simplelink: TI SimpleLink MCU Platform

The objective of this wiki is to provide extensive self-help resources including technical collateral and information for developing and running Contiki-NG on TI SimpleLink™ devices.

The TI SimpleLink MCU Platform is TI’s microcontroller platform for wired and wireless devices, which provides a single software development environment for all SimpleLink devices. Currently, only the CC13xx and CC26xx device family is supported.

Please note:

Release v4.3 only supports Revision C for all CC13x2 and CC26x2 devices. For Revision E support you need to use branch develop as of 31th May 2019. Please refer to the following E2E forum post to find out which revision your device is.
TSCH support is present on this platform since Contiki-NG release 4.6 (November 2020). It has been successfully tested on most boards supported by this platform, including CC2650, CC2652R1, CC1310, and CC1312R1 LaunchPads. However, note that not all board and configurations have been tested and some problems have been reported, for example, TSCH on CC1352P1 currently has problems in the 2.4 GHz mode, and in the sub-GHz mode it fails to interoperate with other devices, e.g. CC1312R1.

For the CC13xx and CC26xx device family, the following development boards are supported:

LaunchPads, relevant files and drivers are under launchpad/
SensorTags, relevant files and drivers are under sensortag/
- CC1350 SensorTag
- CC2650 SensorTag
SmartRF06 Evaluation Board, relevant files and drivers are under srf06/
- CC13x0 EVM
- CC26x0 EVM

The platform code can be found under $(CONTIKI)/arch/platform/simplelink/cc13xx-cc26xx, and the CPU code can be found under $(CONTIKI)/arch/cpu/simplelink-cc13xx-cc26xx. This port is only meant to work with 7x7 mm chips. Contributions to add support for other chip types is always welcome.

This guide assumes that you have basic understanding of how to use the command line and perform basic admin tasks on UNIX family OSs.

Port Features

The platform has the following key features:

TI SimpleLink MCU Platform integration with Contiki-NG.
- NoRTOS integration
- TI drivers
- SimpleLink middleware plugins
Support for both CC13x0/CC26x0 and CC13x2/CC26x2 devices.
Deep Sleep support with RAM retention for ultra-low energy consumption.
Support for CC13xx prop mode: IEEE 802.15.4g-compliant Sub-1 GHz operation.
Support for CC26xx ieee mode: IEEE 802.15.4-compliant 2.4 GHz operation.
Concurent BLE beacons.

In terms of hardware support, the following drivers have been implemented:

LaunchPad
- LEDs
- Buttons
- External SPI flash
SensorTag
- LEDs
- Buttons
- Board sensors
  - Buzzer
  - Reed relay
  - MPU9250 - Motion processing unit
  - BMP280 - Digital pressure sensor
  - TMP007 - IR thermophile sensor
  - HDC1000 - Humidity and temperature sensor
  - OPT3001 - Light sensor
- External SPI flash
SmartRF06 EB peripherals
- LEDs
- Buttons
- UART connectivity over the XDS100v3 backchannel

Requirements

To use the port you need:

TI’s CC13xx/CC26xx Core SDK. The correct version will be installed automatically as a submodule when you clone Contiki-NG.
Contiki can automatically upload firmware to the nodes over serial with the included cc2538-bsl script. Note that uploading over serial does not work for the Sensortag, you can use TI’s Uniflash in this case.
A toolchain to build firmware:
- If you use the docker image or the vagrant image, this will be pre-installed for you. Otherwise, depending on your system, please follow the respective installation instructions (native Linux / native mac OS).
- TI’s Code Composer Studio can be used to build and debug Contiki-NG applications for the SimpleLink platform, which is especially useful when developing on Windows. Refer to Set up Contiki-NG in Code Composer Studio for more details.
The SRecord package for manipulating EPROM load files.
- For Windows, see the srecord homepage.
- For Linux, install via apt-get,
```
  $ sudo apt-get install srecord
```
- For OS X, install via Homebrew,
```
  $ brew install srecord
```

For additional help on how to set your system up, you may also find the guides below useful:

Examples

To build an example with the SimpleLink platform, you need to set TARGET=simplelink. In addition, you need to set the BOARD variable to the board name corresponding to the device you are using. For example, using the CC1310 LaunchPad would yield the following command make TARGET=simplelink BOARD=launchpad/cc1310.

