embedded Workbench

    In debug session, open a Memory window, and select “Memory Save …” from popup menu.

  • Rowley Crossworks for ARM & SEGGER Embedded Studio for ARM

    In debug session, open a Memory window, for each memory region:

    1. Fill in the start address and size;
    2. Use “Memory Save …” from popup menu.
  • GDB (GNU Arm Embedded Toolchain and Nim)

    In GDB debug session, use dump command to save each memory region.

Memory can be also dumped by a piece of specific code. For example, in the event handler of PLATFORM_CB_EVT_ASSERTION, dump all memory data to UART.