Bootloader Design Techniques for Microcontrollers

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1 Bootloader Design Techniques for Microcontrollers Jacob Beningo Beningo Embedded Group

2 Speaker/Author Details : jacob@beningo.com : : Jacob_Beningo : Beningo Engineering : JacobBeningo : Embedded Basics Embedded Bytes Newsletter

3 Design News CEC Courses Overview CEC CEC Side Topics 2017 Fundamentals of Embedded Software (2013) Mastering the Software Design Cycle (2014) Python for Embedded Systems(2014) Software Architecture Design (2014) Bootloader Design for MCUs (2016) Rapid Prototyping w/ Micro Python (2016) Debugging (2016) Professional Firmware (2016) API s and HAL s February 2017 Baremetalto RTOS April 2017 Designing IoT Sensor Nodes July 2017 From C to C++ October 2017 Real-Time Software using Micro Python Embedded Bytes Newsletter Baremetal C (2015) Mastering the ARM Cortex- M Processor (2015) Writing Portable and Robust Firmware in C (2015) Design Patterns and the Internet (2015)

4 Session Overview Bootloader Models and Concepts Application Branching Bootloader Implementation Bootloader Commands Image Assembly Communication Protocol Design Setting up a Test Application Troubleshooting Techniques 4

5 Why do I need a bootloader? 5

6 What is a bootloader? Environment MCU 6

7 Where do bootloaders come from? Silicon Vendors 3 rd Party Open Source Roll your own 7

8 DfuSe Utility 8

9 Bootloader Models Single MCU System (Traditional / Most Common) Flashing Method Laptop / Workstation Tablet or mobile device USB Flash System 9

10 Bootloader Models Multi MCU System (Not as common or traditional) Flashing Method Laptop / Workstation Master MCU Can be updated itself Passes new application to slave devices and acts as the flash tool Tablet or mobile device USB Flash System 10

11 Bootloader Models MCU System Single MCU Devices Multi MCU Devices Systems are internet enabled Physical Separation from imaging tool Flashing Method Internet Connected Devices Tablets Phones Computers 11

12 Bootloader Models MCU System Single MCU Devices Multi MCU Devices Systems are not internet enabled Physical Separation from imaging tool Flashing Method Internet Connected Devices Tablets Phones Computers 12

13 Bootloader Models MCU System Single MCU Devices Multi MCU Devices Systems are internet enabled Physical Separation from imaging tool Flashing Method Automated web services 13

14 Which model is right for you? 14

new firmware and manage its own flashing process Commands from an external source would not be required

15 Bootloader Update Process There are two behavioral models for the update process 1) Boot-loading process is completely automated and self-contained within the system boot-loader would automatically detect the new firmware and manage its own flashing process Commands from an external source would not be required to successfully carry out the bootloading process Ex. SD card boot-loader, web based automated update, etc 15

Bootloader Update Process There are two behavioral models for the update process 2) Boot-loading process is not self-contained but initializes into an idle state and awaits instructions

16 Bootloader Update Process There are two behavioral models for the update process 2) Boot-loading process is not self-contained but initializes into an idle state and awaits instructions from an outside source a pc based software application commands the boot-loader into the different states necessary to flash a new image onto the system Ex. CAN, UART, USB boot-loader 16

17 The Bootloader System 17

18 The Bootloader System 18

19 Setting up the linker 19

20 Setting up the linker 20

21 The Bootloader System 21

22 Startup Branching Advantages Code can be in assembly Branch is executed quickly Very simple implementation Disadvantages Susceptibility to start-up noise Dedicated GPIO Accidental bootloader entry 22

23 Startup Branching Example: brclr $0259, $01, GoBoot ; if PP0 == 0 then start the boot-loader ; if PP0 == 1 then start the application ldd AppResetVect ; Load the Application Reset Vector ldx AppResetVect jmp 0,x ; jump to the application GoBoot: lds #StackTop jmp main ; 23

