fix: HW CDC write()

[SuGlider]

Description of Change

When writing a stream of data to the HW CDC of S3/C3/C6/H2, the SoC looses some bytes and don't send them all.

This fix makes it work fine.

Tests scenarios

Using an Arduino Sketch and a Python script to test the data flow.
Run the sketch in the S3/C3/C6/H2 with HWCDC on Boot enabled.
Run the script in the USB Host computer. It will open the CDC port and run the test.

Arduino side:

// ESP32-C3 using HW Serial CDC on Boot enabled

bool testCase1(const String &data) {
  size_t receivedLen = data.length();
  size_t sendLen = 0;

  while (sendLen < receivedLen) {
    if (!Serial.write(data[sendLen++])) break;   // <<< if it fails sending a single byte, it will fail the whole test case
  }
  Serial.println("===");
  if (sendLen != receivedLen) {
    Serial0.printf("\r\n ===> T1::Error -- didn't send all data [%d of %d]\r\n", sendLen, receivedLen);
    return false;
  } else {
    return true;
  }
}

bool testCase2(const String &data) {
  size_t receivedLen = data.length();

  size_t sent = Serial.write(data.c_str(), receivedLen);
  Serial.println("===");
  if (sent != receivedLen) {
    Serial0.printf("\r\n ===> T2::Error -- didn't send all data [%d of %d]\r\n\r\n", sent, receivedLen);
    return false;
  }  else {
    return true;
  }
}

void setup() {
  Serial0.begin(115200);

  Serial.begin();
  Serial0.println("\r\nStarting... open Serial Monitor with CDC port.");
  while(!Serial) delay(100);
  Serial.println("\r\nCDC Started.");

  bool result = true;
  String testString = "0";
  for (int x = 0; x < 100; x++) {  // runs the test cases 100 times
    String testString = "0";
    for (int i = 0; i < 302; i++) {  // sends from 1 to 301 bytes per test
      result &= testCase1(testString);
      result &= testCase2(testString);
      if (!result) {
        Serial0.printf("Failed with %d bytes\r\n", i);
        break;
      }
      char c = testString.charAt(testString.length() - 1);
      c = c == '9' ? '0' : c + 1;
//      if(i > 22) c = '7'; inserts an error to test the python script
      testString += c;
    }
    if (!result) break;
    Serial0.print(x+1);
    Serial0.print(" ");
    if (((x+1) % 10) == 0) Serial0.println();
  }
  if (result) {
    Serial.println("OK");
    Serial0.println("\r\nSetup is done : SUCCESS!\r\n");
  }  else {
    Serial.println("ERROR!!!");
    Serial0.println("\r\n\t\t====> Setup is done : FAILED!\r\n");
  }
}

void loop() {}

Python side:

#! /c/Users/rocor/AppData/Local/Microsoft/windowsApps/python.exe


"""
	Python Script for testing ESP32 S3 + C3 Arduino issue #9378 
	ISSUE - HW CDC Write() with fast stream of data
"""

import serial
import re
import sys
import random
import time

print ("CDC App test for issue 9378")

def is_valid_sequence(s):
    # Initialize variables
    prev_digit = None
    valid = True

    # Iterate through each character in the string
    for char in s:
        if char.isdigit():
            digit = int(char)
            if prev_digit is None:
                # First digit
                if digit != 0:
                    valid = False
                    break
            else:
                # Check if the next digit is valid
                if digit != (prev_digit + 1) % 10:
                    valid = False
                    break
            prev_digit = digit
        elif char == "=":
            # Check if the sequence ends with "==="
            if s.endswith("==="):
                break
            else:
                valid = False
                break
        else:
            # Invalid character
            valid = False
            break

    return valid


try:
	# CDC same as SERIAL_8N1 - Arduino equivalent
	# Change 'com1' to what ever is your USB CDC serial device name (win/linux)
	# timeout=None means that it will work as a blocking read()
	# write() is blocking by default

	CDC = serial.Serial(port='com22', baudrate=115200)   # timeout=0.01 means non blocking! 
#	CDC.set_buffer_size(rx_size = 128, tx_size = 128)  ## comment it out to speed up processing
except:
	print("COM22: port is busy or unavailable")
	exit()

print(f"Serial port com22 opened successfully.")
#read first 2 lines
line = CDC.readline().decode("utf-8").strip()
print(line)   ### for debugging
line = CDC.readline().decode("utf-8").strip()
print(line)  ### for debugging
pattern = re.compile(r"(\d+)===")

Error = False
counter = 0

while True:
	# Adds some random delay... for testing
#	randomTime_ms = random.randint(0, 5)   ## comment it out to speed up processing
#	time.sleep(randomTime_ms / 1000)
	
	# Read a line from the serial port
	line = CDC.readline().decode("utf-8").strip()
#	print(line)  ### for debugging

	# Check if the line ends with "==="
	if line.endswith("==="):
		# Extract the counter and sequence
		match = pattern.match(line)
		if match:
			sequence = match.groups()
			# Count the number of digits (0 to 9) in the sequence
			num_digits = len(sequence[0])
			if is_valid_sequence(sequence[0]):
				if num_digits >  301: ### Arduino sketch sends up to 302 digits
					if counter % 2 == 1: ### Arduino sketch send the line twice (TestCase 1 and 2)
						### CDC output will match ESP32 UART0 output for user control
						### Python will process the OS buffer and stay behind the ESP32 counting
						print(f"{int(counter / 2) + 1} ", end='',sep='',flush=True)				
					counter += 1
					if counter % 20 == 0:
						print("")
#				print(f"Sequence: '{sequence[0]}', Number of Digits: {num_digits}")  ### for debugging
			else:
				print(f"==> BAD sequence '{sequence[0]}', length: {num_digits}")
				Error = True
				break
		else:
			print(f"Invalid format: '{line}'")
			Error = True
			break
	else:
		print(line)  ### for debugging
		if line != "OK":
			print(f"Incomplete line: '{line}'")
			Error = True
		break

if Error:
	print("    ERROR ....")
else:
	print("\n All Fine!")
sys.exit()  ## this will close the CDC connection and reset the ESP32-xx

Related links

Fix #9378

[github-actions]

	Warnings
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	Messages
📖	You might consider squashing your 5 commits (simplifying branch history).

👋 Hello SuGlider, we appreciate your contribution to this project!

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[SuGlider]

Let's wait for @TD-er to confirm that this PR fixes the issue.

[P-R-O-C-H-Y]

@SuGlider Is this ready to be reviewed? :)

[TD-er]

I have been running this code for a while now and it does seem to work fine.
Only issue might be when you try to set the TX or RX buffer twice while HWCDC is already active.
One shouldn't do this, but it may be hard to diagnose when the device is crashing immediately.
Maybe just documenting it is enough here?