• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 97 subscribers
  • Views 495 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

mmap() Assembler

Jeffrey Prinzie
Prodigy 20 points
Other Parts Discussed in Thread: TMS320C5515

Dear,

I am using a TMS320C5515 DSP processor.

When running through the examples, i noticed the usage of mmap().
What exactly is the purpose of this?

for example:

mov #10,BSA45 does not use mmap

where mov #10,mmap(ST0_55) does use the mmap.

In the first case, using mmap or not does not matter, but in the second one a warning occures when not using mmap.
I can see in the assembler guide that the mov Smem,BSA45 is included were ST0_55 is not.

I do understand that mmap forces the XDP and SP to 0 so dma is always reffered to address 0 but I dont understand why ST0_55 needs mmap and BSA45 does not need it. Both are registers of the CPU. And why ST0_55 is not included in the assembler list (loading immediate values to CPU registers).

Thanks

  • 0
    TI__Guru* 84285 points

    The mmap modifier means "memory-mapped register."  To save opcode space, not every possible combination of operands is supported.  That is, not every register operand is really a register operand; sometimes you have to use mmap addressing, which is actually a memory read/write.

    The instruction MOV #10, BSA45 actually uses an opcode dedicated to BSA45 and does not use memory.

    The instruction MOV #10, mmap(ST0_55) is actually of the form MOV #n, Smem, and writes to memory.

  • 0 in reply to Archaeologist
    Prodigy 20 points

    ok,

    so the mov #1,BSA45 does not use the address of the register to access it? just a logical number in the opcode that de decoder knows?

    and mov #1,mmap(ST0_55)   works the same as e.g.  mov #10,*(#0x004C) ?

    In fact, mov #1,BSA45  does not have the same execution flow as mov #1,mmap(BSA45)? (first = "access using number as operand", second = "normal addressed access using address as operand")

    is that correct?

    Thank you!!!!