Freescale Semiconductor StarCore SC140 - Manual (Page 101)

SC140 DSP Core Reference Manual 3-1
Chapter 3
Control Registers
This chapter describes the core control registers for the SC140 core.
Several bits in these registers are not used, and are marked as reserved. These bits are initialized with a
zero value and should be written with a zero value for future compatibility.
3.1 Core Control Registers
The SC140 programming model contains two 32-bit core control registers: a status register (SR) and an
exception and mode register (EMR). These registers include dedicated bits for reflecting and controlling
different operating modes of the core as well as various status flags.
3.1.1 Status Register (SR)
The SR contains 32 bits. It reflects and controls the following:
• Core working mode ( Normal or Exception)
• State of the four hardware loops and type of the currently executing loop
• Current interrupt priority level (IPL) of the core
• Overflow exceptions enabled or disabled
• Interrupts enabled or disabled
• Viterbi flags
• Scaling, rounding, and arithmetic saturation modes
• Numeric range of moved data after scaling
• Result (true or false) of a condition test
• Existence of a carry/borrow generated from the last addition/subtraction operation
• Value of last shifted bit during a DALU shift operation
When a subroutine or exception is serviced, the status register is pushed onto the stack. The following
instructions implicitly push the SR onto the stack:
• JSR/D
• BSR/D
Any exception or interrupt implicitly pushes the SR onto the stack, including exceptions that are triggered
by the following instructions:
• TRAP