1Image Terminology
2=================
3
4This page contains the current name, abbreviated name and purpose of the various
5images referred to in the Trusted Firmware project.
6
7General Notes
8-------------
9
10- Some of the names and abbreviated names have changed to accommodate new
11  requirements. The changed names are as backward compatible as possible to
12  minimize confusion. Where applicable, the previous names are indicated. Some
13  code, documentation and build artefacts may still refer to the previous names;
14  these will inevitably take time to catch up.
15
16- The main name change is to prefix each image with the processor it corresponds
17  to (for example ``AP_``, ``SCP_``, ...). In situations where there is no
18  ambiguity (for example, within AP specific code/documentation), it is
19  permitted to omit the processor prefix (for example, just BL1 instead of
20  ``AP_BL1``).
21
22- Previously, the format for 3rd level images had 2 forms; ``BL3`` was either
23  suffixed with a dash ("-") followed by a number (for example, ``BL3-1``) or a
24  subscript number, depending on whether rich text formatting was available.
25  This was confusing and often the dash gets omitted in practice. Therefore the
26  new form is to just omit the dash and not use subscript formatting.
27
28- The names no longer contain dash ("-") characters at all. In some places (for
29  example, function names) it's not possible to use this character. All dashes
30  are either removed or replaced by underscores ("_").
31
32- The abbreviation BL stands for BootLoader. This is a historical anomaly.
33  Clearly, many of these images are not BootLoaders, they are simply firmware
34  images. However, the BL abbreviation is now widely used and is retained for
35  backwards compatibility.
36
37- The image names are not case sensitive. For example, ``bl1`` is
38  interchangeable with ``BL1``, although mixed case should be avoided.
39
40Trusted Firmware Images
41-----------------------
42
43AP Boot ROM: ``AP_BL1``
44~~~~~~~~~~~~~~~~~~~~~~~
45
46Typically, this is the first code to execute on the AP and cannot be modified.
47Its primary purpose is to perform the minimum initialization necessary to load
48and authenticate an updateable AP firmware image into an executable RAM
49location, then hand-off control to that image.
50
51AP RAM Firmware: ``AP_BL2``
52~~~~~~~~~~~~~~~~~~~~~~~~~~~
53
54This is the 2nd stage AP firmware. It is currently also known as the "Trusted
55Boot Firmware". Its primary purpose is to perform any additional initialization
56required to load and authenticate all 3rd level firmware images into their
57executable RAM locations, then hand-off control to the EL3 Runtime Firmware.
58
59EL3 Runtime Firmware: ``AP_BL31``
60~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
61
62Also known as "SoC AP firmware" or "EL3 monitor firmware". Its primary purpose
63is to handle transitions between the normal and secure world.
64
65Secure-EL1 Payload (SP): ``AP_BL32``
66~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
67
68Typically this is a TEE or Trusted OS, providing runtime secure services to the
69normal world. However, it may refer to a more abstract Secure-EL1 Payload (SP).
70Note that this abbreviation should only be used in systems where there is a
71single or primary image executing at Secure-EL1. In systems where there are
72potentially multiple SPs and there is no concept of a primary SP, this
73abbreviation should be avoided; use the recommended **Other AP 3rd level
74images** abbreviation instead.
75
76AP Normal World Firmware: ``AP_BL33``
77~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
78
79For example, UEFI or uboot. Its primary purpose is to boot a normal world OS.
80
81Other AP 3rd level images: ``AP_BL3_XXX``
82~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
83
84The abbreviated names of the existing 3rd level images imply a load/execution
85ordering (for example, ``AP_BL31 -> AP_BL32 -> AP_BL33``).  Some systems may
86have additional images and/or a different load/execution ordering. The
87abbreviated names of the existing images are retained for backward compatibility
88but new 3rd level images should be suffixed with an underscore followed by text
89identifier, not a number.
90
91In systems where 3rd level images are provided by different vendors, the
92abbreviated name should identify the vendor as well as the image
93function. For example, ``AP_BL3_ARM_RAS``.
94
95SCP Boot ROM: ``SCP_BL1`` (previously ``BL0``)
96~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
97
98Typically, this is the first code to execute on the SCP and cannot be modified.
99Its primary purpose is to perform the minimum initialization necessary to load
100and authenticate an updateable SCP firmware image into an executable RAM
101location, then hand-off control to that image. This may be performed in
102conjunction with other processor firmware (for example, ``AP_BL1`` and
103``AP_BL2``).
104
105This image was previously abbreviated as ``BL0`` but in some systems, the SCP
106may directly load/authenticate its own firmware. In these systems, it doesn't
107make sense to interleave the image terminology for AP and SCP; both AP and SCP
108Boot ROMs are ``BL1`` from their own point of view.
109
110SCP RAM Firmware: ``SCP_BL2`` (previously ``BL3-0``)
111~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
112
113This is the 2nd stage SCP firmware. It is currently also known as the "SCP
114runtime firmware" but it could potentially be an intermediate firmware if the
115SCP needs to load/authenticate multiple 3rd level images in future.
116
117This image was previously abbreviated as BL3-0 but from the SCP's point of view,
118this has always been the 2nd stage firmware. The previous name is too
119AP-centric.
120
121Firmware Update (FWU) Images
122----------------------------
123
124The terminology for these images has not been widely adopted yet but they have
125to be considered in a production Trusted Board Boot solution.
126
127AP Firmware Update Boot ROM: ``AP_NS_BL1U``
128~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
129
130Typically, this is the first normal world code to execute on the AP during a
131firmware update operation, and cannot be modified. Its primary purpose is to
132load subsequent firmware update images from an external interface and communicate
133with ``AP_BL1`` to authenticate those images.
134
135During firmware update, there are (potentially) multiple transitions between the
136secure and normal world. The "level" of the BL image is relative to the world
137it's in so it makes sense to encode "NS" in the normal world images. The absence
138of "NS" implies a secure world image.
139
140AP Firmware Update Config: ``AP_BL2U``
141~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
142
143This image does the minimum necessary AP secure world configuration required to
144complete the firmware update operation. It is potentially a subset of ``AP_BL2``
145functionality.
146
147SCP Firmware Update Config: ``SCP_BL2U`` (previously ``BL2-U0``)
148~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
149
150This image does the minimum necessary SCP secure world configuration required to
151complete the firmware update operation. It is potentially a subset of
152``SCP_BL2`` functionality.
153
154AP Firmware Updater: ``AP_NS_BL2U`` (previously ``BL3-U``)
155~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
156
157This is the 2nd stage AP normal world firmware updater. Its primary purpose is
158to load a new set of firmware images from an external interface and write them
159into non-volatile storage.
160
161Other Processor Firmware Images
162-------------------------------
163
164Some systems may have additional processors to the AP and SCP. For example, a
165Management Control Processor (MCP). Images for these processors should follow
166the same terminology, with the processor abbreviation prefix, followed by
167underscore and the level of the firmware image.
168
169For example,
170
171MCP Boot ROM: ``MCP_BL1``
172~~~~~~~~~~~~~~~~~~~~~~~~~
173
174MCP RAM Firmware: ``MCP_BL2``
175~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
176