Freescale-semiconductor StarCore SC140 Manual do Utilizador descarregar pdf (Página 83)

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Address Generation Unit

SC140 DSP Core Reference Manual 2-51

2.3.6.1.1 Example of Normal Usage of the Semaphoring Mechanism

The following sequence accesses a resource controlled by a semaphore.

label : BMTSET.W #mask,(R0)

JT label

Normally, the mask enables only one bit. In this case, the memory destination pointed to by (R0) is read,

and the enabled bit is tested. The enabled bit is then set, and the memory destination is written back.

The T bit is set if the enabled bit was originally 1 (meaning that it was semaphore-occupied), or that the

write-back failed. A T bit value of TRUE indicates to the conditional jump that the attempt to obtain the

resource has failed, and that the jump should be taken. The T bit is cleared if the enabled bit was originally

zero. This means that the semaphore was not allocated. Therefore, the resource was available, and the

instruction was successful in setting the semaphore exclusively. A successful allocation writeback results.

When the destination is a register, the write is always successful.

2.3.6.2 Semaphore Hardware Implementation

During the address phase of the read and write accesses associated with the BMTSET instruction, an

output of the core is asserted. This assertion indicates that the read and the following write are part of a

read-modify-write sequence.

During the data phase of the write access, a core input provides the core with the result of the access

(de-asserted = write failed).

2.3.7 Move Instructions

The SC140 instruction set supports various types of move instructions which differ in the following

properties:

• Access width — Byte (8 bits), word (16 bits), long-word (32 bits), and two long words (64 bits)

• Data type — Signed integer, unsigned integer, fractional (with or without limiting)

• Multi-register moves — Some move operations split data between two or four registers

• Addressing mode — For example, absolute, relative to an address pointer (with various offset and

post-update options), and relative to the stack pointer

The move instructions perform data movement over the XDBA and XDBB buses (for data moves). Move

instructions do not affect the status register with the exception of the sticky scaling bit in reading a DALU

Table 2-25 lists the move instructions. The suffix just before the period in the MOVE nomenclature

indicates the following:

• None = Signed

• U = Unsigned

• S = Scaling and limiting (saturation) enabled

1 2 ... 78 79 80 81 82 83 84 85 86 87 88 ... 759 760

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