Increasing timing errors with rosserial

[Hommus]

I'm running the following code on a SAMD21 chip (identical to the Arduino Zero) and seeing a gradual timing offset between the MCU and my host device (a Xavier NX). Any suggestions on how to debug this? Are the functions just called too fast?

#include "Arduino.h"

#include <ros.h>
#include <std_msgs/Time.h>

ros::NodeHandle nh;

std_msgs::Time time_msg;
ros::Publisher chatter_time("chatter_time", &time_msg);

void setup()
{
  nh.getHardware()->setBaud(500000);
  nh.initNode();
  nh.advertise(chatter_time);
}

void loop()
{
  time_msg.data = nh.now();
  chatter_time.publish( &time_msg );
  nh.spinOnce();
  delay(1);
}

# Terminal 1
roscore
# Terminal 2
rosrun rosserial_arduino serial_node.py _port:=/dev/versavis _baud:=500000
# Terminal 3
rostopic echo /chatter_time --offset

data: 
  secs: 0
  nsecs:   5362967
---
data: 
  secs: 0
  nsecs:   3650985
---
data: 
  secs: 0
  nsecs:   2202932
---
data: 
  secs: 0
  nsecs:    828882
---
data: 
  secs: -1
  nsecs: 999503046
---
data: 
  secs: -1
  nsecs: 998166096

...

data: 
  secs: -1
  nsecs:   5201935
---
data: 
  secs: -1
  nsecs:   3447084
---
data: 
  secs: -1
  nsecs:   2268113
---
data: 
  secs: -1
  nsecs:   1016040
---
data: 
  secs: -2
  nsecs: 999823003
---
data: 
  secs: -2
  nsecs: 998548088
---
data: 
  secs: -2
  nsecs: 996856040
---
data: 
  secs: -2
  nsecs: 995202994