minerva/hardware/maixduino/MICROPYTHON_QUIRKS.md

MicroPython/MaixPy Quirks and Compatibility Notes

Date: 2025-12-03 MicroPython Version: v0.6.2-89-gd8901fd22 on 2024-06-17 Hardware: Sipeed Maixduino (K210)

This document captures all the compatibility issues and workarounds discovered while developing the voice assistant client for Maixduino.

---

String Formatting

❌ F-strings NOT supported

# WRONG - SyntaxError
message = f"IP: {ip}"
temperature = f"Temp: {temp}°C"

✅ Use string concatenation

# CORRECT
message = "IP: " + str(ip)
temperature = "Temp: " + str(temp) + "°C"

---

Conditional Expressions (Ternary Operator)

❌ Inline ternary expressions NOT supported

# WRONG - SyntaxError
plural = "s" if count > 1 else ""
message = "Found " + str(count) + " item" + ("s" if count > 1 else "")

✅ Use explicit if/else blocks

# CORRECT
if count > 1:
    plural = "s"
else:
    plural = ""
message = "Found " + str(count) + " item" + plural

---

String Methods

❌ decode() doesn't accept keyword arguments

# WRONG - TypeError: function doesn't take keyword arguments
text = response.decode('utf-8', errors='ignore')

✅ Use positional arguments only (or catch exceptions)

# CORRECT
try:
    text = response.decode('utf-8')
except:
    text = str(response)

---

Display/LCD Color Format

❌ RGB tuples NOT accepted

# WRONG - TypeError: can't convert tuple to int
COLOR_RED = (255, 0, 0)
lcd.draw_string(10, 50, "Hello", COLOR_RED, 0)

✅ Use bit-packed integers

# CORRECT - Pack RGB into 16-bit or 24-bit integer
def rgb_to_int(r, g, b):
    return (r << 16) | (g << 8) | b

COLOR_RED = rgb_to_int(255, 0, 0)
lcd.draw_string(10, 50, "Hello", COLOR_RED, 0)

---

Network - WiFi Module

❌ Standard network.WLAN NOT available

# WRONG - AttributeError: 'module' object has no attribute 'WLAN'
import network
nic = network.WLAN(network.STA_IF)

✅ Use network.ESP32_SPI for Maixduino

# CORRECT - Requires full pin configuration
from network import ESP32_SPI
from fpioa_manager import fm

# Register all 6 SPI pins
fm.register(25, fm.fpioa.GPIOHS10, force=True)  # CS
fm.register(8, fm.fpioa.GPIOHS11, force=True)   # RST
fm.register(9, fm.fpioa.GPIOHS12, force=True)   # RDY
fm.register(28, fm.fpioa.GPIOHS13, force=True)  # MOSI
fm.register(26, fm.fpioa.GPIOHS14, force=True)  # MISO
fm.register(27, fm.fpioa.GPIOHS15, force=True)  # SCLK

nic = ESP32_SPI(
    cs=fm.fpioa.GPIOHS10,
    rst=fm.fpioa.GPIOHS11,
    rdy=fm.fpioa.GPIOHS12,
    mosi=fm.fpioa.GPIOHS13,
    miso=fm.fpioa.GPIOHS14,
    sclk=fm.fpioa.GPIOHS15
)

nic.connect(SSID, PASSWORD)

❌ active() method NOT available

# WRONG - AttributeError: 'ESP32_SPI' object has no attribute 'active'
nic.active(True)

✅ Just use connect() directly

# CORRECT
nic.connect(SSID, PASSWORD)

---

I2S Audio

❌ record() doesn't accept size parameter only

# WRONG - TypeError: object with buffer protocol required
chunk = i2s_dev.record(1024)

✅ Returns Audio object, use to_bytes()

# CORRECT
audio_obj = i2s_dev.record(total_bytes)
audio_data = audio_obj.to_bytes()

Note: Audio data often comes in unexpected formats:

• Expected: 16-bit mono PCM
• Reality: Often 32-bit or stereo (4x expected size)
• Solution: Implement format detection and conversion

---

Memory Management

Memory is VERY limited (~6MB total, much less available)

Problems encountered:

• Creating large bytearrays fails (>100KB can fail)
• Multiple allocations cause fragmentation
• In-place operations preferred over creating new buffers

❌ Creating new buffers

# WRONG - MemoryError on large data
compressed = bytearray()
for i in range(0, len(data), 4):
    compressed.extend(data[i:i+2])  # Allocates new memory

