Samsung SC32442B54, Руководство пользователя

Страница: 63 / 647

ARM INSTRUCTION SET SC32442B RISC MICROPROCESSOR
3-4
THE CONDITION FIELD
In ARM state, all instructions are conditionally executed according to the state of the CPSR condition codes and
the instruction's condition field. This field (bits 31:28) determines the circumstances under which an instruction is
to be executed. If the state of the C, N, Z and V flags fulfils the conditions encoded by the field, the instruction is
executed, otherwise it is ignored.
There are sixteen possible conditions, each represented by a two-character suffix that can be appended to the
instruction's mnemonic. For example, a Branch (B in assembly language) becomes BEQ for "Branch if Equal",
which means the Branch will only be taken if the Z flag is set.
In practice, fifteen different conditions may be used: these are listed in Table 3-2. The sixteenth (1111) is
reserved, and must not be used.
In the absence of a suffix, the condition field for most instructions is set to "Always" (suffix AL). This means the
instruction will always be executed regardless of the CPSR condition codes.
Table 3-2. Condition Code Summary
Code Suffix Flags Meaning
0000 EQ Z set equal
0001 NE Z clear not equal
0010 CS C set unsigned higher or same
0011 CC C clear unsigned lower
0100 MI N set negative
0101 PL N clear positive or zero
0110 VS V set overflow
0111 VC V clear no overflow
1000 HI C set and Z clear unsigned higher
1001 LS C clear or Z set unsigned lower or same
1010 GE N equals V greater or equal
1011 LT N not equal to V less than
1100 GT Z clear AND (N equals V) greater than
1101 LE Z set OR (N not equal to V) less than or equal
1110 AL (ignored) always