Texas Instruments MSPM0 User manual

User’s Guide

MSPM0 Bootloader

ABSTRACT

The MSPM0 Bootloader (also known as BSL) provides a method to program and verify the device memory

(Flash and RAM) through a standard serial interface (UART or I2C).

Table of Contents

1 Overview of BSL Features..................................................................................................................................................... 2

2 Terminology.............................................................................................................................................................................3

3 BSL Architecture.....................................................................................................................................................................4

3.1 Design................................................................................................................................................................................ 4

3.2 BSL Invocation................................................................................................................................................................... 5

3.3 Memory.............................................................................................................................................................................. 6

3.4 BSL Configuration.............................................................................................................................................................. 7

3.5 BSL Status......................................................................................................................................................................... 8

4 Bootloader Protocol............................................................................................................................................................... 9

4.1 Packet Format....................................................................................................................................................................9

4.2 UART and I2C BSL Protocol..............................................................................................................................................9

4.3 Bootloader Core Commands............................................................................................................................................10

4.4 BSL Core Response........................................................................................................................................................ 18

4.5 Bootloader Security..........................................................................................................................................................20

5 Sample Program Flow with Bootloader..............................................................................................................................22

6 Secondary Bootloader..........................................................................................................................................................24

6.1 Secondary Bootloader Example.......................................................................................................................................24

7 Interface Plug-in....................................................................................................................................................................26

7.1 Implementation.................................................................................................................................................................26

7.2 Flash Plug-in Type........................................................................................................................................................... 28

7.3 Overriding an Existing Interface....................................................................................................................................... 29

8 References............................................................................................................................................................................ 31

9 Revision History................................................................................................................................................................... 31

Trademarks

All trademarks are the property of their respective owners.

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1 Overview of BSL Features

The bootstrap loader (BSL) provides a method to program or verify the device memory through a standard

UART or I2C serial interface.

Key features of the BSL that are accessible through the serial interface include:

• Programming and erase of flash memory

• Can return a 32-bit CRC of a code or data region (1KB minimum region size) to verify programming

• Can enable code or data read-out (disabled by default)

• Can return a firmware version number via a pointer to the main flash

• Can specify a hardware invoke GPIO

• Access is always protected with a 256-bit password

• Configurable security alert handling for resisting brute force attacks

• Can add a new interface as flash plug-in

• Can use custom bootloader

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2 Terminology

Bootloader (BSL) - Boot routine used to load data to the device memory

Bootcode (BCR) - Startup Routine that runs after BOOTRST, to configure the device for executing application

BCR configuration - Configuration structure that contains all user configurable parameters for Bootcode, which

resides in Non-main flash memory

BSL configuration - Configuration structure that contains all user configurable parameters for Bootloader, which

resides in Non-main flash memory

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3 BSL Architecture

3.1 Design

The bootloader will be invoked by bootcode when a valid bootloader invocation condition is detected. It will be

invoked only if the bootloader is enabled in the BSL mode field of the BCR configuration.

Once the bootloader is started, it first executes the "Init" phase where the initial checks of the BSL configuration

is done and the device is configured for bootloader operations.

Next the bootloader enters "Interface Autodetection" phase. In this phase the BSL configures all the available

BSL ROM interfaces and the flash plug-in interface , if registered . The BSL then polls for the data through all

the interfaces one by one. When a valid connection packet is received in one of the interfaces, that interface will

be considered as active interface for further communication and all other interfaces will be disabled. Interface

discovery is done for 10 seconds, if no interface has been detected, the device is put in STANDBY mode.

Next the BSL enters "Command reception" phase. In this phase BSL will be waiting in an infinite loop for

commands from the host. When a valid command is received, the command is processed and the response from

the BSL core is sent back to the host. Then it goes back to the loop and waits for the next command and so on.

If the 'Start Application' command is received, the bootloader will trigger a system reset, after which the bootcode

is executed and the application is invoked. This phase also has a timeout of 10 seconds. If there is no valid

command received, bootloader is locked and it enters Sleep mode.

Figure 3-1. BSL Architecture

3.1.1 Timeout Feature

Bootloader will time out when no activity is detected and enters low-power mode to save power.

This has been implemented at the following two phases.

1. Interface autodetection

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2. Command reception

3.1.1.1 Interface Autodetection

In Interface detection phase, if there is no valid connection command received for 10 seconds over any interface,

the bootloader enters STANDBY mode.

POR is required to get out of this state and use Bootloader by creating the BSL invocation condition again.

3.1.1.2 Command Reception

In command reception phase, if no valid command is received for 10 seconds, the bootloader will enter SLEEP

mode. To wake up the device from SLEEP mode, a data transaction should happen on the active interface.

Bootloader will be locked before entering Sleep mode to reduce attack surface. Hence after waking up from the

low power mode, Bootloader needs to be unlocked again by sending the 256 bit BSL Password (See Unlock

Bootloader command ).

