Analog to Digital (ADC)

Location: examples/PlatformSpecific/SOMRT1061/ADC_Simple

Supported Platforms: SOMRT1061

Simple A/D Example for SOMRT1061

This example demonstrates analog-to-digital conversion on the NetBurner SOMRT1061 platform using two different approaches: the simplified PinIO analog functions and direct register-level ADC control.

Overview

The application reads 8 analog input channels and displays both raw hexadecimal sample values and calculated decimal voltages. Output is sent to the serial console at approximately 5 Hz.

File Structure

SimpleAD/
|-- main.cpp      - Application entry point and main loop
|-- SimpleAD.cpp  - Low-level ADC driver implementation
|-- SimpleAD.h    - ADC driver function declarations

Hardware Configuration

Analog Input Pins

Pin Index	ADC Module	ADC Channel	Physical Pin
Pins[40]	ADC1	Channel 5	AD0
Pins[41]	ADC1	Channel 6	AD1
Pins[42]	ADC1	Channel 7	AD2
Pins[43]	ADC1	Channel 8	AD3
Pins[44]	ADC2	Channel 9	AD4
Pins[45]	ADC2	Channel 10	AD5
Pins[46]	ADC2	Channel 11	AD6
Pins[47]	ADC2	Channel 12	AD7

ADC Specifications

• Resolution: 12-bit (0-4095)
• Reference Voltage: 3.3V (VREFH/VREFL)
• Sample Rate: ~5 samples per second (configurable)

Two Operating Modes

Mode 1: PinIO Analog Functions (Default)

Enabled when USE_PIN_IO_ANALOG is defined (default).

#define USE_PIN_IO_ANALOG 1

This mode uses the simplified PinIO class methods:

• analogPins[i].n() - Returns raw 12-bit sample value
• analogPins[i].v() - Returns voltage as formatted string with value

• analogPins[i].volts() - Returns voltage as floating-point value

  Advantages:**

• Simpler API
• Background continuous conversion for fast response

• Leaves ADC2 available for other uses

  Optional Features:**

// Enable synchronous sampling (wait for fresh sample each read)
analogPins[i].analogEnableSampleWait(true);
 
// Enable hardware averaging (improves effective resolution)
PinIO::analogSetAveraging(PinIO::ANALOG_AVG_4);

Mode 2: Direct Register Access

Enabled by commenting out or setting USE_PIN_IO_ANALOG to 0.

// #define USE_PIN_IO_ANALOG 1

This mode uses the functions in SimpleAD.cpp/h:

• InitSingleEndAD() - Initialize both ADC modules
• ADConfigCh(module, channel, enable) - Configure individual channels
• StartAD() - Trigger conversion on all configured channels
• ADDone() - Check if conversion is complete

• GetADResult(module, channel) - Read conversion result

  Advantages:**

• Uses both ADC1 and ADC2 simultaneously
• Full control over conversion timing
• Supports chained conversions via ADC_ETC

SimpleAD Driver Details

Initialization (InitSingleEndAD)

1. Enables ADC and XBAR peripheral clocks
2. Resets and configures ADC_ETC (External Trigger Controller)
3. Configures ADC1 and ADC2 with identical settings:
   • 12-bit resolution
   • Low power mode (higher input impedance)
   • Software trigger initially (for calibration)
   • Async clock always enabled
4. Runs calibration sequence on both ADC modules
5. Switches to hardware trigger mode
6. Configures trigger chains for ADC_ETC

ADC Configuration Settings

CFG Register:
- OVWREN  = 1  : Overwrite previous data
- REFSEL  = 0  : VREFH/VREFL reference
- ADHSC   = 0  : Normal speed conversion
- ADSTS   = 1  : 4 ADC clock sample period
- ADLPC   = 1  : Low power mode enabled
- ADIV    = 3  : Clock divider
- MODE    = 2  : 12-bit resolution
- ADICLK  = 0  : Peripheral clock source
 
GC Register:
- ADCO    = 0  : Single conversion (no continuous)
- AVGE    = 0  : Hardware averaging disabled
- DMAEN   = 0  : DMA disabled
- ADACKEN = 1  : Async clock enabled

Channel Configuration (ADConfigCh)

• Configures GPIO pin for analog input (disables pull-up/down)
• Sets up ADC_ETC trigger chain entry
• Supports up to 8 channels per ADC module
• Uses back-to-back conversion mode for efficiency

Conversion Flow

StartAD()
    |
    V
Clear Done/Error flags
    |
    V
Set SW_TRIG bit in TRIG[0].CTRL
    |
    V
ADC_ETC triggers chained conversions
    |
    V
ADDone() returns true when complete
    |
    V
GetADResult() reads from TRIG[n].RESULT registers

Console Output Format

The application outputs two lines per sample cycle:

0xNNN, 0xNNN, 0xNNN, 0xNNN, 0xNNN, 0xNNN, 0xNNN, 0xNNN,
X.XXXX, X.XXXX, X.XXXX, X.XXXX, X.XXXX, X.XXXX, X.XXXX, X.XXXX,

• Line 1: Raw hexadecimal ADC values (0x000 to 0xFFF)
• Line 2: Calculated voltage values (0.0000V to 3.3000V)

Notes

1. The PinIO analog methods use only ADC1, leaving ADC2 available for other purposes such as DMA-based sampling or dedicated sensor input.
2. When using direct register access mode, both ADC1 and ADC2 are used with synchronized triggering via ADC_ETC.
3. Available ADC channels are limited by DRAM usage on the SOMRT1061. The chAvail bitmask in SimpleAD.cpp defines which channels are available: channels 5-12 on both ADC modules.
4. For higher effective resolution, enable hardware averaging using PinIO::analogSetAveraging() with values:
   • ANALOG_AVG_4
   • ANALOG_AVG_8
   • ANALOG_AVG_16
   • ANALOG_AVG_32
5. The default continuous background conversion provides the fastest response time but returns slightly stale samples. Enable sample wait mode for guaranteed fresh samples at the cost of longer read times.