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3.17.23 TMS320C3x/C4x Options

These `-m' options are defined for TMS320C3x/C4x implementations:

Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are `c30', `c31', `c32', `c40', and `c44'. The default is `c40' to generate code for the TMS320C40.

Generates code for the big or small memory model. The small memory model assumed that all data fits into one 64K word page. At run-time the data page (DP) register must be set to point to the 64K page containing the .bss and .data program sections. The big memory model is the default and requires reloading of the DP register for every direct memory access.

Allow (disallow) allocation of general integer operands into the block count register BK.

Enable (disable) generation of code using decrement and branch, DBcond(D), instructions. This is enabled by default for the C4x. To be on the safe side, this is disabled for the C3x, since the maximum iteration count on the C3x is 2^23 + 1 (but who iterates loops more than 2^23 times on the C3x?). Note that GCC will try to reverse a loop so that it can utilise the decrement and branch instruction, but will give up if there is more than one memory reference in the loop. Thus a loop where the loop counter is decremented can generate slightly more efficient code, in cases where the RPTB instruction cannot be utilised.

Force the DP register to be saved on entry to an interrupt service routine (ISR), reloaded to point to the data section, and restored on exit from the ISR. This should not be required unless someone has violated the small memory model by modifying the DP register, say within an object library.

For the C3x use the 24-bit MPYI instruction for integer multiplies instead of a library call to guarantee 32-bit results. Note that if one of the operands is a constant, then the multiplication will be performed using shifts and adds. If the `-mmpyi' option is not specified for the C3x, then squaring operations are performed inline instead of a library call.

The C3x/C4x FIX instruction to convert a floating point value to an integer value chooses the nearest integer less than or equal to the floating point value rather than to the nearest integer. Thus if the floating point number is negative, the result will be incorrectly truncated an additional code is necessary to detect and correct this case. This option can be used to disable generation of the additional code required to correct the result.

Enable (disable) generation of repeat block sequences using the RPTB instruction for zero overhead looping. The RPTB construct is only used for innermost loops that do not call functions or jump across the loop boundaries. There is no advantage having nested RPTB loops due to the overhead required to save and restore the RC, RS, and RE registers. This is enabled by default with `-O2'.

Enable (disable) the use of the single instruction repeat instruction RPTS. If a repeat block contains a single instruction, and the loop count can be guaranteed to be less than the value count, GCC will emit a RPTS instruction instead of a RPTB. If no value is specified, then a RPTS will be emitted even if the loop count cannot be determined at compile time. Note that the repeated instruction following RPTS does not have to be reloaded from memory each iteration, thus freeing up the CPU buses for operands. However, since interrupts are blocked by this instruction, it is disabled by default.

The maximum iteration count when using RPTS and RPTB (and DB on the C40) is 2^31 + 1 since these instructions test if the iteration count is negative to terminate the loop. If the iteration count is unsigned there is a possibility than the 2^31 + 1 maximum iteration count may be exceeded. This switch allows an unsigned iteration count.

Try to emit an assembler syntax that the TI assembler (asm30) is happy with. This also enforces compatibility with the API employed by the TI C3x C compiler. For example, long doubles are passed as structures rather than in floating point registers.

Generate code that uses registers (stack) for passing arguments to functions. By default, arguments are passed in registers where possible rather than by pushing arguments on to the stack.

Allow the generation of parallel instructions. This is enabled by default with `-O2'.

Allow the generation of MPY||ADD and MPY||SUB parallel instructions, provided `-mparallel-insns' is also specified. These instructions have tight register constraints which can pessimize the code generation of large functions.

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