You can view all available boards by running make TARGET=simplelink boards. The BOARD variable defaults to srf06/cc26x0 (which is the SmartRF06 EB + CC26X0EM) if not specified. Currently, the following boards are supported:

Board	`BOARD`
CC1310 LaunchPad	`launchpad/cc1310`
CC1312R1 LaunchPad	`launchpad/cc1312r1`
CC1350 LaunchPad	`launchpad/cc1350`
CC1350 LaunchPad for 433 MHz	`launchpad/cc1350-4`
CC1352R1 LaunchPad	`launchpad/cc1352r1`
CC1352P LaunchPad	`launchpad/cc1352p`
CC2650 LaunchPad	`launchpad/cc2650`
CC26x2R1 LaunchPad	`launchpad/cc26x2r1`
CC1350 SensorTag	`sensortag/cc1350`
CC2650 SensorTag	`sensortag/cc2650`
Srf06EB+CC13x0EM	`srf06/cc13x0`
Srf06EB+CC26x0EM	`srf06/cc26x0`

If you want to switch between building for one platform to the other, make certain to run make clean before building for the new one, or you will get linker errors.

To generate an assembly listing of the compiled firmware, supposing BUILD_DIR_BOARD = <build-dir-board> and CONTIKI_PROJECT = <contiki-project> in the respective Makefiles, run make TARGET=simplelink BOARD=<board> <build-dir-board>/<contiki-project>.lst. For example, considering the CC2650 SensorTag and the hello-world project, you can run make TARGET=simplelink BOARD=sensortag/cc2650 build/simplelink/sensortag/cc2650/hello-world.lst. This may be useful for debugging or optimizing your application code. To intersperse the C source code within the assembly listing, you must instruct the compiler to include debugging information by adding DEBUG = 1 to the project Makefile and rebuild by running make clean && make.

There are currently no platform-specific examples for the SimpleLink platform. However, any of the platform-agnostic examples can be used. More details about examples can be found in their respective READMEs.

How to Program your Device

In general terms, there are two possible ways to program your device:

Over JTAG. This is always possible.
Using the serial ROM bootloader. Some conditions need to be met before this is possible.

Over JTAG

The build process will output firmware in multiple formats: a *.bin file, a *.elf file and an Intel HEX file (*.hex). The correct file to upload to your device depends on the tool you use to do the programming. More information in the corresponding subsection.

This is always possible and you have two options in terms of what software to use:

TI’s SmartRF Flash Programmer 2. Windows only. Supports *.bin, *.elf and *.hex.
TI’s Uniflash. Linux, OS X and Windows. Supports *.bin, *.elf and *.hex.

Using the ROM bootloader

Under some circumstances, the device can also be programmed through its ROM bootloader, using the cc2538-bsl script under tools. This is commonly done using make <contiki-project>.upload (e.g. make hello-world.upload), which automatically invokes cc2538-bsl with the correct arguments.

This is currently only supported for the x0 devices of the family (cc26x0, cc13x0), but not for the newer x2 devices (e.g. cc1312r1 or cc1352p1).

Device Enumeration

LaunchPads and Sensortags use an XDS110 debugger, while the SmartRF06 EB uses an XDS100v3 debugger. If you are using a SmartRF06 EB, make sure the “Enable UART” jumper is set.

On Windows, you can view connected devices with Device Manager. Open up Device Manager and expand Ports (COM & LPT). You should observe various XDS debugger connections, depending on which boards are connected.

For an XDS110 debugger, two COM ports are available: an Application/User UART port and an Auxiliary Data port. For any serial connections, use the Application/User UART port.

For an XDS100v3 debugger, only a single USB Serial port is available. Use this port for any serial connections.

On Linux, XDS110 debuggers will show up under /dev as /dev/ttyACM*, while XDS100v3 will show up under /dev as /dev/ttyUSB*.

However, if the XDS100v3 debugger does not show up, you can manullay configure the device. First, find the BUS ID of the XDS100v3 debugger with lsusb.

$ lsusb
...
Bus 001 Device 002: ID 0403:a6d1 Future Technology Devices International, Ltd

The ID in this case is 0403:a6d1. Register this as a new FTDI ID with the ftdi_sio driver.

From kernel version 3.12 and newer:

# modprobe ftdi_sio
# echo 0403 a6d1 > /sys/bus/usb-serial/drivers/ftdi_sio/new_id

Before kernel version 3.12:

# modprobe ftdi_sio vendor=0x0403 product=0xa6d1

On OS X, the device will show up as /dev/tty.usbmodem<sequence of letters and numbers> (e.g. tty.usbmodemL1000191)

Conditions to use the ROM bootloader

On Linux and OS X, you can program your device via the chip’s serial ROM bootloader. In order for this to work, the following conditions need to be met:

The board supports the bootloader. This is the case for SmartRF06EB with CC13x0/CC26x0 EMs and it is also the case for LaunchPads. Note that uploading over serial does not (and will not) work for the Sensortag.
The ROM bootloader is unlocked.

