wordcopy_burst.picoasm

.include "picoasm_hal.h"

#define hir_base x1
#define burst_base x2
#define msb_set x3
#define mask_4_lsb x4
#define src x5
#define dst x6
#define num_elems x7
#define burst_end x8
#define single_end x9
#define stat_busy x10
#define tmp x11

/*Word Copy using burst mode*/

    .text
    .balign 4
    .globl _start
    /*Status register values*/
    .equ STAT_START, 1
    .equ STAT_BUSY, 3
    .equ STAT_DONE, 0

_start:
    /*Set up constants.*/
    li hir_base, HIR_REGS_BASE_ADDR
    li burst_base, BURST_REGS_BASE_ADDR
    sw zero, BURST_OFFSET(burst_base)    /*no src-to-dest alignment offset.*/
    li msb_set, 0x80000000
    li mask_4_lsb, 0xfffffff0            /*mask to clear 4 lsbs*/
    li stat_busy, STAT_BUSY
wait_start:
    lw tmp, HIR3(hir_base)               /*HIR3: ctrl-status*/
    beqz tmp, wait_start
    sw stat_busy, HIR3(hir_base)         /*set status to 'Busy'*/

    lw src, HIR0(hir_base)               /*HIR0: src pointer*/
    lw dst, HIR1(hir_base)               /*HIR1: dst pointer*/
    lw num_elems, HIR2(hir_base)         /*HIR2: num words*/
    slli num_elems, num_elems, 2         /*Multiple by 4 to convert to byte address offset.*/
    add single_end, num_elems, src       /*Turn into single end pointer.*/
    and burst_end, num_elems, mask_4_lsb /*Nearest lower burst boundary*/
    add burst_end, burst_end, src        /*Turn into burst end pointer.*/
    
    bgeu src, burst_end, single_loop_start
    or src, src, msb_set                 /*Set msb to engage burst mode*/
    or dst, dst, msb_set                 /*Set msb to engage burst mode*/
    or burst_end, burst_end, msb_set     /*Set msb to engage burst mode*/

burst_loop:
    /*Copy 4-word burst by 4-word burst*/
    lw tmp, 0(src)
    addi src, src, 16
    sw tmp, 0(dst)
    addi dst, dst, 16
    bltu src, burst_end, burst_loop

    xor src, src, msb_set  /*Clear msb again to turn off burst mode.*/
    xor dst, dst, msb_set  /*Clear msb again to turn off burst mode.*/

    /*Copy remaining words word-by-word until we get to the end pointer.*/
single_loop_start:
    bgeu src, single_end, end

single_loop:
    lw tmp, 0(src)
    addi src, src, 4
    sw tmp, 0(dst)
    addi dst, dst, 4
    bltu src, single_end, single_loop

end:
    sw zero, BURST4(burst_base) /*Do one more write to a burst register to ensure last burst transaction completed.*/
    sw zero, HIR3(hir_base) /*set to 'Done'*/
    j wait_start