Register Conventions; Status Registers - Texas Instruments TMS320 DSP User Manual

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5.4.3 Register Conventions

This section describes the rules and guidelines that apply to the use of the TMS320C54xx on-chip
registers. As described above, there are several different register types. Note that any register that is not
described here must not be accessed by an algorithm; e.g., BSCR, IFR, IMR, and peripheral control and

status registers.

The table below describes all of the registers that may be accessed by an algorithm
Register
AR0, AR2-AR5
AR7
AR1, AR6
AL, AH, AG
BL, BH, BG
BK
BRC
IFR, IMR
PMST
RSA, REA
SP
ST0, ST1
T
TRN
XPC
5.4.4 Status Registers
The C54xx contains three status registers: ST0, ST1, and PMST. Each status register is further divided
into several distinct fields. Although each field is often thought of as a separate register, it is not possible
to access these fields individually. In order to set one field, it is necessary to set all fields in the same
status register. Therefore, it is necessary to treat the status registers with special care. For example, if any
field of a status register is of type Preserve, the entire register must be treated as a Preserve register.
ST0 Field Name
ARP
C
DP
OVA
OVB
TC
The ST1 register is of type Init.
ST1 Field Name
ASM
BRAF
C16
CMPT
CPL
FRCT
HM
SPRU352G – June 2005 – Revised February 2007
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Use
C compiler expression registers
C compiler frame pointer
C compiler register variables
Return value from C function, first parameter to function
C compiler expression registers
Circular-buffer size register
Block repeat counter
Interrupt flag and mask register
Processor mode register
Block repeat start and end register
Stack pointer
Status registers
Multiply and shift operand
Viterbi transition register
Extended Program Counter
Use
Auxiliary register pointer
Carry bit
Data page pointer
Overflow flag for accumulator A
Overflow flag for accumulator B
Test/Control flag
Use
Accumulator shift mode
Block repeat active bit
Dual 16-bit math bit
Compatibility mode bit
Compiler mode bit
Fractional mode bit
Hold mode bit
TMS320C54xx Rules and Guidelines
Type
Scratch (local)
Preserve (local)
Preserve (local)
Scratch (local)
Scratch (local)
Scratch (local)
Scratch (local)
Read-only (global)
Preserve
Scratch (local)
Preserve (local)
Preserve
Scratch (local)
Scratch (local)
Scratch (local)
Type
Init (local)
Scratch (local)
Scratch (local)
Scratch (local)
Scratch (local)
Scratch (local)
Type
Scratch (local)
Preserve (local)
Init (local)
Init (local)
Init (local)
Init (local)
Preserve (local)
DSP-Specific Guidelines 51