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kotlin-library

README.md

GBL-Ninja Library

Kotlin library for parsing and creating files in the GBL (Gecko Bootloader) format. This library provides a comprehensive API for working with GBL files used in Silicon Labs firmware updates.

Features

  • Parse GBL files into structured objects
  • Create new GBL files from scratch
  • Modify existing tag contents
  • Validate file integrity with automatic CRC verification
  • Support for all standard GBL tag types
  • Compression support for LZ4 and LZMA
  • Security features including ECDSA signatures and encryption
  • Container system for advanced tag management
  • Serialization to JSON for storage and transfer

Installation

Gradle (Kotlin DSL):

dependencies {
    implementation(files("libs/gbl-ninja-kotlin.jar"))
}

Steps:

  1. Download the latest gbl-ninja-kotlin.jar from the releases
  2. Place it in your project's libs/ directory
  3. Add the dependency to your build.gradle.kts

Quick Start

Parsing a GBL File

val gblParser = Gbl()

val file = File("firmware.gbl")
val byteArray = file.readBytes()

val parseResult = gblParser.parseByteArray(byteArray)

when (parseResult) {
    is ParseResult.Success -> {
        val tags = parseResult.resultList
        println("Successfully parsed ${tags.size} tags")
        tags.forEach { tag ->
            println("Tag: ${tag.tagType}, Size: ${tag.content().size} bytes")
        }
    }
    is ParseResult.Fatal -> {
        println("Error parsing file: ${parseResult.error}")
    }
}

Creating a New GBL File

val gblBuilder = Gbl.GblBuilder.create()
    .application(
        type = 32U,
        version = 0x10000U,
        capabilities = 0U,
        productId = 54U
    )
    .prog(
        flashStartAddress = 0x1000U, 
        data = firmwareData
    )

val gblBytes = gblBuilder.buildToByteArray()
File("new_firmware.gbl").writeBytes(gblBytes)

Advanced: Creating GBL with Security

val certificate = ApplicationCertificate(
    structVersion = 1U,
    flags = 0U,
    key = 0U,
    version = 1U,
    signature = 0U
)

val gblBuilder = Gbl.GblBuilder.create()
    .application(type = 32U, version = 0x10000U)
    .certificateEcdsaP256(certificate)
    .prog(flashStartAddress = 0x1000U, data = firmwareData)
    .signatureEcdsaP256(r = 0U, s = 0U)

val secureGblBytes = gblBuilder.buildToByteArray()

Modifying Existing Files

val parseResult = gblParser.parseByteArray(inputBytes)
if (parseResult is ParseResult.Success) {
    val tags = parseResult.resultList.toMutableList()

    // Find and modify bootloader tag
    val bootloaderTagIndex = tags.indexOfFirst { it is GblBootloader }
    if (bootloaderTagIndex != -1) {
        val bootloaderTag = tags[bootloaderTagIndex] as GblBootloader
        val modifiedTag = bootloaderTag.copy(bootloaderVersion = 0x20000U)
        tags[bootloaderTagIndex] = modifiedTag
    }

    // Encode modified tags
    val modifiedGblBytes = gblParser.encode(tags)
    File("modified_firmware.gbl").writeBytes(modifiedGblBytes)
}

GBL Format Overview

The GBL format is a container format designed by Silicon Labs for firmware updates. It consists of a sequence of tags, where each tag serves a specific purpose in the update process.

Basic Structure

Each GBL file is composed of multiple tags in sequence. Every tag has:

  • Tag ID (4 bytes) - Identifies the tag type
  • Length field (4 bytes) - Size of tag data
  • Data (variable length) - Tag-specific content

The file always ends with an END tag containing a CRC32 checksum for integrity verification.

File Structure Diagram

┌─────────────┬─────────────┬──────────────────┐
│  Tag ID     │ Data Length │    Tag Data      │
│  (4 bytes)  │  (4 bytes)  │   (variable)     │
│  uint32_le  │  uint32_le  │   byte array     │
└─────────────┴─────────────┴──────────────────┘

Important: All multi-byte values use Little-Endian byte order.

Supported Tag Types

Tag Type ID (Hex) Description Data Size
HEADER_V3 0x03A617EB GBL file header (version 3) Variable
BOOTLOADER 0xF50909F5 Bootloader information Variable
APPLICATION 0xF40A0AF4 Application data Variable
METADATA 0xF60808F6 File metadata Variable
PROG 0xFE0101FE Raw programming data Variable
PROG_LZ4 0xFD0505FD LZ4-compressed programming data Variable
PROG_LZMA 0xFD0707FD LZMA-compressed programming data Variable
ERASEPROG 0xFD0303FD Memory erase command 8 bytes
VERSION_DEPENDENCY 0x76A617EB Version requirements check Variable
ENCRYPTION_DATA 0xF90707F9 Encrypted payload data Variable
ENCRYPTION_INIT 0xFA0606FA Encryption initialization data Variable
SIGNATURE_ECDSA_P256 0xF70A0AF7 ECDSA P-256 signature for auth 64 bytes
CERTIFICATE_ECDSA_P256 0xF30B0BF3 ECDSA P-256 certificate Variable
SE_UPGRADE 0x5EA617EB SE upgrade information Variable
END 0xFC0404FC Final tag with CRC 4 bytes

