Fastest IO toggle

I tried but I think its triggering so fast that it never comes fully on. Readings are very low and distorted. Probably need to add a delay.

var test = E.asm("void()",
                 "ldr  r2,gpiob_addr",
                 "movw  r3,#4",
                 "loopStart:",
                 "str  r3,[r2,#0]",
                 "str  r3,[r2,#4]",
                 "b  loopStart",
                 "bx  lr",
                 "nop",
                 "gpiob_addr:",
                 ".word  0x40020418"
                 );