1、简介

Xilinx FPGA、SOC器件和自适应计算加速平台（ACAPs）通常由多个硬件和软件二进制文件组成，用于启动这些设备后按照预期设计进行工作。这些二进制文件可以包括FPGA比特流、固件镜像、bootloader引导程序、操作系统和用户选择的应用程序，它们可以以非安全和安全的方式进行加载。

Bootgen是一个Xilinx工具，用于整合二进制文件并且生成设备引导镜像文件。同时Bootgen在给Xilinx设备创建boot images时，定义了输入的多种特征、属性和参数。

Bootgen同时提供了GUI接口和命令行选项。集成到Vitis中的GUI用于生成基本的boot images，除此之外的多数Bootgen选项都是命令行驱动的。驱动Bootgen的是一个boot image format（BIF）配置文件，后缀.bif。

2、Boot Image结构

2.1 说明

创建一个boot image包含如下两步：

（1）创建一个BIF文件；

（2）运行Bootgen可执行文件来创建一个boot image。

Xilinx不同系列的boot image格式是不同的，这里我们只学习记录下Versal ACAP的boot image，下图是Versal ACAP boot image的组件，也被称为Programmable Device Image（PDI）。

2.2 PMC

Versal ACAP中的平台管理控制器主要用于boot和配置。我们重点关注的是两个PMC MicroBlaze处理器（ROM code unit（RCU） / platform processing unit（PPU））处理的boot image。

（1）RCU

ROM code unit包含了一个三重冗余MicroBlaze处理器和一个ROM，该ROM中包含了BootROM可执行文件。BootROM可执行文件不能被改变。RCU中的MicroBlaze用于验证和运行BootROM可执行文件。RCU还负责启动后的安全监控，以及物理防克隆功能（physical unclonable function，PUF）管理

（2）PPU

Platform processing unit也包含了一个三重冗余MicroBlaze处理器，以及一个专用的384KB大小的PPU RAM。这个MicroBlaze用于运行平台加载和管理器（platform loader and manager）。

在Versal ACAP中，自适应引擎（PL）由rCDO和rNPI文件组成。rCDO文件主要包含CFrame数据以及PL和NoC电源域初始化命令。rNPI文件包含与NPI块相关的配置数据。NPI区块包括NoC元素：NMU、NSU、NPS、NCRB；DDR、XPHY、XPIO、GTY、MMCM等。

2.3 Versal ACAP Boot Header

在boot image的顶部就是Boot Header：

PMC的BootROM会使用这里的Boot Header。基于Boot Header里面的属性信息，PMC BootROM可以验证平台加载和管理器（PLM），并将PLM加载进PPU的RAM中。

Boot Header的前16字节用于检测SelectMAP总线。PMC的BootROM和PLM会忽略这些数据，因此Bootgen在进行checksum/SHA/RSA/加密等操作时不会包含这些数据。前16字节有以下3种情况：

X8: [LSB] 00 00 00 DD 11 22 33 44 55 66 77 88 99 AA BB CC [MSB]

X16: [LSB] 00 00 DD 00 22 11 44 33 66 55 88 77 AA 99 CC BB [MSB]

X32: [LSB] DD 00 00 00 44 33 22 11 88 77 66 55 CC BB AA 99 [MSB]

