Conditional Sequencing - Analog Devices ADSP-21261 SHARC Hardware Reference Manual

• PC stack full. Bit 21 (
or not full (if 0)—not a sticky bit, cleared by a
• PC stack empty. Bit 22 (
(if 1) or not empty (if 0)—not sticky, cleared by a
Table A-5 on page A-18
To prevent a PC stack overflow, the PC stack full condition generates the
(maskable) stack overflow interrupt (
the PC stack has 29 of 30 locations filled (the almost full state). The PC
stack full interrupt occurs when at this point because the PC stack full
interrupt service routine needs that last location for its return address.
The address of the top of the PC stack is available in the
( ) register. The value of
PCSTKP
is 1 through 30 when the stack contains data, and is 31 when the stack
overflows. A write to
stack is overflowed, a write to
read from and written to.
The overflow and full flags provide diagnostic aid only. Programs should
not use these flags for runtime recovery from overflow. Note that the sta-
tus stack, loop stack overflow, and PC stack full conditions trigger a
maskable interrupt.
The empty flags can ease stack saves to memory. Programs can monitor
the empty flag when saving a stack to memory to determine when the DSP
has transferred all values.

Conditional Sequencing

The sequencer supports conditional execution with conditional logic, as
illustrated in Figure 3-6 on page
conditional (
IF
ditions are based on information from the arithmetic status registers
ADSP-2126x SHARC Processor Hardware Reference
PCFL
PCEM
lists all the bits in the
PCSTKP
takes effect after a one cycle delay. If the PC
PCSTKP
PCSTKP
3-62. This logic evaluates conditions for
) instructions and loop (
Program Sequencer
) indicates that the PC stack is full (if 1)
) indicates that the PC stack is empty
STYKx
). This interrupt occurs when
SOVFI
is zero when the PC stack is empty,
has no effect. This register can be
) terminations. The con-
DO/UNTIL
.
POP
.
PUSH
register.
stack pointer
PC
3-17