24 Startup Branching What is the potential flaw with the previous branch code? 24

25 Startup Branching Example: Checking the reset vector brclr $0259, $01, GoBoot ; if PP0 == 0 then start the boot-loader ; if PP0 == 1 then start the application ldd AppResetVect ; Load the Application Reset Vector cpd #$ffff ; Compare it to 0xFFFF beq _GoBoot ; if the application reset vector is not ; available then start the bootloader ldx AppResetVect jmp 0,x ; jump to the application _GoBoot: lds #StackTop jmp main ; Continue Boot-loader startup 25

26 Startup Branching Example Advanced Check ldd AppResetVect ; Load the Application Reset Vector cpd #$ffff ; Compare it to 0xFFFF beq _GoBoot ; if the application reset vector is not ; available then start the bootloader ldd EepromProgStatus ; Read the programmed status byte from eeprom cpd # B ; Compare it to B for boot-load beq _GoBoot ; if Status == B for Boot-loader then jump to ; boot-loader, otherwise continue to the application ldx AppResetVect jmp 0,x ; jump to the application _GoBoot: lds #StackTop jmp main ; Continue Boot-loader startup 26

27 Startup Branching Integrating the branch code and the bootloader 27

28 Startup Checks 28

29 Startup Checks Branch Code in C if((checksum_complete == TRUE) && (StartUpTmr == EXPIRED)) { if((*resetvector!= 0xFFFF) && /* Does app reset vector exist? */ (Status!= 'B') && /* EEPROM status set? */ (Boot_ToolPresent!= TRUE) && /* Tool present? */ (Checksum_Valid!= FALSE)) /* Checksum valid? */ { App_LoadImage(); } else { Boot_LoadImage(); } } 29

30 Questions? 30

31 The Bootloader System 31

32 Bootloader Components 32

33 Application Components 33

34 Project Organization 34

35 API s Purpose simplify application programming by abstracting the application into black boxes. Critical to creating reusable software Defines a common interface that can be used from one project to the next 35

36 Creating a HAL Steps to develop a HAL for the peripheral Review the microcontroller peripheral Identify peripheral features Identify common MCU elements Identify non-standard MCU elements Design and Create the API Interface Create stubs and documentation templates Implement for Target processor(s) Test Repeat for next peripheral 36

37 Example HAL Interface 37

38 Accessing Flash What mode? Bit Page sector What should the API look like? 38

39 Accessing Flash 39

40 Accessing Flash 40

41 Command Parsing General Message Format Start Message (8 bits) OPCODE (8 bits) Data Length (8 bits) Data (x bytes) Checksum (16 bits) Checksum Fletcher16 (Approaches error detection of CRC) 41

42 Command Parsing OPCODE Command Description 0x30 Bootloader Enter This command is used to put the system into bootloader mode. 0x31 Bootloader Exit Used to exit the bootloader with the intention of entering the application code. 0x32 Device Erase Erases the application buffer space and prepares for receipt of new application code. 0x33 Device Program S-Record to program to the application buffer space. 0x34 Device Secure Secures the flash space from being read and written 0x35 Device Unsecure Unsecure the flash space for writing and reading. 0x36 Query Device Used to determine if the system is in bootloader or application mode. 42

43 Command Parsing 43

44 Command Parsing 44

45 Command Parsing 45

46 Command Parsing 46

47 Command Parsing - Message Packet Format Best Practices Use a packet format Use a checksum or CRC Track record packet numbers Use ACK and NAK for each packet Create specific error codes Don t assume that errors rarely happen Use 32 bit addressing as a default Include response timeout 47

48 Assembling the Image Requirements Command driven vs image driven Commands Lock/Unlock Flash Read/Write Configuration Image/Record Data Switch to Application Image Driven Continuously loops through image Completely Autonomous 48

need to be reassembled and validity checked Steps Receive image packets

49 Assembling the Image A block of image data is usually larger than can be directly communicated Memory region broken up into separate packets Packets need to be reassembled and validity checked Steps Receive image packets Reassemble into image block Verify Checksum Write Acknowledge Repeat until completed 49