API Reference

Core Classes

Gbl

Main parser class for reading and writing GBL files.

class Gbl {
    fun parseByteArray(byteArray: ByteArray): ParseResult
    fun encode(tags: List<Tag>): ByteArray
}

Gbl.GblBuilder

Builder class for creating GBL files with a fluent API.

class GblBuilder {
    companion object {
        fun create(): GblBuilder  // Creates container with header/end tags
        fun empty(): GblBuilder   // Creates empty container
    }
    
    // Tag building methods
    fun application(type: UInt = 32U, version: UInt = 5U, capabilities: UInt = 0U, 
                   productId: UByte = 54U, additionalData: ByteArray = ByteArray(0)): GblBuilder
    fun bootloader(bootloaderVersion: UInt, address: UInt, data: ByteArray): GblBuilder
    fun prog(flashStartAddress: UInt, data: ByteArray): GblBuilder
    fun progLz4(flashStartAddress: UInt, compressedData: ByteArray, decompressedSize: UInt): GblBuilder
    fun progLzma(flashStartAddress: UInt, compressedData: ByteArray, decompressedSize: UInt): GblBuilder
    fun seUpgrade(version: UInt, data: ByteArray): GblBuilder
    fun metadata(metaData: ByteArray): GblBuilder
    fun eraseProg(): GblBuilder
    fun versionDependency(dependencyData: ByteArray): GblBuilder
    fun certificateEcdsaP256(certificate: ApplicationCertificate): GblBuilder
    fun signatureEcdsaP256(r: UByte, s: UByte): GblBuilder
    fun encryptionData(encryptedGblData: ByteArray): GblBuilder
    fun encryptionInit(msgLen: UInt, nonce: UByte): GblBuilder
    
    // Build methods
    fun buildToByteArray(): ByteArray
    fun buildToList(): List<Tag>
    fun get(): List<Tag>
    
    // Container management
    fun hasTag(tagType: GblType): Boolean
    fun getTag(tagType: GblType): Tag?
    fun removeTag(tag: Tag): ContainerResult<Unit>
    fun clear(): ContainerResult<Unit>
    fun size(): Int
    fun isEmpty(): Boolean
    fun getTagTypes(): Set<GblType>
}

Data Classes

ApplicationData

data class ApplicationData(
    val type: UInt,
    val version: UInt,
    val capabilities: UInt,
    val productId: UByte
) {
    companion object {
        const val APP_TYPE: UInt = 32U
        const val APP_VERSION: UInt = 5U
        const val APP_CAPABILITIES: UInt = 0U
        const val APP_PRODUCT_ID: UByte = 54U
    }
}

ApplicationCertificate

data class ApplicationCertificate(
    val structVersion: UByte,
    val flags: UByte,
    val key: UByte,
    val version: UInt,
    val signature: UByte
)

Result Types

ParseResult

sealed class ParseResult {
    data class Success(val resultList: List<Tag>) : ParseResult()
    data class Fatal(val error: Any? = null) : ParseResult()
}

ContainerResult

sealed class ContainerResult<out T> {
    data class Success<T>(val data: T) : ContainerResult<T>()
    data class Error(val message: String, val code: ContainerErrorCode) : ContainerResult<Nothing>()
}

enum class ContainerErrorCode {
    CONTAINER_NOT_CREATED,
    PROTECTED_TAG_VIOLATION,
    TAG_NOT_FOUND,
    INTERNAL_ERROR
}

Container System

The library includes a sophisticated container system for managing GBL tags:

  • Automatic management of protected tags (HEADER_V3 and END)
  • Validation of tag integrity and relationships
  • Error handling with detailed error codes
  • Flexible building capabilities

Protected Tags

The container automatically manages:

  • HEADER_V3: Always first tag, created automatically
  • END: Always last tag, contains calculated CRC

You cannot manually add or remove these tags - they are managed by the container system.

Advanced Features

Tag Management

val builder = Gbl.GblBuilder.create()

// Check if tag exists
if (builder.hasTag(GblType.APPLICATION)) {
    val appTag = builder.getTag(GblType.APPLICATION)
}

// Remove specific tag
val result = builder.removeTag(someTag)
when (result) {
    is ContainerResult.Success -> println("Tag removed")
    is ContainerResult.Error -> println("Error: ${result.message}")
}

// Get all tag types
val tagTypes = builder.getTagTypes()

File Processing Flow

  1. Bootloader reads the header tag to determine file format version
  2. Tags are processed sequentially according to their type
  3. Verification occurs (signatures, CRC checksums)
  4. Flash operations are performed according to tag commands
  5. Device resets after successful update completion

Best Practices

Error Handling

Always check parse results and handle errors appropriately:

when (val result = parser.parseByteArray(data)) {
    is ParseResult.Success -> {
        // Process tags
        result.resultList.forEach { tag ->
            // Handle each tag
        }
    }
    is ParseResult.Fatal -> {
        logger.error("Failed to parse GBL: ${result.error}")
        // Handle error appropriately
    }
}

Limitations

  • Only GBL version 3 files are fully supported
  • Large files are loaded entirely into memory
  • Thread safety: Create separate parser instances for concurrent use
  • Compression: LZ4 and LZMA require additional dependencies for decompression
  • Little-Endian: All multi-byte values use little-endian byte order

License

Apache License 2.0