esp-idf/components/esp32/test/test_fastbus_asm.S

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ArmAsm
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/*
This little bit of code is executed in-place by one CPU, but copied to a different memory region
by the other CPU. Make sure it stays position-independent.
*/
.text
.align 4
.global test_fastbus_cp
.type test_fastbus_cp,@function
//Args:
//a2 - fifo addr
//a3 - buf addr
//a4 - len
//a5 - ptr to int to use
test_fastbus_cp:
entry a1,64
back:
beqi a4, 0, out //check if loop done
s32i a4, a5, 0 //store value, for shits and/or giggles
memw //make sure write happens
l32i a4, a5, 0 //load value again, to thwart any prediction in the pipeline
bbsi a4, 0, pred //Random jump to check predictive reads. Both branches should do the same.
l32i a6, a2, 0 //read from fifo 1
j predout
pred:
l32i a6, a2, 0 //read from fifo 2
predout:
s8i a6, a3, 0 //store result
addi a3, a3, 1 //inc ptr
addi a4, a4, -1 //next
j back //loop again
out:
retw //and we are done