You will not be able to use the ROM bootloader with a new out-of-the-box device programmed with factory firmware.

For newly-bought hardware, you need to use the JTAG to first erase the device using either SmartRF Flash Programmer 2 or UniFlash (see the relevant subsection).

After reset, the device will either execute the firmware on its flash or enter bootloader mode so it can be programmed. This is dictated by the following logic:

If the flash is empty, the device will enter bootloader mode and can be programmed using the ROM bootloader.
If the flash contains a firmware image:
- If the firmware is configured to lock the bootloader (which is the case e.g. for factory images), the device will execute the firmware and will not enter ROM bootloader mode.
- If the firmware is configured to unlock the bootloader, and if a specific (configurable) DIO pin is high/low (also configurable), the device will enter bootloader mode and can be programmed using the ROM bootloader.

To enable/unlock the bootloader backdoor in your image, define CCFG_CONF_ROM_BOOTLOADER_ENABLE as 1 in your application’s project-conf.h. The correct DIO and high/low state required to enter bootloader mode will be automatically configured for you, depending on your device.

With the above in mind, force your device into bootloader mode by keeping the correct user button pressed, and then pressing and releasing the reset button. On the SmartRF06EB, you enter the bootloader by resetting the EM (EM RESET button) while holding the select button. For the LaunchPad, you enter the bootloader by resetting the chip while holding BTN_1. It is possible to change the pin that will trigger bootloader mode by changing CCFG_CONF_BL_PIN_NUMBER in your application’s project-conf.h.

Remember that the device will always enter bootloader mode if you erase its flash contents.

If your device has correctly entered bootloader mode, you can now program it.

The serial uploader script will automatically pick the first available serial port. If this is not the port where your node is connected to, you can force the script to use a specific port by defining the PORT argument, e.g.:

$ make PORT=/dev/ttyACM0 hello-world.upload

If you get the error below, the most probable cause is that you have specified the wrong PORT, or the device has not entered bootloader mode:

Connecting to target...
ERROR: Timeout waiting for ACK/NACK after 'Synch (0x55 0x55)'
make: *** [hello-world.upload] Error 1

Some common causes why the device has not entered bootloader mode:

The device’s flash contains an image that was built with CCFG_CONF_ROM_BOOTLOADER_ENABLE defined as 0. In this case, you will need to use SmartRF Flash Programmer 2 or UniFlash to erase flash.
You programmed the device with firmware meant for a different device (e.g. you programmed a LaunchPad with an image built for a Sensortag). In this case, you will also need to use SmartRF Flash Programmer 2 or UniFlash to erase flash.
You reset the device without keeping the correct button pressed. Simply try again.

For more information on the serial bootloader, see its README under the tools/cc2538-bsl directory.

Building Deployment / Production Images

For deployment/production images, it is strongly recommended to:

Disable the ROM bootloader by defining CCFG_CONF_ROM_BOOTLOADER_ENABLE as 0. In doing so, it is impossible to enter bootloader mode unless one first erases the device’s flash.
Disable the JTAG interface, by defining CCFG_CONF_JTAG_INTERFACE_DISABLE as 0. In doing so, the only JTAG operation available will be a device forced mass erase (using SmartRF Flash Programmer 2 or UniFlash).

Both macros have default values set in cc13xx-cc26xx-conf.h, found under arch/cpu/simplelink-cc13xx-cc26xx/. You can override the defaults in your application’s project-conf.h.

If you do not follow these guidelines, an individual with physical access to your device may be able to read out its flash contents. This could give them access to your IP and it could also lead to a compromise of e.g. keys used for encryption.

Border Router over UART

The platform code can be used as a border router (SLIP over UART) via the rpl-border-router example. This example is expected to work off-the-shelf, without any modifications required.

slip-radio with 6lbr

The platform can also operate as a slip-radio over UART, to be used with 6lbr.

Similar to the border router, the example is expected to work off-the-shelf, without any modifications required.

2.4 GHz vs Sub-1 GHz operation

The platform supports both modes of operation, provided the chip also has the relevant capability. 2.4 GHz mode is sometimes called IEEE mode while Sub-1 GHz mode is sometimes called Prop mode, based on the respective RF commands used in the corresponding implementation.

