Freescale Semiconductor StarCore SC140 - Manual (Page 82)

2-50 SC140 DSP Core Reference Manual
Address Generation Unit
Table 2-24 lists the arithmetic instructions that are executed in the BMU.
2.3.6.1 Bit Mask Test and Set (Semaphore Support) Instruction
The bit mask test and set instruction (BMTSET) provides support for hardware semaphores. A semaphore
is a signal which can be set to indicate whether a program resource can be accessed or not. The destination
of this instruction can be a register or a memory location in either internal or external memory. If the
semaphore indicates that the resource is available, the T bit has the value 0. If the semaphore indicates that
the resource is not available (T = 1), a jump can be made to skip the resource code.
This instruction performs the following tasks:
1. Reads the destination register, tests the data, and sets the T bit, if every bit that has the value
1 in the mask is 1 in the destination.
2. Writes back to the destination a word with ones for the masked bits, and the original
destination bits for the unmasked bits.
3. Sets the T bit if the set (write) failed.
Normally, the BMTSET consists of three indivisible operations: read, update the T bit, and
write. A set (write) failed condition occurs if the destination failed to be written indivisibly
from the previous read operation of that BMTSET instruction. The memory subsystem
signals the core of a write failure if a memory access that is initiated by another master
source intervenes between the read and the write accesses of the BMTSET operation. As a
result of the non-exclusive write indication, the T bit is set, signalling that the resource may
not be available, thereby avoiding a hazard condition.
Table 2-24. AGU Bit Mask Instructions (BMU)
Instruction Description
AND.W Logical AND on a 16-bit operand
BMCHG Bit mask change
Inverts every bit in the destination (register or memory) that has the value 1 in the mask.
BMCLR Bit mask clear
Clears every bit in the destination (register or memory) that has the value 1 in the mask.
BMSET Bit mask set
Sets every bit position in the destination (register or memory) that has the value 1 in the mask.
BMTSET Bit mask test (if set) and set
Sets the T bit if every bit that has the value 1 in the mask is 1 in the destination (register or
memory). Sets (writes) every bit in the destination (register or memory) that has the value 1 in
the mask, and sets the T-bit if the set (write) failed. See
Section 2.3.6.1, “Bit Mask Test and Set
(Semaphore Support) Instruction.”
BMTSTC Bit mask test if clear
Sets the T-bit, if every bit position that has the value 1 in the mask is 0 in an operand.
BMTSTS Bit mask test if set
Sets the T bit if every bit position that has the value 1 in the mask is 1 in an operand.
EOR.W Logical exclusive OR on a 16-bit operand
NOT.W Binary inversion of a 16-bit operand
OR.W Logical OR on a 16-bit operand