50 Assembling the Image 50

51 The Bootloader System 51

$software reset Notify user to power cycle void Wdt_Reset(void) { } /* Enter an invalid key to force reset */ SWT.SR.$

52 Resetting the System How to reset the system Watchdog timer Infinite loop Illegal write to register Soft reset command Manual software reset Notify user to power cycle void Wdt_Reset(void) { } /* Enter an invalid key to force reset */ SWT.SR.R = 0x0000FFFF; 52

53 Bootloader Development What is needed for a test application? 53

54 Bootloader Development 54

55 Questions? 55

56 The Graphical User Interface 56

Application Storage Format https://en.wikipedia.

57 Application Storage Format CC BY-SA 3.0 Split in half to fit on slides in a legible fashion 57

58 Application Storage Format CC BY-SA 3.0 Split in half to fit on slides in a legible fashion 58

59 Application Storage Format CC BY-SA 3.0 Split in half to fit on slides in a legible fashion 59

60 Application Storage Format 1) 2) Record Count Address Data Checksum 60

61 Converting Application Formats Some IDEs only put out one record format! Useful format converter Hex2bin ( Bin2Srec ( Many other tools 61

62 Converting Application Formats 62

63 Converting Application Formats Hex2bin hex2bin filename 63

64 Converting Application Formats Bin2Srec Bin2srec a 4 o 0x input_filename > output_filename 64

65 Debugging Bootloaders What could possibly go wrong? 65

66 Debugging Two Applications Steps to debug the application: Run the boot-loader in debug Flash the application image onto the system Reset the processor Add symbols from the IDE and select the application symbols 66

67 Issues with Flash Flash controller NOT initialized properly Clock rate Clock gating Write method Byte or Page? Checksum Wrong place Written backwards Not written! 67

68 Resolutions for Flash Write a test harness to verify flash settings and write to various locations in flash Flash driver should Write record to flash Verify write by reading back and comparing Failure to write should generate an error! Use example code for flash as a jumping off point for your own driver 68

69 Image Verification Export the flash image from the IDE while in debug mode running only the application Export the flash image from the IDE while in debug mode running the boot-loader with the application Use WinMerge to compare the images to determine if there is a difference between the image when loaded through the bootloader 69

70 Valid Reset Vector? One of the major causes of staying in the bootloader 70

71 C Copy Down Is the C copy down being performed? 71

72 Write Once Registers Are any write-once registers trying to be written by both the boot-loader and the application? Watchdog Timers Processor Mode registers Memory registers 72

73 Example Test Cases 73

74 Example Test Cases 74

75 Example Test Cases 75

76 Best Practices Test the corner cases Use a test harness Don t be shy when it comes to error codes Use assertions Start with a simple test application Leverage example code but build in robustness 76

77 Bootloader Fall Backs 77

78 Where to go from here? Encryption Authentication Relocatable applications GUI Investigations Write your own 78

Additional Resources Download Course Material for Updated C Doxygen Templates (Sept 2015) Example source code Bootloader White Paper Templates Microcontroller API

79 Additional Resources Download Course Material for Updated C Doxygen Templates (Sept 2015) Example source code Bootloader White Paper Templates Microcontroller API Standard EDN Embedded Basics Articles Embedded Bytes Newsletter From under - Blog and Articles > Software Techniques > CEC Bootloader Design for MCUs

80 Thank You! f

Bootloader Design Techniques for MCUs. Jacob Beningo, CSDP

Bootloader Design Techniques for MCUs Jacob Beningo, CSDP 1 10/18/2014 Session Overview Introduction The Boot-loader System Local Models Distributed Models Startup Branching Bootloader Behavior Resetting