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Conventions that this manual uses are described in the following sections:


The typographical conventions are:


Highlights important notes, introduces special terminology, denotes internal cross-references, and citations.


Highlights interface elements, such as menu names. Denotes signal names. Also used for terms in descriptive lists, where appropriate.


Denotes text that you can enter at the keyboard, such as commands, file and program names, and source code.


Denotes a permitted abbreviation for a command or option. You can enter the underlined text instead of the full command or option name.

monospace italic

Denotes arguments to monospace text where the argument is to be replaced by a specific value.

monospace bold

Denotes language keywords when used outside example code.

< and >

Angle brackets enclose replaceable terms for assembler syntax where they appear in code or code fragments. They appear in normal font in running text. For example:

  • MRC p15, 0 <Rd>, <CRn>, <CRm>, <Opcode_2>

  • The Opcode_2 value selects which register is accessed.

Timing diagrams

The figure named Figure 1 Figure 1 explains the components used in timing diagrams. Variations, when they occur, have clear labels. You must not assume any timing information that is not explicit in the diagrams. Shaded bus and signal areas are undefined, and the bus or signal can assume any value within the shaded area at that time. The actual level is unimportant and does not affect normal operation.

Figure 1. Key to timing diagram conventions

Figure 1. Key to timing diagram conventions

Signal naming

When a signal is described as asserted, the level depends on whether the signal is active-HIGH or active-LOW. Asserted means HIGH for active-HIGH signals and LOW for active-LOW signals:

Prefix A

Advanced eXtensible Interface (AXI) global and address channel signals are prefixed by an upper case A.

Prefix B

AXI write response channel signals are prefixed by an upper case B.

Prefix C

AXI low-power interface signals are prefixed by an upper case C.

Prefix H

Advanced High-performance Bus (AHB) signals are prefixed by an upper case H.

Prefix n

Active-low signals are prefixed by a lowercase n except in the case of AHB or Advanced Peripheral Bus (APB) reset signals. These are named HRESETn and PRESETn respectively.

Prefix P

APB signals are prefixed by an upper case P.

Prefix R

AXI read channel signals are prefixed by an upper case R.

Prefix W

AXI write channel signals are prefixed by an upper case W.


<size in bits>’<base><number>

This is a Verilog method of abbreviating constant numbers. For example:

  • ‘h7B4 is an unsized hexadecimal value.

  • ‘o7654 is an unsized octal value.

  • 8’d9 is an eight-bit wide decimal value of 9.

  • 8’h3F is an eight-bit wide hexadecimal value of 0x3F. This is equivalent to b00111111.

  • 8’b1111 is an eight-bit wide binary value of b00001111.

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