AXI timer capture mode

I am trying to develop a simple counter triggered by some events. The design is the following:

Where the custom IP timer_hls has the following code:

#include "ap_axi_sdata.h"
#include "hls_stream.h"
#include <ap_fixed.h>

typedef ap_fixed<32, 1> ap_fixed_input_type;
typedef ap_fixed<32, 1> ap_fixed_output_type;

typedef hls::axis<ap_fixed_input_type,0,0,0> pkt_t;

typedef hls::axis<ap_fixed_output_type,0,0,0> pkt_t_out;

void timer_hls(
		hls::stream< pkt_t > &din,
		hls::stream< pkt_t_out > &dout,
		ap_uint<1> & interrupt) {
	#pragma HLS INTERFACE ap_ctrl_none port=return
	#pragma HLS INTERFACE axis port=din
	#pragma HLS INTERFACE axis port=dout
	#pragma HLS INTERFACE ap_none register port=interrupt

	pkt_t pkt;
	pkt_t_out pkt_out;
	static int counter=0;

	ap_fixed_input_type input_ap_fixed = 0;
	ap_fixed_output_type output_ap_fixed = 0;;
	input_ap_fixed =;

	pkt_out.last = pkt.last;
	pkt_out.keep = pkt.keep;
	pkt_out.strb = pkt.strb; = input_ap_fixed;


	counter ++;

		counter = 0;
		interrupt = 1;


These IP will count the input packets until a given number, then they generate an interrupt which is captured by the Vivado AXI timer IP. I will use these 2 IP + Vivado Timer to exactly measure the latency/computation time of another IP, which will be inserted between the two timer_hls IPs.

In my PYNQ code I set up everything and the design works fine: the input is correctly handled with a DMA, sent into the two timer_hls IPs and then saved back into memory.

However the Vivado Timer IP never gets interrupted via capture pins and I am not able to save the clock counter.

The Vivado AXI timer IP seems to work fine, if I write:

timer = overlay.axi_timer_0

time_0 =

time_1 =

I can see that it is counting correctly. However if i write:

timer.write(0x00, 1097) #setting the registers of AXI timer

And I read back:


I get 0b10011001001 → the interrupt of the counter (bit number 8) is always zero, this means that my capture pin never captures anything.

What am I missing?

Hi @mattiasu96,

From your description it seems that everything is setup properly.
Have you verified that the interrupt pin is asserted?


In the end it was a problem with the “format” of my interrupt pin, it was interpreted as an ap_fixed and not as an interrupt