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PRU code

Kevin the almighty
Intellectual 780 points

Hi this assembly doesn't really look like the stuff i've seen before, actually i used an old motorola for school and it was a bit different, two registers, 8bits,  very very basic, this seems to bit more complex,

first, you can use r1->r32, there are 32 different registers? whats it mean when they add the .b0 .w0...

and in the example

#define CONST_PRU1DRAM C4

well just don't get this, sort of, nothing specifies what PRU1DRAM is i mean the location, and i know c4 has something to do with tables but don't underst what it is, is it just an adress of a table?

 

  • 0
    TI__Genius 15910 points

    Yes, each PRU has 32 different registers.  All instructions are performed on these registers.  The PRU can individually select bits, bytes, and half-words within individual registers.  Refer to the table below meanings of these suffixes.  The following link also shows illustrates this:  http://processors.wiki.ti.com/index.php/PRU_Assembly_Advanced_Topics#Register_Addressing_and_Spanning.

     

    Suffix
    		 Range of n
    		 Meaning
    .wn
    		 0 to 2
    		 16 bit field with a byte offset of
    n within the parent field
    .bn
    		 0 to 3
    8 bit field with a byte offset of n within the parent field
    .tn
    		 0 to 31
    1 bit field with a bit offset of n within the parent field

     

    The address of PRU1DRAM is stored into the 4th entry of the PRU's constant table.  See http://processors.wiki.ti.com/index.php/Programmable_Realtime_Unit#Constants_Table.  Loading and storing instructions on the PRU require that the destination/source base address be loaded into a register.  The constant table contains 32 commonly-used addresses that can be used in memory to load/store operations via special instructions (LBCO/SBCO).  So instead of first storing an address into a register and then using SBBO or LBBO to move data to or from that address, the constant table allows you to move data to or from an address in a single instruction. 

    You may also find these training slides helpful:  http://processors.wiki.ti.com/images/1/18/PRUSS_Training_Slides.pdf.

    Regards, Melissa