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INSTRUCTION SET
S3C2501X
3-12
3.5.2 SHIFTS
When the second operand is specified to be a shifted register, the operation of the barrel shifter is controlled by
the shift field in the instruction. This field indicates the type of shift to be performed (logical left or right, arithmetic
right or rotate right). The amount by which the register should be shifted may be contained in an immediate field
in the instruction, or in the bottom byte of another register (other than R15). The encoding for the different shift
types is shown in Figure 3-5.
[6:5] Shift Type
00 = logical left
01 = logical right
10 = arithmetic right 11 = rotate right
[11:7] Shift Amount
5 bit unsigned integer
[6:5] Shift Type
00 = logical left
01 = logical right
10 = arithmetic right 11 = rotate right
[11:8] Shift Register
Shift amount specified in bottom-byte of Rs
4
5
6
7
11
1
4
5
6
7
11
8
0
RS
Figure 3-5. ARM Shift Operations
3.5.2.1 Instruction Specified Shift Amount
When the shift amount is specified in the instruction, it is contained in a 5 bit field which may take any value from
0 to 31. A logical shift left (LSL) takes the contents of Rm and moves each bit by the specified amount to a more
significant position. The least significant bits of the result are filled with zeros, and the high bits of Rm which do
not map into the result are discarded, except that the least significant discarded bit becomes the shifter carry
output which may be latched into the C bit of the CPSR when the ALU operation is in the logical class (see
above). For example, the effect of LSL #5 is shown in Figure 3-6.
31
27 26
Contents of Rm
Value of Operand 2
carry out
0
0
0
0
0
0
Figure 3-6. Logical Shift Left
NOTE
LSL #0 is a special case, where the shifter carry out is the old value of the CPSR C flag. The contents of
Rm are used directly as the second operand. A logical shift right (LSR) is similar, but the contents of Rm
are moved to less significant positions in the result. LSR #5 has the effect shown in Figure 3-7
.
Содержание S3C2501X
Страница 1: ...S3C2501X 32 BIT RISC MICROPROCESSOR USER S MANUAL Revision 1 查询S3C2501X供应商 捷多邦 专业PCB打样工厂 24小时加急出货 ...
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Страница 275: ...MEMORY CONTROLLER S3C2501X 5 60 NOTES ...
Страница 289: ...I2C CONTROLLER S3C2501X 6 14 NOTES ...
Страница 373: ...GDMA CONTROLLER S3C2501X 9 24 NOTES ...
Страница 435: ...I O PORTS S3C2501X 12 12 NOTES ...
Страница 463: ...ELECTRICAL DATA S3C2501X 15 6 NOTES ...