If you specify nothing, the platform will default to Sub-1 GHz mode for CC13xx devices and 2.4 GHz mode for CC26xx devices. To force either mode, you need to set RF_CONF_MODE to the relevant RF_MODE_* in your application’s project-conf.h.

// For 2.4 GHz (IEEE) Mode
#define RF_CONF_MODE    RF_MODE_2_4_GHZ
// For Sub-1 GHz (Prop) Mode
#define RF_CONF_MODE    RF_MODE_SUB_1_GHZ

Low-Power Operation

The platform takes advantage of the Power driver, which is part of TI Drivers. In a nutshell, other TI Drivers will acquire and release certain power constraints, and the Power driver will seamlessly turn on/off power domains depending on what power constraints are set. When there are no events in the Contiki-NG event queue, the Power driver will put the CPU into the lowest possible power state.

Because this platform’s low-power operation is handled inside TI-provided drivers, the Contiki-NG energest module has no immediate way of determining the CPU’s power state with accuracy. More specifically, it is impossible to distinguish between ENERGEST_TYPE_LPM and ENERGEST_TYPE_DEEP_LPM. When using the energest module for this platform, the value of ENERGEST_TYPE_DEEP_LPM will always be zero; this is expected behaviour. All time spent by the CPU in any low-power mode will be captured under ENERGEST_TYPE_LPM.

SimpleLink Software Environment

The SimpleLink software environment is a collection of drivers (TI Drivers) and plugins, which are common across different SimpleLink device families. At the core of the SimpleLink platform, there is a Real-Time Operating System (RTOS), which provides services such as timing and scheduling tasks.

For Contiki-NG, the NoRTOS kernel is used. NoRTOS is a single-threaded RTOS which only implements bare-minimum RTOS primitives, such as timers and semaphores. NoRTOS is required for using TI Drivers. Interrupts will still preempt the main thread, but typical “multithreading” is not supported.

TI Drivers is a collection of drivers for a number of peripherals. Most drivers are common across several device families, while some are available only for certain families.

Plugins, or middleware, are components which add functionality on top of drivers, such as communication stacks and graphics libraries.

The SimpleLink software environment is packaged together in a Software Development Kit (SDK). SimpleLink SDKs can be downloaded for each SimpleLink device family, and are updated by TI in a quarterly manner. However, Contiki-NG provides a Core SDK, which is a SimpleLink SDK common for all CC13xx and CC26xx devices. The Core SDK is provided as a git submodule.

Override Core SDK

By default, the Core SDK will be used by the build system when building. However, you can override the Core SDK with a locally installed SimpleLink SDK by overriding the CORE_SDK environment variable. The variable must point to the full path of the installed SimpleLink SDK, as in the following example:

$ make CORE_SDK=/opt/ti/simplelink_cc26x2_sdk_2_30_00_34 TARGET=simplelink BOARD=launchpad/cc26x2r1

This allows you to update the Core SDK version to a newer version than what is provided by Contiki-NG.

However, there are some limitations you need to be aware of when overriding the Core SDK. There is no good way to determine the minimal SimpleLink SDK version which is compatible with the Contiki-NG version you are working with. This comes from the fact that the SimpleLink SDKs are updated at a faster rate by TI than what Contiki-NG updates the Core SDK submodule.

In addition, the SimpleLink SDK must also correspond to the board you are compiling for. For example, if you are overriding the Core SDK with a SimpleLink CC26x2 SDK, then you must use a CC26x2 device, such as the CC26x2R1 LaunchPad.

Configure TI Drivers

Some of the TI drivers are partially integrated with the Contiki-NG environment, and therefore has to be initialized by the Contiki-NG run-time if used. In order to make this configurable, certain drivers can be enabled or disabled by setting a configuration define in your application’s project-conf.h. Enabling or disabling a driver means in this context whether the Contiki-NG run-time should initialize the driver at run-time.

Below is a summary of which TI drivers can be configured with which configuration defines, and what the default value of the configuration defines are.

TI Driver	Configuration Define	Default Value
UART	`TI_UART_CONF_ENABLE`	1
SPI	`TI_SPI_CONF_ENABLE`	1
I2C	`TI_I2C_CONF_ENABLE`	1
NVS	`TI_NVS_CONF_ENABLE`	0
SD	`TI_SD_CONF_ENABLE`	0

Disabling unused drivers are beneficial, as it reduces code and memory footprint. However, some features may depend on certain drivers, and disabling a driver which some other drivers depend on will result in a compile error. For example, the Sensortag sensor drivers use the I2C driver, and therefore disabling the I2C driver requires Board sensors to be disabled as well.

