Method carried out in system including active stylus and sensor controller, sensor controller, and active stylus
A sensor controller includes a transmitter configured to transmit an uplink signal including a first partial signal and a second partial signal. The transmitter is configured to transmit the first partial signal by direct spreading using a first spread code and transmit the second partial signal by direct spreading using a second spread code which is different from the first spread code and which has an identical chip time length to the first spread code. An active stylus includes a receiver configured to receive an uplink signal including a first partial signal and a second partial signal. The receiver is configured to synchronize with the uplink signal by detecting the first partial signal using a first spread code and thereafter detect the second partial signal using a second spread code, which is different from the first spread code and has an identical chip time length to the first spread code.
1. A method carried out in a system including an active stylus and a sensor controller, the method comprising:
transmitting, by the sensor controller, a first variable-length command including data of a variable number of bits;
receiving, by the active stylus, an uplink signal having a variable time length;
detecting, by the active stylus, the first variable-length command by decoding the uplink signal having the variable time length up to a tail of the uplink signal having the variable time length; and
transmitting, by the active stylus, a downlink signal that depends on the first variable-length command.
2. The method according to claim 1 , wherein:
the first variable-length command has a length field representing the number of bits of the first variable-length command; and
the method comprises:
decoding, by the active stylus, a value of the length field in the first variable-length command and determining a time period during which to continue detecting the first variable-length command based on the decoded value of the length field.
3. The method according to claim 1 , wherein:
the first variable-length command includes one or more fields each having a predetermined bit length; and
each of the one or more fields includes a flag indicating whether there is a next field.
4. The method according to claim 1 , wherein:
the first variable-length command includes a plurality of fields each having a predetermined bit length;
each of the plurality of fields includes a flag indicating whether there is a next field and a cyclic redundancy check (CRC) field including an error detection value calculated from a bit train included in the field; and
the method comprises:
calculating, by the active stylus, a plurality of error detection values based on a bit train included in each of the plurality of fields of the first variable-length command, and comparing each of the calculated error detection values with a value included in a corresponding CRC field of the first variable-length command;
wherein the transmitting of the downlink signal is in response to determining that each of the calculated error detection values agrees with the value included in the corresponding CRC field, for all of the fields of the first variable-length command.
5. The method according to claim 1 , wherein:
the first variable-length command includes at least a first field and a second field, the second field following the first field; and
the method comprises:
transmitting, by the sensor controller, the second field continuously after the first field.
6. The method according to claim 1 , wherein:
the first variable-length command includes at least a first field and a second field, the second field following the first field; and
the method comprises:
transmitting, by the sensor controller, the second field for a predetermined time after the first field.
7. The method according to claim 1 , wherein:
the first variable-length command has an end field indicating a tail end of the first variable-length command; and
the method comprises:
detecting, by the active stylus, the end field of the first variable-length command and, in response to detecting the end field, ending the receiving of the uplink signal.
8. The method according claim 7 , comprising:
correlating, by the active stylus, a spread code and the uplink signal; and
detecting, by the active stylus, the end field if a peak value is not obtained as a result of the correlating of the spread code and the uplink signal.
9. The method according to claim 8 , comprising:
directly spreading, by the sensor controller, a bit train representing the first variable-length command with the spread code to obtain the uplink signal; and
after transmitting the uplink signal, detecting, by the sensor controller, the downlink signal for a period of time that is at least as long as the duration of the spread code.
10. A sensor controller, comprising:
a transmitter, which, in operation, transmits a first variable-length command including data of a variable number of bits, using an uplink signal having a variable time length; and
a receiver, which, in operation, receives from an active stylus a downlink signal that depends on the first variable-length command, wherein the active stylus detects the first variable-length command by decoding the uplink signal having the variable time length.
11. The sensor controller according to claim 10 , wherein:
the first variable-length command has a length field representing the number of bits of the first variable-length command.
12. The sensor controller according to claim 10 , wherein:
the first variable-length command includes one or more fields each having a predetermined bit length; and
each of the one or more fields includes at least one of:
a flag indicating whether there is a next field, or
a cyclic redundancy check (CRC) field including an error detection value calculated from a bit train included in the field.
13. The sensor controller according to claim 10 , wherein:
the uplink signal is generated by directly spreading a bit train representing the first variable-length command with a spread code; and
the receiver receives the downlink signal for a period of time, which is at least as long as the duration of the spread code, after the transmitter transmits the uplink signal.
14. An active stylus, comprising:
a receiver, which, in operation, receives an uplink signal having a variable time length;
a processor, which, in operation, detects a first variable-length command including data of a variable number of bits, by decoding the uplink signal up to a tail of the uplink signal; and
a transmitter, which, in operation, transmits a downlink signal that depends on the first variable-length command.
15. The active stylus according to claim 14 , wherein:
the first variable-length command has a length field representing the number of bits of the first variable-length command; and
the processor, in operation, decodes a value of the length field in the first variable-length command and determines a time period during which to continue detecting the first variable-length command based on the decoded value of the length field.
16. The active stylus according to claim 14 , wherein:
the first variable-length command includes one or more fields each having a predetermined bit length; and
each of the one or more fields includes a flag indicating whether there is a next field.
17. The active stylus according to claim 14 , wherein:
the first variable-length command includes a plurality of fields each having a predetermined bit length;
each of the plurality of fields includes a flag indicating whether there is a next field and a cyclic redundancy check (CRC) field including an error detection value calculated from a bit train included in the field;
the processor, in operation, calculates a plurality of error detection values based on a bit train included in each of the plurality of fields of the first variable-length command, and compares each of the calculated error detection values with a value included in a corresponding CRC field of the first variable-length command; and
in response to a determination that each of the calculated error detection values agrees with the value included in the corresponding CRC field, the transmitter transmits the downlink signal.
18. The active stylus according to claim 14 , wherein:
the first variable-length command has an end field indicating a tail end of the first variable-length command; and
the processor, in operation, detects the end field of the first variable-length command and, in response to detecting the end field, controls the receiver to end the receiving of the uplink signal.
19. The active stylus according claim 18 , wherein:
the processor, in operation, correlates a spread code and the uplink signal, and detects the end field if a peak value is not obtained as a result of the correlating of the spread code and the uplink signal.
20. The active stylus according to claim 18 , wherein:
the uplink signal is generated by directly spreading a bit train representing the first variable-length command with a spread code.