以实际的PDI文件为例：

默认的SelectMAP位宽就是X32。

Boot Header具体格式如下：

Offset (Hex)	Size (Bytes)	Description	Details
0x00	16	SelectMAP bus width	Used to determine if the SelectMAP bus width is x8, x16, or x32
0x10	4	QSPI bus width	QSPI bus width description. This is required to identify the QSPI flash in single/dual stacked or dual parallel mode. 0xAA995566 in the little endian format.
0x14	4	Image identification	Boot image identification string. Contains 4 bytes X, N, L, X in byte order, which is 0x584c4e58 in the little endian format.
0x18	4	Encryption key source	This field is used to identify the AES key source: 0x00000000 0x00000000 - Unencrypted 0xA5C3C5A3 - eFUSE red key 0xA5C3C5A5 - eFUSE black key 0x3A5C3C5A - BBRAM red key 0x3A5C3C59 - BBRAM black key 0xA35C7C53 - Boot Header black key
0x1C	4	PLM source offset	PLM source start address in PDI
0x20	4	PMC data load address	PMC CDO address to load
0x24	4	PMC data length	PMC CDO length
0x28	4	Total PMC data length	PMC CDO length including authentication and encryption overhead
0x2C	4	PLM length	PLM original image size
0x30	4	Total PLM length	PLM image size including the authentication and encryption overhead
0x34	4	Boot header attributes	Boot Header Attributes
0x38	32	Black key	256-bit key, only valid when encryption status is set to black key in boot header
0x58	12	Black IV	Initialization vector used when decrypting the black key
0x64	12	Secure header IV	Secure header initialization vector
0x70	4	PUF shutter value	Length of the time the PUF samples before it closes the shutter Note: This shutter value must match the shutter value that was used during PUF registration.
0x74	12	Secure Header IV for PMC Data	The IV used to decrypt secure header of PMC data.
0x80	68	Reserved	Populate with zeroes.
0xC4	4	Meta Header Offset	Offset to the start of meta header
0xC8-0x124	96	Reserved
0x128	2048	Register init	Stores register write pairs for system register initialization
0x928	1544	PUF helper data	PUF helper data
0xF30	4	Checksum	Header checksum
0xF34	76	SHA3 padding	SHA3 standard padding

2.4 Boot Header Attributes

Field Name	Bit Offset	Width	Default Value	Description
Reserved	[31:18]	14	0x0	Reserved for future use, Must be 0
PUF Mode	[17:16]	2	0x0	0x3 - PUF 4K mode. 0x0 - PUF 12K mode.
Boot Header Authentication	[15:14]	2	0x0	0x3 - Authentication of the boot image is done, excluding verification of PPK hash and SPK ID. All others - Authentication will be decided based on eFUSE RSA/ECDSA bits.
Reserved	[13:12]	2	0x0	Reserved for future use, Must be 0
DPA counter measure	[11:10]	2	0x0	0x3 - Enabled All others disabled. (eFUSE over rides this)
Checksum selection	[9:8]	2	0x0	0x0, 0x1, 0x2 - Reserved 0x3 - SHA3 is used as hash function to do Checksum.
PUF HD	[7:6]	2	0x0	0x3 - PUF HD is part of boot header All other - PUF HD is in eFUSE.
Reserved	[5:0]	6	0x0	Reserved