Some of the drivers have multiple peripherals, which can be independently enabled or disabled. This is done purely for reducing the memory footprint, as the compiler is not able to optimize and remove unused peripherals when a driver is enabled.

In other words, enabling the SPI driver with both peripherals but only using the SPI0 peripheral, you still have to have the SPI1 peripheral configuration objects in memory.

Peripheral	Configuration Define	Default Value	CC13x0/CC26x0	CC13x2/CC26x2
UART0	`TI_UART_CONF_UART0_ENABLE`	`TI_UART_CONF_ENABLE`	Yes	Yes
UART1	`TI_UART_CONF_UART1_ENABLE`	0	Yes	Yes
SPI0	`TI_SPI_CONF_SPI0_ENABLE`	`TI_SPI_CONF_ENABLE`	Yes	Yes
SPI1	`TI_SPI_CONF_SPI1_ENABLE`	0	No	Yes
I2C0	`TI_I2C_CONF_I2C0_ENABLE`	`TI_I2C_CONF_ENABLE`	Yes	Yes
NVS Internal	`TI_NVS_CONF_NVS_INTERNAL_ENABLE`	`TI_NVS_CONF_ENABLE`	Yes	Yes
NVS External	`TI_NVS_CONF_NVS_EXTERNAL_ENABLE`	`TI_NVS_CONF_ENABLE`	Yes	Yes

Any other TI Driver, except for the RF driver, can be used as normal.

SimpleLink Support

Any issues regarding TI software from the SimpleLink SDK, or any issues regarding the software implementation of this platform, please post to the E2E forum.

For any issues regarding Contiki-NG in general that is not directly relevant to the software implementation of this platform, please post an issue to the Contiki-NG repository.

Set up Contiki-NG in Code Composer Studio

Before anything else, make sure you have cloned out the Contiki-NG repository and at least checked out the coresdk_cc13xx_cc26xx and CMSIS submodules.

$ git clone https://github.com/contiki-ng/contiki-ng.git
$ cd contiki-ng
$ git submodule update --init arch/cpu/simplelink-cc13xx-cc26xx/lib/coresdk_cc13xx_cc26xx arch/cpu/arm/CMSIS

Download the necessary software:

TI’s Code Composer Studio (CCS) with support for CC13xx/CC26xx devices installed.
The ARM GCC add-on in CCS. In CCS:
- View → CCS App Center.
- Search for ARM GCC and click Select.
If you are using Windows:
- Install Git for Windows.
If you are using Linux:
- sudo apt-get install build-essential

Note that when debugging CC13x0 and CC26x0 devices with CCS, the Watchdog module should be disabled (unless you are debugging Watchdog usage). The Watchdog on CC13x0 and CC26x0 devices is not properly paused when halted by the debugger, and therefore causes an unexpected system reset which breaks the debugging session. The Watchdog module is disabled by setting WATCHDOG_CONF_DISABLE to 1 in your application’s project-conf.h file.

In CCS, do the following steps:

