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21264/EV68A Hardware Reference Manual
• Sign extension
SEXT(x) means x is sign-extended to the required size.
Addresses
Unless otherwise noted, all addresses and offsets are hexadecimal.
Aligned and Unaligned
The terms aligned and naturally aligned are interchangeable and refer to data objects
that are powers of two in size. An aligned datum of size 2n is stored in memory at a
byte address that is a multiple of 2n; that is, one that has n low-order zeros. For ex-
ample, an aligned 64-byte stack frame has a memory address that is a multiple of 64.
A datum of size 2n is unaligned if it is stored in a byte address that is not a multiple of
2n.
Bit Notation
Multiple-bit fields can include contiguous and noncontiguous bits contained in square
brackets ([]). Multiple contiguous bits are indicated by a pair of numbers separated by a
colon [:]. For example, [9:7,5,2:0] specifies bits 9,8,7,5,2,1, and 0. Similarly, single bits
are frequently indicated with square brackets. For example, [27] specifies bit 27. See
also Field Notation.
Caution
Cautions indicate potential damage to equipment or loss of data.
RW Read/Write
Bits and fields can be read and written.
RW,n Read/Write, and takes the value n at power-on reset.
Bits and fields can be read and written.
W1C Write One to Clear
If read operations are allowed to the register, then the value may be read by
software. If it is a write-only register, then a read operation by software
returns an UNPREDICTABLE result. Software write operations of a 1 cause
the bit to be cleared by hardware. Software write operations of a 0 do not
modify the state of the bit.
W1S Write One to Set
If read operations are allowed to the register, then the value may be read by
software. If it is a write-only register, then a read operation by software
returns an UNPREDICTABLE result. Software write operations of a 1 cause
the bit to be set by hardware. Software write operations of a 0 do not modify
the state of the bit.
WO Write Only
Bits and fields can be written but not read.
WO,n Write Only, and takes the value n at power-on reset.
Bits and fields can be written but not read.
Abbreviation Meaning