Note

Bootloader user LFCLK for the timeout check. If application configures the external clock as the

source for LFCLK, the same will be used by BSL, when invoked through Application BSL request

3.2 BSL Invocation

Bootloader shall be invoked only by the boot code, when any of the BSL invocation conditions is met and if

Bootloader is enabled in BCR configuration TRM.

When Fast boot mode is enabled in BCR configuration, bootloader can be invoked only by Debug mailbox

command and Application request. Other checks are skipped to save execution time.

3.2.1 Blank Device

Bootcode detects the blank device by checking the erase state of the Stack pointer (0x00000000) and reset

vector (0x00000004) address. When both the flash memory addresses are found to be blank, then Bootloader

will be invoked.

3.2.2 Application Request

To invoke the bootloader from an application, set the RESETLEVEL as BOOTLOADERENTRY and trigger reset

through the RESETCMD register. This sequence causes a system reset, and the bootcode is executed and the

bootloader is invoked.

Because a system reset is issued, all the peripheral configurations are reset while exiting the application.

3.2.3 GPIO Based Invocation

GPIO used for BSL invocation can be configured in the BSL Configuration TRM in Non-main memory.

Fresh devices will have the TI programmed default pin detail in BSL configuration.

GPIO pin based invocation can be disabled in the BCR configuration. It is enabled by default.

GPIO should be asserted before the POR, and the state should be maintained for at-least T_start ms after POR.

Then the GPIO pin state can be de-asserted.

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Figure 3-2. Invocation From GPIO

* - GPIO pin to be used as 'BSL Invoke' and 'Expected Pin Level' can be configured in BSL configuration

** - T_start refers to the Cold boot startup time, specified in the device specific data sheet

Note

If pin based BSL invocation is enabled, the configured GPIO pin should be either pulled high or low. It

should not be left floating, which could cause unexpected BSL execution.

3.2.4 Debug Mailbox Command

When debug interface is available, Bootloader invocation command can be sent through the Debug Subsystem

Mailbox (DSSM).

For more details on the DSSM command usage, please refer to MSPM0x_Technical_Reference_Manual DSSM

commands section.

3.2.5 Others

3.2.5.1 Pre-Boot Application Verification

In the BCR configuration, if application CRC verification is enabled TRM, the bootcode verifies the CRC for the

given application memory range. If the CRC is incorrect, the bootloader is invoked. In this case the bootloader is

invoked only if enabled. Otherwise the bootcode logs a catastrophic error and causes boot failure.

3.3 Memory

3.3.1 SRAM Memory Usage

The SRAM Memory layout explains the memory used for bootloader's operation.

• Data and Stack section - Used by BSL for it's operation. While exiting the bootloader, these sections of the

SRAM are cleared.

• Variable Buffer Space - Buffer space used for storing the data packets received /sent during the BSL

communication

The SRAM memory allowed for read and write access by the host is BSL Buffer Start Address to [SRAM end

address - 0x120], where SRAM end address is determined by the SRAM memory available in each device.

Since the same SRAM space is shared with variable buffer space, it has chances of getting overwritten during

an SRAM write/read operation.

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Figure 3-3. SRAM Usage

A - SRAM Start Address (0x20000000)

B- 'BSL Buffer Start Address' known from the 'Get Device Info' command response, when no Flash plug-in

interface is registered

C- 'BSL Buffer Start Address' known from the 'Get Device Info' command response. It will be same as 'B' when

no Flash plug-in interface is registered

D- BSL Buffer End Address ='BSL Buffer Start Address' + (2 * 'BSL Max Buffer size'), where BSL Buffer Start

Address and BSL Max Buffer Size can be known from 'Get Device Info' command response

E- Start address of the stack allocation (E - 0x120). It will be same as 'D' when the 'BSL Max Buffer size' is less

than 0xFFFF

F- End address of the SRAM memory available in the device. Refer to device specific data sheet to know this.

Section B- C :

• Data section that will be allocated for Flash Plug-in operation, when registered in BSL configuration

Section C- D:

• Buffer space used to store data packets

• Maximum size is (2 * 0xFFFF)

Section C-E:

• Available memory for SRAM read and write operation through BSL commands

3.4 BSL Configuration

BSL configuration in Non-main Flash memory allows certain parameters used by BSL to be customized by the

user.

To know more about the available configurations, refer MSPM0 Technical Reference Manual - Configuration

Memory section .

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3.5 BSL Status

BSL status gives the details about any error occurred during the execution, that resulted in unresponsive BSL.

This 32-bit status information is stored in a specific SRAM address (0x200000C0), and can be read through the

debugger, if the debug-access is enabled in the BCR configuration.

