Masked Registers¶

Masked registers were introduced to pack indepedend information to one 16-bit register. To extract information user has to apply correct mask by using and logic operator (\(\land\)) and shift operator (\(\Rightarrow\)).

Masked Register Example¶

Fuse state for EC/3V/Roof fans, information can be read from 4 bits.

Parameter name	Description	Shift	Mask	Value
FAN_ROOF	Fan roof fuse state	0	15	fuse_condition
FAN_EC	Fan EC fuse state	4	240	fuse_condition
FAN_3V	Fan 3V fuse state	8	3840	fuse_condition

Note

Table shows indepedend information that can be extraced from this register. Value column points to expected return values and their interpretation.

fuse_condition

Parameter name	Description	Value
NOT_SET	Not set.	0
FUSE_OK	Fan fuse is OK	1
FUSE_BLOWN	Fan fuse is BLOWN.	2

Note

Table shows how to interpret information after applying mask and shift.

How to extract values¶

assumption: Device returned value 4384 from masked register example.
task: Extract FAN_EC fuse condition.

Math representation¶

\begin{gather*} value \land mask \Rightarrow shift = result\\ 4384 \land 240 \Rightarrow 4 = 2 \end{gather*}

Python implementation¶

def extract_masked_value(value, mask, shift):
    return (value & mask) >> shift

C implementation¶

uint16_t extract_masked_value(uint16_t value, uint16_t mask, uint16_t shift) {
    return ((value & mask) >> shift);
};

Lastly interpret recived value according to fuse_condition table.

FUSE_BLOWN

Fan fuse is BLOWN.

Tip

Depending on how the information is split through the register it might be easier to read in a hexadecimal format. From our example 4384 can be represented as hex 0x1120 (0 - NOT_SET, 1 - FUSE_OK etc.). Presenting value in hex format helps when information is written on nibbles, binary format is more suitable for information written on bits.

Formatting temperature

API Reference