source

pico_ada_c09_ad_converter

1.9.0

Chapter 9: read the Pico ADC as counts, microvolts and fixed-point volts

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1.9.0

Chapter 9 - AD Converter

Ada rewrite of the Freenove "AD Converter" lesson for the Raspberry Pi Pico.

The sketch on GP26 (ADC0) prints three representations of the same potentiometer on one UART line:

  • RP.ADC.Analog_Value - the 12-bit code (0 .. 4095)
  • RP.ADC.Microvolts - that code scaled by the HAL with a Float
  • Pico.Analog.Input.Volts - a 32-bit ordinary fixed-point subtype (delta 0.1 mV, 'Small => 2**(-16)), converted from the count by multiply-first / divide-second

The chapter is the notes I needed before that line made sense:

  • AGND and ADC_VREF are a filtered analogue pair, not a second isolated supply. ADC3 (VSYS/3) and ADC4 (the on-chip temperature sensor) are not available as general inputs.
  • The RP2040 ADC has dead zones at both rails. On my board the floor sits around 19 counts (~15 mV) and the ceiling around 4081. Software clamps those to Volts'First and Volts'Last.
  • Free_Running plus a 2 Hz Put_Line leaves stale samples in the FIFO. The sketch uses One_Shot.
  • The three columns are three conversions, not three formats of one sample. They may differ by a count or two.
  • Sketch_09_1_ADC is No_Return under the Jorvik profile. The handler logs on Ada.Text_IO and re-raises; the embedded runtime then halts. Fine for a sample you reset with BOOTSEL. SPARK would want an outer loop instead.

Built against rp2040_hal / the Pico BSP. Watch the UART with CoolTerm (or any 115200 8N1 terminal).

Read the full tutorial at Chapter 9 - AD Converter: three ways to read a voltage, GNATdoc documentation, SourceForge repository

Authors
Martin Krischik <krischik@users.sourceforge.net>
Maintainers
Martin Krischik <krischik@users.sourceforge.net>
Maintainer profiles
@krischik
Licenses
GPL-3.0-or-later
Website
https://pi-ada-tutorial.sourceforge.io/pico_ada_c09_ad_converter
Release archive
sourceforge.net/projects/pi-ada-tutorial/files/Alire/pico_ada_c09_ad_converter-1.9.0.tgz
Tags
raspberry, pi, pico, rp2040, tasking, light-tasking, ada2022, embedded
Executables
sketch_09_1_adc
Manifest
index/pi/pico_ada_c09_ad_converter/pico_ada_c09_ad_converter-1.9.0.toml
Build and platform metadata 3 fields
Build switches
{
  "*": {
    "ada_version": [
      "-gnat2022"
    ]
  },
  "development": {
    "compile_checks": "Warnings",
    "contracts": "Yes",
    "runtime_checks": "Overflow"
  },
  "release": {
    "compile_checks": "Warnings",
    "contracts": "No",
    "runtime_checks": "Default"
  },
  "validation": {
    "compile_checks": "Warnings",
    "contracts": "Yes",
    "runtime_checks": "Everything"
  }
}
Configuration
{
  "values": {
    "adacl_embedded": {
      "Event_Log_Buffer_Size": 0,
      "Variant": "no_tasking"
    },
    "embedded_rp2040": {
      "Board": "rpi_pico",
      "Max_CPUs": 2
    },
    "pico_xbsp": {
      "Event_Log_Output": "uart",
      "Variant": "tasking"
    },
    "rp2040_hal": {
      "Interrupts": "bb_runtimes",
      "Use_Startup": false
    }
  }
}
Additional origin data
{
  "hashes": [
    "sha256:602015ac330ab9af86cf450d69dab83e9f9b337dffeb09d4e54323b5f81177f0",
    "sha512:2fd2e1d6cc57067e942be039c97d41217ea200a0e3f247ee3c45c3f17bd9e94cb0c1cf46602866f859215ab3e0dc49fec582ff2f8c2515bd30685acf3d8f217f"
  ]
}