Dell PowerEdge XR8720t Installation and Service Manual
Heater Manager subsystem
Heater Manager subsystem
The XR8720t needs to support an operating temperature range of ‐20°C to 55°C with a non‐operational range of ‐40°C to 65°C. The following major components do not support an industrial range and may need to be heated before they can be powered on:
- Intel Xeon 6 SoC – minimum temperature is 0°C
- iDRAC temperature range of 0°C to 70°C
- CPLD temperature range of 0°C to 85°C
- DIMM memory – minimum temperature is 0°C
- M.2 drives – temperature range is 85°C with selected range of 0°C to 85°C
- Adapter cards – temperature ranges vary depending on the manufacturer.
- Heater power consumption consumes up to 470 W
Usage
The temperature probe and heater module assemblies will always be installed on the XR8720t.SubSystem details
The normal time to boot a system of a Linux OS prompt is in the order of 1 or 2 minutes. Because the system needs to heat before it can be booted, extra time is needed to get to the OS prompt. The total boot time for the system to the OS prompt (Linux) should not be longer than 6 minutes. This implies that the heating time must be less than 4 minutes.
In cold environments components need to be heated to an operational temperature range before they can be powered up. A small industrial range microcontroller (i.e., NXP MCXN546) called the Heater Manager subsystem is needed to measure the temperature via strategically placed temperature sensors and to apply current to one or more heating pads.
System heating is separated into a maximum of seven zones for different parts of the system. Each zone has one heating pads (connected in parallel) and one or more temperature sensors. Each zone can have a different minimum temperature but in general they are all the same and above 0C. The below table shows a potential list of heater modules in the Dell PowerEdge XR8720t.
| Heater Zone | Description |
|---|---|
| 1 | CPU‐Processor |
| 2 | DIMM A1 |
| 3 | DIMM A2 |
| 4 | iDRAC and FPGA |
| 5 | On-board M.2 drive |
| 6 | M.2 Drive 1 on the riser |
| 7 | M.2 Drive 0 on the riser |
Once the Heater Manager subsystem MCU (MCXN546) has power, it turns on the green heater LED (HM_SYS_PH_LED_N) and determines the temperature of each zone. Any zone below the threshold (e.g., 4°C) will have its heater turned on by a FET until the zone is up to temperature. The Heater Manager subsystem should continue to monitor the temperature and turn on the heater pad if the temperature ever drops below a threshold (e.g., 2°C). If no heating is required because the system is already above the heating thresholds, then the LED should still be flashed briefly for visible feedback that the system is in fact starting up. A jumper can be used to power the system without heating.
During heating, the Heater Manager subsystem may opt to use PWM to control the heating ramp and slow down rather than just turning the heater on and off. If the wattage is known for each heating zone, it is straightforward to estimate the energy that is used to heat each zone based on the time, PWM ratio, and wattage. Once all the zones are up to temperature, the “HM_SYSTEM_PH_OK_N” signal is used to turn on power to the rest of the system, and the green heater LED is turned off. iDRAC is connected to the Heater Manager subsystem with an I2C bus. IDRAC can gather metrics from the Heater Manager subsystem such as on/off time, energy that is used, and temperature statistics using the I2C interface. IDRAC may also want to query status such as zone name, zone temperature and errors.
Monitoring is added in each zone to ensure that the heating pad is present and that a FET is not shorted. A blinking amber heater LED (HM_SYSTEM_PH_FAULT_LED_N) indicates a problem with the heating sub‐system. This flashing LED is the only indication of a problem because iDRAC is not yet available for problem logging. Any failure in the heating system turns off power to the heater FETs, flashes the amber heater status LED, and initiates a system shutdown if the temperature starts to drop below the temperature threshold. If the ambient temperature is high enough (e.g., 10°C), then the iDRAC and shared NIC is powered to ensure that the problem is logged with iDRAC and is available on a remote iDRAC console.
Heater Manager subsystem LED
- LED lights Green when system pre‐heating is enabled and will turn off when system pre‐heating is completed. The Heater Manager subsystem will continue to maintain proper temperature on the system after preheating, but the LED will stay off while the system is on.
- LED flashes Amber with a 1 Hz frequency when any required heater or thermal sensor is absent or has failed.
When the OS is shut down, iDRAC enters state S5. The Heater Manager subsystem may turn on heaters as necessary. At low system temperatures iDRAC turn off the system fans to reduce the ingress of colder ambient air. Such as a zone not increasing its temperature when heated.