Use OTP Feature flag to change ADC reference source

[scott-brust]

Problem

There are potentially many different platforms that may end up using the richtek DCDC part with the excessive ripple voltage. For already shipped BRN404X platforms, the HW_VERSION OTP field can be used to identify them. For other SKUs, we need a different method.

Solution

The HW Feature Flags bytes of HW INFO in OTP have bits available. However, the tracker platform uses all but one of these bits. We will use the last OTP feature flag bit to denote the presence of the RIchtek part, and thus the need to switch to the internal ADC reference voltage.

Steps to Test

1. Clear the OTP bit
2. Reboot, and the ADC should use the internal reference

Example App

#define PARTICLE_USE_UNSTABLE_API
#include "storage_hal.h"

void burnOTP(){
    const uintptr_t HW_DATA_OTP_ADDRESS = 0x00000022;

    uint8_t hwFeatures[] = {0x00, 0x00};
    int r = hal_storage_read(HAL_STORAGE_ID_OTP, HW_DATA_OTP_ADDRESS, hwFeatures, 2);
    Log.info("Read result: %d / %x %x", r, hwFeatures[0], hwFeatures[1]);

    // Clear bit 15 of the HW Feature Flags bytes
    hwFeatures[1] &= 0x7F;
    r = hal_storage_write(HAL_STORAGE_ID_OTP, HW_DATA_OTP_ADDRESS, hwFeatures, 2);
    Log.info("Write result: %d", r);

    r = hal_storage_read(HAL_STORAGE_ID_OTP, HW_DATA_OTP_ADDRESS, hwFeatures, 2);
    Log.info("Read result after writing: %d / %x %x", r, hwFeatures[0], hwFeatures[1]);
}

void setup()
{
    // Init the ADC HAL to force reading of the OTP bits
    hal_adc_read(D0);
}

void loop()
{
    if (!Serial.available()) {
        return;
    }

    auto ch {Serial.read()};

    switch (ch) {
    case '1':
        burnOTP();
        break;
    default:
        Serial.printf("Invalid selection\r\n");
        break;
    }

    hal_device_hw_info hwInfo = {};
    hal_get_device_hw_info(&hwInfo, nullptr);
    Log.info("Feature Bits: %08x Top byte %02x Low Byte %02x", 
        hwInfo.features, 
        (hwInfo.features & 0x0000FF00) >> 8,
        hwInfo.features & 0x000000FF);
}

Burning the bit should show this

0000017308 [app] INFO: Feature Bits: 0000ebfe Top byte eb Low Byte fe
0000017308 [app] INFO: Read result: 2 / fe eb
0000017309 [app] INFO: Write result: 2
0000017309 [app] INFO: Read result after writing: 2 / fe 6b
0000022312 [app] INFO: Feature Bits: 00006bfe Top byte 6b Low Byte fe

After reboot, the ADC source will be internal.

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[avtolstoy]

Double check endianness. Not saying this is incorrect, but a good idea to confirm it's actually bit 16 in how hal_get_device_hw_info() parses stuff and how things are provisioned.

[scott-brust]

hal_get_device_hw_info() Puts the bytes in the right spots, I can examine adcReference with debugger after HAL init and can see its detecting the cleared bit in the right spot:

(gdb) p adcReference
$1 = HAL_ADC_REFERENCE_INTERNAL