✅ Work with smaller chunks or compress during transmission

# CORRECT - Process in smaller pieces
chunk_size = 512
for i in range(0, len(data), chunk_size):
    chunk = data[i:i+chunk_size]
    process_chunk(chunk)  # Handle incrementally

Solutions implemented:

1. Reduce recording duration (3s → 1s)
2. Compress audio (μ-law: 50% size reduction)
3. Stream transmission in small chunks (512 bytes)
4. Add delays between sends to prevent buffer overflow

---

String Operations

❌ Arithmetic in string concatenation

# WRONG - SyntaxError (sometimes)
message = "Count: #" + str(count + 1)

✅ Separate arithmetic from concatenation

# CORRECT
next_count = count + 1
message = "Count: #" + str(next_count)

---

Bytearray Operations

❌ Item deletion NOT supported

# WRONG - TypeError: 'bytearray' object doesn't support item deletion
del audio_data[expected_size:]

✅ Create new bytearray with slice

# CORRECT
audio_data = audio_data[:expected_size]
# Or create new buffer
trimmed = bytearray(expected_size)
trimmed[:] = audio_data[:expected_size]

---

HTTP Requests

❌ urequests module NOT available

# WRONG - ImportError: no module named 'urequests'
import urequests
response = urequests.post(url, data=data)

✅ Use raw socket HTTP

# CORRECT
import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host, port))

# Manual HTTP headers
headers = "POST /path HTTP/1.1\r\n"
headers += "Host: " + host + "\r\n"
headers += "Content-Type: audio/wav\r\n"
headers += "Content-Length: " + str(len(data)) + "\r\n"
headers += "Connection: close\r\n\r\n"

s.send(headers.encode())
s.send(data)

response = s.recv(1024)
s.close()

Socket I/O errors common:

• [Errno 5] EIO - Buffer overflow or disconnect
• Solutions:
  • Send smaller chunks (512-1024 bytes)
  • Add delays between sends (time.sleep_ms(10))
  • Enable keepalive if supported

---

Best Practices for MaixPy

1. Avoid complex expressions - Break into simple steps
2. Pre-allocate when possible - Reduce fragmentation
3. Use small buffers - 512-1024 byte chunks work well
4. Add delays in loops - Prevent watchdog/buffer issues
5. Explicit type conversions - Always use str(), int(), etc.
6. Test incrementally - Memory errors appear suddenly
7. Monitor serial output - Errors often give hints
8. Simplify, simplify - Complexity = bugs in MicroPython

---

Testing Methodology

When porting Python code to MaixPy:

1. Start with simplest version (hardcoded values)
2. Test each function individually via REPL
3. Add features incrementally
4. Watch for memory errors (usually allocation failures)
5. If error occurs, simplify the last change
6. Use print statements liberally (no debugger available)

---

Hardware-Specific Notes

Maixduino ESP32 WiFi

• Requires manual pin registration
• 6 pins must be configured (CS, RST, RDY, MOSI, MISO, SCLK)
• Connection can be slow (20+ seconds)
• Stability improves with smaller packet sizes

I2S Microphone

• Returns Audio objects, not raw bytes
• Format is often different than configured
• May return stereo when mono requested
• May return 32-bit when 16-bit requested
• Always implement format detection/conversion

BOOT Button (GPIO 16)

• Active low (0 = pressed, 1 = released)
• Requires pull-up configuration
• Debounce by waiting for release
• Can be used without interrupts (polling is fine)

---

Resources

• MaixPy Documentation: https://maixpy.sipeed.com/
• K210 Datasheet: https://canaan.io/product/kendryteai
• ESP32 SPI Firmware: https://github.com/sipeed/MaixPy_scripts/tree/master/network

---

Summary of Successful Patterns

# Audio recording and transmission pipeline
1. Record audio → Audio object (128KB for 1 second)
2. Convert to bytes → to_bytes() (still 128KB)
3. Detect format → Check size vs expected
4. Convert to mono 16-bit → In-place copy (32KB)
5. Compress with μ-law → 50% reduction (16KB)
6. Send in chunks → 512 bytes at a time with delays
7. Parse response → Simple string operations

# Total: ~85% size reduction, fits in memory!

This approach works reliably on K210 with ~6MB RAM.

---

Last Updated: 2025-12-03 Status: Fully tested and working