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Marshal

The standard System.Runtime.InteropServices.Marshal class is available in TinyCLR with two methods exposed: ReadInt32 and WriteInt32. Together they let you read and modify peripheral hardware registers directly — useful when a feature isn't surfaced through the managed API and you need bit-level control.

NuGet package: GHIElectronics.TinyCLR.Core (Marshal lives in System.Runtime.InteropServices).

warning

This is an advanced API. Writing the wrong value to a hardware register can hang the device, corrupt other peripherals, or make the chip unrecoverable. Use only when you know exactly which register you're touching and why. Validate against the chip's reference manual before each write.

Example: setting a GPIO output​

The example below reads the GPIO output data register for port B, sets bit 0 (pin PB0), and writes it back — driving PB0 high.

using System;
using System.Runtime.InteropServices;

// Address of GPIOB output data register on SC20xxx.
var pinPB0OutDataReg = (IntPtr)0x58020414;

var portValue = Marshal.ReadInt32(pinPB0OutDataReg) | (1 << 0);     // Set bit 0.
Marshal.WriteInt32(pinPB0OutDataReg, portValue);
warning

Reading a status register can have side effects. Some peripherals clear pending flags when you read their status register — so a probe-read can change the peripheral's behavior at runtime. Check the chip manual before reading a status register from observation code.

Disabling interrupts​

For very tight timing-critical sequences (bit-banging a protocol, an atomic register modify, etc.) you can briefly disable all interrupts. Re-enable them as soon as the critical section is done — leaving interrupts off too long starves networking, USB, timers, and everything else that runs on them.

using GHIElectronics.TinyCLR.Native;

var wasAlreadyDisabled = Interrupt.IsDisabled();

if (!wasAlreadyDisabled)
    Interrupt.Disable();

// Timing-critical code goes here — keep it short.

if (!wasAlreadyDisabled)
    Interrupt.Enable();

The "was already disabled" check preserves the existing interrupt state if the caller had them off — important if your function might be called from inside another critical section.

warning

Keep interrupt-disabled regions to microseconds, not milliseconds. Long stalls cause dropped UART/USB bytes, missed timer events, and network instability. If you find yourself needing a long protected section, the design probably needs a lock or a thread instead.

Accessible register regions​

TinyCLR restricts Marshal.ReadInt32 and WriteInt32 to peripheral register ranges only. An attempt to access an address outside the allowed regions throws an exception.

  • Analog-to-digital converters (ADC)
  • Controller Area Network (CANFD)
  • Digital-to-analog converter (DAC)
  • Digital camera interface (DCMI)
  • LCD-TFT Display Controller (LTDC)
  • Ethernet (ETH)
  • Flexible memory controller (FMC)
  • General-purpose I/O (GPIO)
  • Inter-integrated circuit (I²C) interface
  • Power control (PWR)
  • Advanced-control timers (TIM1, TIM8)
  • General-purpose timers (TIM2, TIM3, TIM4, TIM5, TIM12, TIM13, TIM14, TIM15, TIM16, TIM17)
  • Basic timers (TIM6, TIM7)
  • Quad-SPI interface (QUADSPI)
  • Secure digital input/output MultiMediaCard interface (SDMMC1)
  • Real-time clock (RTC)
  • Serial peripheral interface (SPI)
  • Universal synchronous/asynchronous receiver-transmitter (USART/UART)
  • USB On-The-Go (USB_OTG)
  • Watchdog (WDG)
  • Reset and Clock Control (RCC)
  • Voltage reference buffer (VREFBUF)

API reference​

NamespaceDescription
GHIElectronics.TinyCLR.NativeMarshal and unmanaged interop classes