The compiler extends the C/C++ language by adding the __cregister keyword to allow high level language access to control registers.
When you use the __cregister keyword on an object, the compiler compares the name of the object to a list of standard control registers (see Table 7-4). If the name matches, the compiler generates the code to reference the control register. If the name does not match, the compiler issues an error.
| Register | Description |
|---|---|
| AMR | Addressing mode register |
| CSR | Control status register |
| DNUM | DSP core number register |
| ECR | Exception clear register |
| EFR | Exception flag register |
| GFPGFR | Galois field multiply control register |
| GPLYA | GMPY A-side polynomial register |
| GPLYB | GMPY B-side polynomial register |
| ICR | Interrupt clear register |
| IER | Interrupt enable register |
| IERR | Internal exception report register |
| IFR | Interrupt flag register. (IFR is read only.) |
| ILC | Inner loop count register |
| IRP | Interrupt return pointer register |
| ISR | Interrupt set register |
| ISTP | Interrupt service table pointer register |
| ITSR | Interrupt task state register |
| NRP | Nonmaskable interrupt return pointer register |
| NTSR | NMI/exception task state register |
| PCE1 | Program counter, E1 phase |
| REP | Restricted entry point address register |
| RILC | Reload inner loop count register |
| SSR | Saturation status register |
| TSCH | Time-stamp counter (high 32) register |
| TSCL | Time-stamp counter (low 32) register |
| TSR | Task state register |
The additional control registers listed in Table 7-5 are used for floating-point operations on C6740 and C6600 devices:
| Register | Description |
|---|---|
| FADCR | Floating-point adder configuration register |
| FAUCR | Floating-point auxiliary configuration register |
| FMCR | Floating-point multiplier configuration register |
The __cregister keyword can be used only in file scope. The __cregister keyword is not allowed on any declaration within the boundaries of a function. It can only be used on objects of type integer or pointer. The __cregister keyword is not allowed on objects of any floating-point type or on any structure or union objects.
The __cregister keyword does not imply that the object is volatile. If the control register being referenced is volatile (that is, can be modified by some external control), then the object must be declared with the volatile keyword also.
To use the control registers in Table 7-4, you must declare each register as follows. The c6x.h include file defines all the control registers through this syntax:
| extern __cregister volatile unsigned intregister; |
Once you have declared the register, you can use the register name directly. See the TMS320C64x/C64x+ DSP CPU and Instruction Set Reference Guide (SPRU732), the TMS320C66x DSP CPU and Instruction Set Reference Guide (SPRUGH7), or the TMS320C674x DSP CPU and Instruction Set Reference Guide (SPRUFE8) for detailed information on the control registers.
See Example 1 for an example that declares and uses control registers.