Apparatus and method for communication on a serial bus
The present disclosure relates to a method comprising receiving edges conveyed by a serial bus and separated by multiples of a same duration, determining a measurement value of a ratio between a cycle time of a clock and the duration, and sending bits on the serial bus using the measurement value.
1. A method comprising:
receiving, by a first device, bus signal edges conveyed by a clockless serial bus and separated by multiples of a same duration, the duration being based on a second cycle time of a second clock of a second device sending the bus signal edges;
determining, by the first device, without using the second clock, a measurement value of a ratio between a first cycle time of a first clock of the first device and the duration, the determining comprising:
determining a first value representative of a sum of differences between the measurement value and an actual value of a ratio of cycles of the first clock of the first device occurring between two received bus signal edges; and
subtracting the first representative value from a stored value;
sending, by the first device, bits on the clockless serial bus using the measurement value.
2. The method according to claim 1 , wherein the receiving the bus signal edges is performed before the sending the bits.
3. The method according to claim 1 , further comprising receiving data using the measurement value, the bus signal edges comprising edges between bits of the received data.
4. The method according to claim 3 , further comprising sending an acknowledgement of receipt of the data using the measurement value.
5. The method according to claim 1 , further comprising keeping the stored value fixed during the sending the bits.
6. The method according to claim 1 , wherein the determining the measurement value comprises adding, to the stored value, a predetermined value and/or a calculated value calculated as a function of a temperature.
7. The method according to claim 6 , further comprising extrapolating the calculated value from a plurality of predefined pairs each comprising a temperature value and a second value corresponding to the calculated value for the temperature value.
8. The method according to claim 1 , further comprising, at each cycle of the first clock of the first device, integer-modulo adding a second value representative of the measurement value to a content of a register, the determining the first value being based on a difference in the content of the register between reception times of the two of the bus signal edges.
9. The method according to claim 8 , wherein the sending of each of the bits starts at a time at which the content of the register crosses a threshold.
10. The method according to claim 5 , wherein keeping the stored value fixed is implemented by a multiplexer that provides the stored value, an input among a first plurality of inputs of the multiplexer receiving the stored value, the input among a second plurality of inputs being selected during the sending of the bits.
11. A first device configured to:
receive bus signal edges conveyed by a clockless serial bus and separated by multiples of a same duration, wherein the duration is based on a second cycle time of a second clock of a second device sending the bus signal edges;
determine, without using the second clock, a measurement value of a ratio between a first cycle time of a first clock of the first device and the duration, wherein the first device configured to determine the measurement value comprises the first device configured to:
determine a first value representative of a sum of differences between the measurement value and an actual value of a ratio of cycles of the first clock of the first device occurring between two received bus signal edges; and
subtract the first representative value from a stored value; and
send bits on the clockless serial bus using the measurement value.
12. The first device according to claim 11 , wherein the first device is configured to be connected to the clockless serial bus.
13. The first device of claim 12 , wherein the first clock of the first device is disposed on a semiconductor substrate.
14. The first device according to claim 11 , configured to have a sleep state and a wake state, wherein a transition from the sleep state to the wake state is triggered by a frame conveyed by the clockless serial bus, wherein the frame comprises at least two consecutive cycles of a dominant state followed by a recessive state, and wherein the recessive states and dominant states have durations of between 2 and 5 times the duration.
15. The first device according to claim 11 , wherein the first device is configured to receive the bus signal edges before sending the bits.
16. The first device according to claim 11 , wherein the first device is configured to receive data using the measurement value, wherein the bus signal edges comprise edges between bits of the received data.
17. A system comprising:
a clockless serial bus; and
one or more first devices coupled to the clockless serial bus, each of the one or more first devices configured to:
receive bus signal edges conveyed by the clockless serial bus and separated by multiples of a same duration, the duration being based on a second cycle time of a second clock of a second device sending the bus signal edges;
determine, without using the second clock, a measurement value of a ratio between a first cycle time of a first clock of the first device and the duration;
determine a first value representative of a sum of differences between the measurement value and an actual value of a ratio of cycles of the first clock of the first device occurring between two received bus signal edges; and
subtract the first representative value from a stored value; and
send bits on the clockless serial bus using the measurement value.
18. The system of claim 17 , further comprising the second device coupled to the clockless serial bus, the second device configured to send:
first messages carrying a set of operations to be implemented by the first devices; and
second messages addressed to a part of the first devices, the second messages conveying respective identifiers of the first devices to which the second messages are respectively addressed, the second messages requesting from the first devices to which they are addressed to send respective reactions towards the second device within respective expected time intervals,
wherein the first devices are configured to:
receive the first messages, read the set of operations to be implemented, and implement operations as a function of the read set; and
receive the second messages, and react to the second messages by sending, within the respective expected time intervals, reactions towards the second device.