3. Consumption control
To make the available energy last as long as possible, smart power management is needed. The ACPI is a key element of clever power management. It is integrated into the operating system and communicates with the SBM3. The ACPI controls the total energy consumption via defined Power States. Individual components of the device, such as I/O or HD, can be switched off selectively via Device Power States, the S-States define various levels of sleep modes and the C-States regulate the CPU power. Here lies a wide field of opportunities to influence the power consumption.
Communication with the battery subsystem works the same as in commercial notebooks, via so-called control methods in the ACPI BIOS. For this reason, such a battery solution is referred to as CMB, Control Method Battery. As the name suggests, the software interface to the battery system consists of individual ACPI functions, the Control Methods. The two most important are _BIF (Battery Information) and _BST (Battery Status). _BIF sends static battery information, such as serial number, design voltage and model number to the ACPI OS. _BST, on the other hand, provides dynamically changing battery data such as charge status or remaining capacity. These methods are implemented in the congatec ACPI BIOS and provide the link between the operating system and the battery hardware. In addition, there is an event handler that needs to quickly respond to any changes in the battery condition. This handler is also implemented in the congatec ACPI BIOS and ensures that the operating system is notified of any change in