COM Port Management

When to Use

• •Before running idf.py flash or idf.py monitor
• •When flashing fails with PermissionError(13, 'Access is denied.') or could not open port 'COMx'
• •After a previous monitor session was interrupted or crashed

Step 1: Identify the COM Port

// turbo
[System.IO.Ports.SerialPort]::GetPortNames()

The board typically appears as COM5 (check Device Manager if unsure).

Step 2: Check for Processes Holding the Port

Stale Python processes from previous idf.py monitor sessions are the most common cause:

// turbo
Get-Process -Name python -ErrorAction SilentlyContinue | Select-Object Id, ProcessName, StartTime | Format-Table -AutoSize

Step 3: Kill Stale Processes

Kill Python processes older than a few minutes (these are leftover monitor/flash sessions):

Get-Process -Name python -ErrorAction SilentlyContinue | Where-Object { $_.StartTime -lt (Get-Date).AddMinutes(-5) } | Stop-Process -Force -PassThru | Select-Object Id, ProcessName

NOTE: Only kill processes older than 5 minutes to avoid killing active builds. Adjust the threshold as needed.

Step 4: Verify Port is Free

Try opening the port briefly:

// turbo
try {
    $port = New-Object System.IO.Ports.SerialPort "COM5", 115200
    $port.Open()
    $port.Close()
    Write-Host "COM5 is available"
} catch {
    Write-Host "COM5 is still locked: $($_.Exception.Message)"
}

Common Causes