Create an empty CCS project. In CCS:
- File → New → CCS Project.
- Set Target to SimpleLink Wireless MCU and Target device to your device.
- Name the project to your liking.
- Make sure the Compiler version is set to GNU compiler.
- Select the Empty Project template.
- Click Finish.
Add a path variable for Contiki-NG. This is only for convenience, as this allows us to refer to the Contiki-NG source folder later. In CCS:
- In Project Explorer, right click the project → Properties.
- Resource → Linked Resources.
- Click New.
- Set Name to CONTIKI_ROOT.
- Set Location to the path of the Contiki-NG repository. You can click Folder and manually select the relevant folder.
Add Contiki-NG source folders to the project. This allows you to browse Contiki-NG source files in CCS without copying them into the project folder. In CCS:
- In Project Explorer, right click the project → New → Folder.
- Set Folder name to contiki-ng.
- Click Advanced.
- Select Link to alternate location (Linked Folder).
- In the textbox, write ${CONTIKI_ROOT}.
- Click Finish.
- Click No if CCS asks to include .cfg files, as CCS is interpreting them as XDCTools configuration files.
Windows only: Add Git for Windows and SRecord to the PATH environment variable in the CCS project. The Contiki-NG build system needs other shell tools such as git and make from Git for Windows and the srec_cat tool from the SRecord package. In CCS:
- In Project Explorer, right click the project → Properties.
- CCS Build → Environment.
- If the PATH variable does not exist, click Add, set Name to PATH and Value to ${Path}.
- Select the PATH variable and click Edit.
- Prepend the absolute path of both the bin and usr\bin folders from the Git for Windows installation and the absolute path of the SRecord folder from the SRecord package extraction to the PATH variable.
  - Separate paths with ;.
  - For example, if the installation path for Git for Windows is C:\Git and the extraction path for SRecord is C:\SRecord, then prepend C:\Git\bin;C:\Git\usr\bin;C:\SRecord; to the PATH variable.
- Click OK.
Adjust build settings to correctly invoke the Contiki-NG Makefile. In CCS:
- In Project Explorer, right click the project → Properties.
- Make sure Show advanced settings (in the bottom left corner) is clicked.
- CCS Build → Builder.
- Unselect Generate Makefiles automatically.
- Under Build location, set Build directory to the project directory of your application.
  - For building a Contiki-NG example, use the source directory of the example (e.g. ${CONTIKI_ROOT}/examples/hello-world).
  - For building your own applications, put the application sources and the Makefile into your project directory, not in the Contiki-NG directory.
- Under Make build targets;
  - Unselect Build on resource save (Auto build).
  - Select Build (Incremental build) and set it to <contiki-project> (e.g. hello-world) assigned in the project Makefile.
  - Select Clean and set it to clean.
Add the TARGET and BOARD variables, and add debug symbols:
- In the project Makefile, add the following lines:
  - Set TARGET to simplelink, i.e.:
    TARGET = simplelink
  - Set BOARD to the device you want to compile for, e.g.:
    BOARD = launchpad/cc1310
  - Set DEBUG to 1 to enable debug symbols.
    DEBUG = 1
Build the project. In CCS:
- In Project Explorer, right click the project → Build Project.
- If something goes wrong, it is usually due to tools not being found. Check the PATH environment variable in that case.
Create and configure a debug session. In CCS:
- Start by creating a default debug session.
  - In Project Explorer, right click the project → Debug As → Code Composer Debug Session.
  - This is expected to fail, because the path of the executable file guessed by CCS is wrong.
- Set the correct path.
  - In Project Explorer, right click the project → Properties.
  - Select Run/Debug Settings.
  - Select the newly created launch session with the same name as the project and click Edit.
  - Under Program, set Program to the absolute path of the generated *.elf file. It is recommended to click File System and select the *.elf file manually to make sure the path is correct.
- Start debugging.
  - In Project Explorer, right click the project → Debug As → Code Composer Debug Session.
  - The debug session should start as intended, and you should be able to step through the source code.

In order to view the serial output of the device connected to PORT, via Terminal in CCS:

View → Terminal.
Open a Terminal by clicking the designated icon.
Set Choose terminal to Serial Terminal and Serial port to the right PORT.
Click OK.

Note: You will most likely see that the new line character (\n) in the output is interpreted as LF instead of CRLF. This misinterpretation is a known problem for which no solution has been provided so far. An indirect solution for this problem is to insert a carriage return character (\r) before a new line one. One way to do so is to modify contiki-ng/arch/cpu/simplelink-cc13xx-cc26xx/dev/dbg-arch.c as follows:

  75           return 0;
  76         }
  77
  +    /* Find the number of new line characters in the sequence. */
  +    size_t n = 0;
  +    for(size_t i = 0; i < max_len; i++)
  +      if(*(seq + i) == '\n')
  +        ++n;
  +
  +    if(n > 0) {
  +      /*
  +       * Create the second sequence by inserting a carriage return character
  +       * before any new line one in the first sequence.
  +       */
  +      unsigned char ch, seq2[max_len + n];
  +      size_t j = 0;
  +      for(size_t i = 0; i < max_len; i++) {
  +        ch = *(seq + i);
  +        if(ch != '\n')
  +          seq2[j] = ch;
  +        else {
  +          seq2[j] = '\r';
  +          seq2[++j] = '\n';
  +        }
  +        ++j;
  +      }
  +      num_bytes = (int)uart0_write((const unsigned char *)seq2, max_len + n);
  +    }
  +    else
        -    num_bytes = (int)uart0_write(seq, max_len);
  +      num_bytes = (int)uart0_write(seq, max_len);
  +    
 106         return (num_bytes > 0)
 107                ? num_bytes
 108                : 0;

Note that the above modification results in increased stack memory usage which, in turn, increases the probability of stack memory overflow. There might be alternative solutions, especially direct ones that might be provided by the Eclipse/CCS community in the future.