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;
determining, by the active stylus based on the first variable-length command, a time period during which the active stylus continues to detect the first variable-length command; and
transmitting, by the active stylus, a downlink signal according to the first variable-length command.
2 . The method according to claim 1 , wherein:
the first variable-length command includes a length field indicating the variable number of bits; and
the active stylus determines the time period based on the variable number of bits indicated in the length field.
3 . The method according to claim 1 , wherein:
the first variable-length command includes one or more fields, each field having a predetermined bit length and including 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 field having a predetermined bit length, including a flag indicating whether there is a next field, and including a cyclic redundancy check (CRC) field including an error detection value; and
the method comprises, for each of the plurality of fields of the first variable-length command:
calculating, by the active stylus, an error detection value from a bit train included in the field; and
comparing, by the active stylus, the calculated error detection value with the error detection value included in the CRC field of the field;
wherein, the active stylus transmits the downlink signal responsive to determining that each of the calculated error detection values agrees with the error detection value included in the CRC field of the field.
5 . The method according to claim 1 , wherein:
the first variable-length command includes at least a first field and a second field that follows 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 that follows the first field; and
the method comprises:
transmitting, by the sensor controller, the second field after a defined lapse of time after transmitting the first field.
7 . The method according to claim 1 , wherein:
the first variable-length command includes 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
responsive to detecting the end field, stopping, by the active stylus, the receiving of the uplink signal.
8 . The method according to 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 observed as a result of the correlating of the spread code and the uplink signal.
9 . The method according to claim 8 , comprising:
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 according to the first variable-length command, wherein the active stylus detects the first variable-length command by decoding the uplink signal.
11 . The sensor controller according to claim 10 , wherein:
the first variable-length command includes a length field indicating the variable 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 field having a predetermined bit length and including 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.
13 . The sensor controller according to claim 10 , wherein:
the sensor controller is configured to spread a bit train representing the first variable-length command with a spread code to generate the uplink signal; and
after the transmitter transmits the uplink signal, the receiver receives the downlink signal for a period of time that is at least as long as the duration of the spread code.
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;
determines, based on the first variable-length command, a time period during which the processor continues to detect the first variable-length command; and
a transmitter, which, in operation, transmits a downlink signal according to the first variable-length command.
15 . The active stylus according to claim 14 , wherein:
the first variable-length command includes a length field indicating the variable number of bits; and
the processor, in operation, determines the time period based on the variable number of bits indicated in the length field.
16 . The active stylus according to claim 14 , wherein:
the first variable-length command includes one or more fields, each field having a predetermined bit length and including 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 field having a predetermined bit length, including a flag indicating whether there is a next field, and including a cyclic redundancy check (CRC) field including an error detection value; and
the processor, for each of the plurality of fields:
calculates an error detection value from a bit train included in the field;
compares the calculated error detection value with the error detection value included in the CRC field of the field; and
controls the transmitter to transmit the downlink signal responsive to determining that each of the calculated error detection values agrees with the error detection value included in the CRC field of the field.
18 . The active stylus according to claim 14 , wherein:
the first variable-length command includes 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
responsive to detecting the end field, controls the receiver to stop the receiving of the uplink signal.
19 . The active stylus according to 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 observed as a result of the correlating of the spread code and the uplink signal.
20 . The active stylus according to claim 19 , wherein:
the processor, in operation, spreads a bit train representing the first variable-length command with the spread code to obtain the uplink signal.