2.5 Versal ACAP Image Header Table

要找到Image Header Table，需要先在Boot Header中找到0xC4 Meta Header Offset：

从实际的PDI 0xc4地址开始的4字节的值为0x00 0x04 0x9B 0xB0，那么Meta Header offset为0x0004_9BB0

Image Header表内容如下：

Offset	Name	Description
0x0	Version	0x00040000(v4.0) : 1. Added AAD support for IHT. 2. Hash is included into the 32k secure chunk. 0x00030000(v3.0): updated secure chunk size to 32 KB from 64 KB 0x00020000(v2.00): IHT, PHT sizes doubled
0x4	Total Number of Images	Total number of images in the PDI
0x8	Image header offset	Address to start of first image header
0xC	Total Number of Partitions	Total number of partitions in the PDI
0x10	Partition Header Offset	Offset to the start of partitions headers
0x14	Secondary boot device address	Indicates the address where secondary image is present. This is only valid if secondary boot device is present in attributes
0x1C	Image Header Table Attributes	Refer to Table 22: Versal ACAP Image Header Table Attributes
0x20	PDI ID	Used to identify a PDI
0x24	Parent ID	ID of initial boot PDI. For boot PDI, it will be same as PDI ID
0x28	Identification string	Full PDI if present with boot header –“FPDI” Partial/Sub-system PDI – “PPDI”
0x2C	Headers size	0-7: Image header table size in words 8-15: Image header size in words 16-23: Partition header size in words 24-31: Reserved
0x30	Total meta header length	Including authentication and encryption overhead (excluding IHT and including AC)
0x34 -0x3C	IV for encryption of meta header	IV for decrypting SH of header table
0x40	Encryption status	Encryption key source, only key source used for PLM is valid for meta header. 0x00000000 - Unencrypted 0xA5C3C5A3 - eFuse red key 0xA5C3C5A5 - eFUSE black key 0x3A5C3C5A - BBRAM red key 0x3A5C3C59 - BBRAM black key 0xA35C7C53 - Boot Header black key
0x48	Meta Header AC Offset (Word)	Word Offset to Meta Header Authentication Certificate
0x4c	Meta Header Black/IV	IV that is used to encrypt the Black key used to encrypt the Meta Header.
0x44 - 0x78	Reserved	0x0
0x7C	Checksum	A sum of all the previous words in the image header table

Image Header Table Attributes表如下：

Bit Field	Name	Description
31:14	Reserved	0
14	PUF Helper Data Location	Location of the PUF Helper Data efuse/BH
12	dpacm enable	DPA Counter Measure enable or not
11:6	Secondary boot device	Indicates the device on which rest of the data is present in. 0 - Same boot device (default) 1 - QSPI32 2 - QSPI24 3 - NAND 4 - SD0 5 - SD1 6 - SDLS 7 - MMC 8 - USB 9 - ETHERNET 10 - PCIe 11 - SATA 12 - OSPI 13 - SMAP 14 - SBI 15 - SD0RAW 16 - SD1RAW 17 - SDLSRAW 18 - MMCRAW 19 - MMC0 20 - MMC0RAW All others are reserved Note: These options are supported for various devices in Bootgen. For the exact list of secondary boot devices supported by any device, refer to its corresponding Systems Software Developers Guide (SSDG).
5:0		Reserved

从Image Header Table的地址0x1c查到Image Header Table Attributes的4字节内容为0x0000_0000：

2.6 Versal ACAP Image Header

要找到Image Header，需要先在Image Header Table中找到地址0x8 Image header offset的4字节内容：

4字节内容为0x0001_270c，即Image Header是从地址0x0001_270c开始：

Image Header内容如下：

Offset	Name	Description
0x0	First Partition Header	Word offset to first partition header
0x4	Number of Partitions	Number of partitions present for this image
0x8	Revoke ID	Revoke ID for Meta Header
0xC	Image Attributes	See Image Attributes table
0x10-0x1C	Image Name	ASCII name of the image. Max of 16 characters. Fill with Zeros when padding is required.
0x20	Image/Node ID	Defines the resource node the image is initializing
0x24	Unique ID	Defines the affinity/compatibility identifier when required for a given device resource
0x28	Parent Unique ID	Defines the required parent resource UID for the configuration content of the image, if required
0x2c	Function ID	Identifier used to capture the unique function of the image configuration data
0x30	DDR Low Address for Image Copy	The DDR lower 32-bit address where the image should be copied when memcpy is enabled in BIF
0x34	DDR High Address for Image Copy	The DDR higher 32-bit address where image should be copied when memcpy is enabled in BIF
0x38	Reserved
0x3C	Checksum	A sum of all the previous words.

Image Header Attibutes内容如下：

Bit Field	Name	Description
31:9	Reserved	0
8	Delay Hand off	0 – Handoff the image now (default) 1 – Handoff the image later
7	Delay load	0 – Load the image now (default) 1 – Load the image later
6	Copy to memory	0 – No copy to memory (Default) 1 – Image to be copied to memory
5:3	Image Owner	0 - PLM (default) 1 - Non-PLM 2-7 – Reserved
2:0	Reserved	0