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I2C support for libDaisy Nim wrapper

This module provides I2C (Inter-Integrated Circuit) communication support for the Daisy Audio Platform. It supports both master and slave modes, blocking and DMA transfers.

⚠️ IMPORTANT - Blocking vs DMA Functions:

• Blocking functions (write, read, writeRegister, readRegister) will stall the CPU while waiting for the I2C transaction to complete. This can cause audio glitches if called from the audio callback or main loop during audio processing.
• DMA functions (transmitDma, receiveDma) use Direct Memory Access to transfer data in the background without blocking the CPU. These are safe to use during audio processing if your buffers are in the correct memory region.

DMA Buffer Requirements:

• Buffers must be in D2 memory domain (not stack variables!)
• Use {.section: ".sram1_bss".} or allocate on heap
• Or use dsy_dma_clear_cache_for_buffer() before transfer (advanced)

DMA Availability:

• I2C1, I2C2, I2C3: Share a single DMA channel (only one can use DMA at a time)
• I2C4: No DMA support (use blocking functions only)

Example - Simple I2C master (blocking):

import nimphea, per/i2c, per/uart

var daisy = initDaisy()
var i2c = initI2C(I2C_1, D11(), D12(), I2C_400KHZ)

startLog()

# Scan for devices (BLOCKS - don't use in audio callback!)
var foundDevices: array[112, uint8]
let count = i2c.scan(foundDevices)
print("Found ")
print(count)
printLine(" devices")

# Write to device (BLOCKS)
var txData = [0x01'u8, 0xFF]
if i2c.write(0x48, txData) == I2C_OK:
  printLine("Write OK")

# Read from device (BLOCKS)
var rxData: array[4, uint8]
if i2c.read(0x48, rxData) == I2C_OK:
  printLine("Read OK")

Example - Register access (blocking):

# Write to register (BLOCKS)
discard i2c.writeRegister(0x3C, 0x00, 0xAF)

# Read from register (BLOCKS)
let (result, value) = i2c.readRegister(0x3C, 0x01)

Example - Non-blocking DMA transfer:

import nimphea, per/i2c

# DMA buffers MUST be in D2 memory, not on stack!
var txBuffer {.section: ".sram1_bss".}: array[64, uint8]
var transferComplete = false

proc onTransferComplete(context: pointer, result: I2CResult) {.cdecl.} =
  # Called from interrupt - keep this FAST!
  transferComplete = true

var daisy = initDaisy()
var i2c = initI2C(I2C_1, D11(), D12(), I2C_400KHZ)

# Start DMA transfer (non-blocking)
discard i2c.transmitDma(0x48, txBuffer, onTransferComplete, nil)

# CPU is free to do other work while transfer happens in background
while not transferComplete:
  # Do audio processing or other tasks
  discard