3. Fan control

The C600 card is passively cooled when installed in a suitable chassis enclosure. Fans within the chassis housing the C600 card(s) need to deliver sufficient airflow to keep the cards below their maximum operational temperature threshold, removing up to 252 W per C600 card.

The airflow required to do this will depend on inlet temperature. Assuming the maximum permitted inlet temperature of 35°C, 30 cubic feet/minute (850 litres/min) will be required per card at maximum power dissipation. If the power consumption of the cards is capped lower, this airflow requirement will also be lower.

There are a number of thermal sensors on the C600 card which can be read over the SMBus interface. These are listed in the C600 SMBus specification. The maximum of the various board temperature sensors is also reported as a single value and it is recommended that the BMC uses this single value for fan control.

The BMC should poll the maximum temperature register (0x40) over the SMBus and increase or decrease the fan speed depending on the results. We recommend that the fan speeds should be increased if the reported temperature of any C600 card is 65°C or above, and the fan speeds should be decreased if the reported temperature of all C600 cards is 50°C or below.

The polling frequency and fan control increment/decrement tables will be chassis dependent.