Table 3-1. Interpretation of BSL Status

Byte 4 Byte 3 Byte 2 Byte 1

Reserved HW Error HW Error details SW Error

SW Error

Error Description

0x01 BSL Configuration CRC Error

HW Error

Error Description HW Error Details

0x07 NMI exception NMIIDX - NMI Interrupt Index register data

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4 Bootloader Protocol

4.1 Packet Format

The BSL data packet has a layered structure. The BSL core command contains the actual command data to be

processed by the BSL. In addition to the standard BSL commands, there can be wrapper data before and after

each core command known as the peripheral interface code (PI Code). This wrapper data is information that is

specific to the peripheral and protocol being used, and it contains information that allows for correct transmission

of the BSL core command. Taken together, the wrapper and core command constitute a BSL data packet

PI Code BSL Core Data PI Code

4.2 UART and I2C BSL Protocol

The data packets of the UART and I2C BSL protocol have the following structure.

• Header byte indicates the protocol used and the packet type (command or response packet).

• Length field contains the size of the BSL Core Data in bytes.

• BSL core data, contains the Command / Response ID and Address, data as needed by the command

• CRC32 field contains the CRC calculated for the data in BSL core data

PI Code BSL Core Data PI Code

Header (1 byte) Length (2 byte) BSL Core Command/Response CRC32 (4 byte)

Based on the Core data field, the data packet is classified as either Command packet or response packet.

Command packet is the first packet which is transmitted to the BSL. The second packet is the Response packet

which is received from the BSL. Response packet contains two components BSL acknowledgment and BSL

Core response. In these two, Acknowledgment is received from BSL for every command packet sent. But the

BSL core response is not received for every command.

Figure 4-1. BSL Protocol

4.2.1 BSL Acknowledgment

The peripheral interface section of the BSL software parses the wrapper section of the BSL data packet. If there

are errors with the data transmission, an error message is sent immediately. An ACK is sent after all data has

been successfully received and does not mean that the command has been correctly executed (or even that the

command was valid) but, rather, that the data packet was formatted correctly and passed on to the BSL core

software for interpretation.

The BSL protocol dictates that every BSL data packet sent is responded to with a single byte acknowledgment

in addition to any BSL data packets that are sent. Table lists the acknowledgment responses from the BSL.

If an acknowledgment byte other than ACK is sent, the BSL does not send any BSL data packets. The host

programmer must check the acknowledgment error and retry transmission.

Data Meaning

0x00 BSL_ACK (Packet received successfully)

0x51 BSL_ERROR_HEADER_INCORRECT

0x52 BSL_ERROR_CHECKSUM_INCORRECT

0x53 BSL_ERROR_PACKET_SIZE_ZERO

0x54 BSL_ERROR_PACKET_SIZE_TOO_BIG

0x55 BSL_ERROR_UNKNOWN_ERROR

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Data Meaning

0x56 BSL_ERROR_UNKNOWN_BAUD_RATE

4.2.2 Peripheral Configuration

4.2.2.1 UART

UART is enabled with following configuration:

• UART0 is used

• Baud rate 9600 bps by default. It can be updated by Change Baud Rate command

• Data width: 8 bit

• Stop bits: 1

• No parity

• Pins used for RXD and TXD are taken from the BSL configuration

4.2.2.2 I2C

The I2C interface in the BSL can act as the I2C target. The host acts as a controller and drives the

communication.

• I2C0 is used

• The I2C target address is 0x48, by default. It can be configured in BSL Configuration

• External pullup is needed for SCL and SDA lines

• Pins used for SDA and SCL are taken from the BSL configuration

Note

• The BSL does not validate the details of the pins configured in the non-main for the UART and I2C

interfaces. The BSL expects the pin configuration to be correct.

• Do not use the same pins for both UART and I2C.

4.2.2.3 CRC

CRC for the data must be calculated with:

• CRC32-ISO3309 polynomial

• Bit reversed configuration

• Initial seed - 0xFFFFFFFF

4.3 Bootloader Core Commands

BSL Command Protected CMD Start Address Data (Bytes) BSL Core response

CMD Connection No 0x12 - - No

CMD Unlock

Bootloader No 0x21 - D1…D32 (Password) Yes

CMD Flash Range

Erase Yes 0x23 A1...A4 A1...A4 (End address) Yes

CMD Mass Erase Yes 0x15 - - Yes

CMD Program Data Yes 0x20 A1...A4 D1…Dn, Yes

CMD Program Data

Fast Yes 0x24 A1...A4 D1…Dn, No

CMD Memory Read

back Yes 0x29 A1...A4 L1...L4 Yes

CMD Factory Reset Yes 0x30 - D1...D16 (Password) Yes

CMD Get Device

Info No 0x19 - - Yes

CMD Standalone

Verification Yes 0x26 A1...A4 L1...L4 Yes

CMD Start application No 0x40 - - No

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