B404X Power Consumption Regression with SARA R410/R510

[grahamPatico]

Power Consumption Regression on Boron B404X with SARA R410/R510 Modem (Device OS 6.2.1 and 5.5.0)

Overview

Recent versions of Device OS (6.2.1 and 5.5.0) exhibit significantly increased and inconsistent power consumption on Boron B404X devices using the u-blox SARA R410/R510 modem. Compared to stable behavior on earlier firmware (pre-September 2023), current draw is up to 8× higher, severely impacting battery-powered deployments.

https://community.particle.io/t/brn404x-with-device-os-6-2-1-5-5-0-8x-and-highly-fluctuation-power-consumption/68802/48

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Affected Platform

• Hardware: Particle Boron B404X
• Modem: u-blox SARA R410 / R510
• Device OS Versions: 6.2.1, 5.5.0
• Expected Behavior: Stable ~9mA idle current
• Observed Behavior: ~70mA idle, with brief drops to ~27mA or ~5mA

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Key Findings

1. Power Behavior

• Idle current remains at ~70mA with random dips to ~27mA or lower.
• Calling any Particle.function() or Particle.publish() triggers a temporary reduction to ~27mA, which then rises again within seconds or minutes.
• Earlier firmware maintained a stable idle current around ~9mA.

2. Root Cause Indicators

Power-saving inconsistencies appear to be related to the UPSV=1 (ultra-low power) mode handling:

a. UPSV Mode Instability

// hal/network/ncp_client/sara/sara_ncp_client.cpp
// Lines 1589–1591
// XXX: R510 UPSV=1 appears to have issues dropping into low power mode

b. RXD Pin Activity (Every ~1.28s)

// hal/src/nRF52840/sleep_hal.cpp
// Lines 690–693
// RXD pin toggles HI-Z ~1ms after CTS goes HIGH, causing spurious wakeups

c. Keepalive Configuration Conflicts

// hal/network/ncp_client/sara/sara_ncp_client.cpp
// Line 105
const auto UBLOX_NCP_KEEPALIVE_PERIOD_R510 = UBLOX_NCP_KEEPALIVE_PERIOD_DISABLED;

d. PPP Client UPSV Behavior

// hal/network/lwip/ppp_client.cpp
// Lines 154–155
// Enables UPSV=1 after ~9 seconds idle

3. Recent Change

• The UPSV=1 mode was introduced/modified in [PR #2674](Enables UPSV=1 low power mode for R510 when idle for >=9.2s #2674), as noted in CHANGELOG.md.

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Steps to Reproduce

1. Flash Tinker or any test firmware to a Boron B404X running Device OS 6.2.1.
2. Connect to the Particle Cloud and allow the device to idle.
3. Measure current draw using a power profiler:
   • ~70mA idle
   • Drops to ~27mA temporarily when calling any Particle.function()
   • Returns to 70mA after 10 seconds to several minutes

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Recommended Actions

🔧 Short-Term Workaround

Explicitly disable UPSV to restore stable behavior:

Cellular.command("AT+UPSV=0");

🛠 Engineering Review

• Reassess UPSV idle timer implementation and regression since PR Enables UPSV=1 low power mode for R510 when idle for >=9.2s #2674.
• Investigate the RXD pin glitch (~1.28s interval) and its impact on modem wakeups.
• Review keepalive and PPP client settings for unintended state transitions.
• Consider conditionally reverting UPSV=1 mode for R410/R510 until fully stabilized.

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Impact

This regression causes a dramatic increase in power consumption for battery-powered devices, reducing expected battery life by up to 8×. For applications such as field deployments, remote sensing, and wildlife monitoring (e.g., OcuTrap), this presents a major operational and commercial challenge.

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Request for Review

We’d appreciate support from the Particle engineering team or guidance from other developers who may be experiencing similar issues. I am happy to share detailed logs, test scenarios, and additional profiling data.

Thank you,
Graham Patterson