Description
Hardware:
Board: ESP32 Dev Module
Core Installation version: 1.0.4, 1.0.5
IDE name: Arduino IDE
Flash Frequency: n.a.
PSRAM enabled: n.a.
Upload Speed: n.a.
Computer OS: Debian 10
Description:
Sucsessive calls to readBytes() trigger a timeout in de example below. Is there a way to avoid this, or is this perhaps a bug in one of the core libraries?
When calling readBytes() twice in succession, the second call takes a lot longer than the first one. This behaviour seems to be occurring only when using the WiFi interface, both the Bluetooth and the Serial interface are not affected. This behaviour seems to be specific to this setup, other WiFi modules are not affected.
Sketch:
#include <WiFi.h>
#include "config.h" // SSID, PASS and PORT.
/* Timing measurement functions. */
#define SLOTS 100
unsigned long _last[SLOTS];
size_t _index = 0;
void _set(void) {
_last[_index] = millis();
_index++;
}
void _delta(char* label) {
_index--;
char buf[80];
sprintf(buf, "%04i %s", millis() - _last[_index], label);
Serial.println(buf);
}
/* End timing measurement functions. */
WiFiServer server(PORT);
void setup(void) {
Serial.begin(9600);
WiFi.begin(SSID, PASS);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
}
server.begin();
}
void loop(void) {
WiFiClient client = server.available();
if (client) {
while (client.connected()) {
if (client.available()) {
uint8_t c;
_set();
client.readBytes(&c, sizeof(uint8_t));
_delta("read 1");
/* Offending snippet. */
_set();
client.readBytes(&c, sizeof(uint8_t));
_delta("read 2");
/* End offending snippet. */
_set();
client.write(c);
_delta("write");
}
}
client.stop();
}
}Host code:
from serial import serial_for_url
from time import time
# Timing measurement functions.
_last = []
def _ms():
return int(round(time() * 1000))
def _set():
_last.append(_ms())
def _delta(label):
print('{:04d} {}'.format(_ms() - _last.pop(-1), label))
# End timing measurement functions.
def test_raw(calls):
connection = serial_for_url("socket://192.168.21.53:1025")
_set()
for _ in range(calls):
_set()
connection.write(b'\x00')
_delta("write 1")
# Offending snippet.
_set()
connection.write(b'\x00')
_delta("write 2")
# End offending snippet.
_set()
connection.read()
_delta("read")
_delta("total")
test_raw(3);Debug Messages:
When we run the code as is, we see the following output:
Arduino | Host
------------+-------------
0000 read 1 | 0000 write 1
0244 read 2 | 0000 write 2
0001 write | 0254 read
0000 read 1 | 0001 write 1
0248 read 2 | 0000 write 2
0002 write | 0252 read
0000 read 1 | 0001 write 1
0242 read 2 | 0000 write 2
0001 write | 0249 read
| 0757 total
Notice that read 2 takes a long time as seen from the perspective of the Arduino, while read takes a long time as seen from the perspective of the host.
When the offending snippets are commented out, we see the following output:
Arduino | Host
------------+-------------
0000 read 1 | 0001 write 1
0001 write | 0006 read
0000 read 1 | 0000 write 1
0001 write | 0005 read
0000 read 1 | 0000 write 1
0001 write | 0004 read
| 0016 total
Which is expected behaviour.
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