Flash Read and Write Experiment

1. Flash Filesystem Overview

A filesystem partition (FAT/LittleFS by default) is allocated in the internal Flash of the ESP32-S3. MicroPython can operate on files through the standard open() / read() / write() interfaces, and the data is retained after power-off. This experiment implements interactive Flash data management: append, read, delete, and clear.

Typical application scenarios:

2. Core Concepts

2.1 MicroPython Filesystem

MicroPython automatically mounts the Flash filesystem at startup. Under the root directory /, the standard Python file API (open / read / write) can be used for reading and writing.

2.2 Data Storage Format

In this experiment, the first line stores the total record count, and each subsequent line stores one user data entry. On the first run the file does not exist; the code automatically creates it and writes 0 on the first line. After the first append, the first line is updated to the actual record count:

0                    ← First created, count is 0
Hello ESP32-S3       ← 1st entry (the first line is updated to 1 after the append)
MicroPython Flash    ← 2nd entry
...

Each operation first reads all lines into a list, then writes everything back after adding/deleting — suitable for small data volumes (< tens of KB).

2.3 Core API

​x
# Open file
f = open(f_path, "w")    # Write mode (overwrite)
f = open(f_path, "r")    # Read mode
f = open(f_path, "a")    # Append mode
​
# Read & write
content = f.read()              # Read all content
lines = content.splitlines()   # Split into lines
f.write("hello\n")              # Write one line
f.close()                       # Close (must!)

3. Hardware Dependencies

This experiment only uses the internal Flash of the ESP32-S3, no external hardware required.

3.1 ESP32-S3 Hardware Features

4. Project Architecture and Flow

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Script execution (single-file .py)
  │
  ├─ Initialize: check whether the file exists; if not, create it and write the first-line count "0\n"
  ├─ Print the menu: [1 Append / 2 Read / 3 Delete / 4 Clear]
  │
  └─ while True:
       ├─ input()  wait for REPL command input
       │
       ├─ "1" Append:
       │    ├─ Read all lines → parse count (first line)
       │    ├─ count++ → append a new line
       │    └─ Write everything back to the file
       │
       ├─ "2" Read:
       │    ├─ Read all lines → skip count=0 or empty
       │    └─ Print line by line
       │
       ├─ "3" Delete a single entry:
       │    ├─ Enter the index → delete that line
       │    ├─ count-1, update the first line
       │    └─ Write back
       │
       └─ "4" Clear:
            └─ Write "0\n" (reset)

5. Source Code Details

Complete source code: 5.Source Collection → MicroPython → 3.Serial Communication and Storage System → 4. FLASH → flash_fs.py

5.1 File Initialization

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# Create the file if it does not exist
try:
    f = open(f_path, "r")
    f.close()
except:
    f = open(f_path, "w")
    f.write("0\n")       # First line = count
    f.close()

try/except is a reliable way to check whether a file exists — some MicroPython versions do not support os.path.exists().

5.2 Append Data (Command 1)

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# Read the current content
f = open(f_path, "r")
lines = f.read().splitlines()
f.close()
​
# Parse and update the counter
count = 0
if len(lines) > 0:
    count = int(lines[0])
count += 1
lines[0] = str(count)
​
# Append a new line
lines.append(input("Content: "))
​
# Write all lines back
f = open(f_path, "w")
for s in lines:
    f.write(s + "\n")
f.close()
print("Saved.")

5.3 Read All (Command 2)

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f = open(f_path, "r")
lines = f.read().splitlines()
f.close()
​
count = int(lines[0]) if len(lines) > 0 else 0
if count == 0 or len(lines) <= 1:
    print("No data.")
else:
    print("Flash data:")
    for i in range(1, len(lines)):
        print("%d: %s" % (i, lines[i]))

5.4 Delete a Single Entry (Command 3)

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num = int(input("Index: "))
f = open(f_path, "r")
lines = f.read().splitlines()
f.close()
​
if num < 1 or num >= len(lines):
    print("Invalid index.")
else:
    del lines[num]                  # Delete the line
    lines[0] = str(len(lines) - 1)  # Update the count
    with open(f_path, "w") as f:
        for s in lines:
            f.write(s + "\n")
    print("Deleted.")

5.5 Clear (Command 4)

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f = open(f_path, "w")
f.write("0\n")
f.close()
print("Cleared.")

6. Operation Procedure

6.1 Flashing and Running

Thonny IDE operation steps: See MicroPython → 1.Development Basics → 3.Thonny IDE.

1. Open flash_fs.py with Thonny IDE and click Run
2. Enter commands in the REPL/Shell area to interact (number 1~4 + Enter)

6.2 Expected Behavior

After startup, the program prints the menu and waits for user input. Enter the corresponding number to perform append/read/delete/clear operations. The data is saved in the Flash filesystem and remains after a soft reset or power-off.

Flash space is usually several MB; the first-line count method in this experiment is suitable for hundreds of entries of small data. For large amounts of data storage, it is recommended to write line by line in append mode.

6.3 Serial Output Example

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===== Internal Flash Test =====
1 Append 2 Read 3 Delete 4 Clear
1
Content: Temperature 25.5C
Saved.
1
Content: Humidity 60%
Saved.
1
Content: ESP-IDF
Saved.
2
Flash data:
1: Temperature 25.5C
2: Humidity 60%
3: ESP-IDF
3
Index: 1
Deleted.
2
Flash data:
1: Humidity 60%
2: ESP-IDF
4
Cleared.
2
No data.

Stored data before power-off:

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===== Internal Flash Test =====
1 Append 2 Read 3 Delete 4 Clear
1
Content: Temperature 25.5C
Saved.
1
Content: Humidity 60%
Saved.
1
Content: ESP-IDF
Saved.
2
Flash data:
1: Temperature 25.5C
2: Humidity 60%
3: ESP-IDF

Read after power-off and restart (data not lost):

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===== Internal Flash Test =====
1 Append 2 Read 3 Delete 4 Clear
2
Flash data:
1: Temperature 25.5C
2: Humidity 60%
3: ESP-IDF

6.4 Verification Method

7. Common Issues