CYCLE counter to time pulse w/ HC-SR04

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1

Here is an example of using the PRUSS cycle counter to time a pulse.

Files at: github.org/jstampfl/Prutimer

here is the PRUSS code:

`
/ pt.p

// To get the echo pulse on pin P8 15.
// assemble: pasm -v3 -b pt.p (could be pasm_2 if you follow directions
.setcallreg r29.w0 // Going to use r31 for interrupt
.origin 0
.entrypoint T811
#define CTRL 0x22000 //Start of control registers.
T811:
mov r8,CTRL //set r8 for the lbbo
ldi r12, 0 // Local memory address for pru0 data memory
ldi r2, 0 // zero to zero the cycle counter
TB1:
qbbs TB1,r31,15 // wait here for echo line to go low

// WAIT FOR THE ECHO PULSE TB2:

qbbc TB2,r31,15 // wait here for echo line to go high - start of pulse

// START THE CYCLE COUNTER

lbbo r9,r8,0,4 // Get the control register
set r9,3 // Set the cycle counter enable
sbbo r9,r8,0,4 // Put back to the register to start

// WAIT FOR THE PULSE TO END

TB3:
qbbs TB3,r31,15 // wait here until echo line goes low.

// STOP THE CYCLE COUNTER
lbbo r9,r8,0,4 // get control register
clr r9,3 // clear counter to disable
sbbo r9,r8,0,4 // put back
ldi r10,1 // not neccessary, was going to use as signal

// GET THE CYCLE COUNT AND PUT IN PRU0 LOCAL DATA MEMORY

lbbo r11,r8,12,4 // get the CYCLE count
sbbo r10,r12,0,8 // put r10 & r11 (the unused signal & cycle count) in
// pru0 data memory
sbbo r2,r8,12,4 // Zero the cycle count

// SEND INTERRUPT SIGNAL TO LINUX SIDE

mov r31.b0,35 //Send interrupt to Linux side

lbbo r11,r12,8,4 // Check for end flag from Linux side
qbne TB1,r11,2 // go back for more
TB4:
halt

`

2

I grabbed a copy of your code from GitHub but I can’t seem to get it to compile.

I’m pretty sure it is a mis-configuration on my end.

I’m using the Debian image and have am335x-pru-package installed.

Here’s the output from GCC http://pastebin.com/VqqdaCnJ

It can’t seem to find the pruss* includes

Thanks,
Troy

3

Nevermind, I worked it out.

gcc -c -o pt.o pt.c

gcc -lpthread -lprussdrv -o pt pt.o

4

OK