Bus guardian as well as method for monitoring communication between and among a number of nodes, node comprising such bus guardian, and distributed communication system comprising such nodes
In order to provide a bus guardian ( 30 ) for monitoring communication between and among a number of nodes ( 100 ), in particular between and among a number of electronic control units, the bus guardian ( 30 ) being designed for monitoring at least one cyclic time-triggered communication media access schedule for transmitting messages between and among the nodes ( 100 ) across at least one communication media ( 10 ), in particular across at least one channel ( 12 ) and across at least one optional further channel ( 14 ), and being assigned to at least one communication controller ( 40 ), the communication controller ( 40 ) comprising the communication media access schedule, wherein the bus guardian ( 30 ) as well as a corresponding method require neither any a priori knowledge of the communication schedule nor any configuration parameter and monitor the communication media access schedule of the communication controller ( 40 ) even during start-up of the communication, it is proposed that that the bus guardian ( 30 ) is able to learn, in particular within the first cycle, about said communication media access schedule, and that the bus guardian ( 30 ) makes use of the learned knowledge with respect to at least one possible schedule violation (SV 1 , SV 2 , SV 3 ), in particular with respect to at least one deviation from said communication media access schedule, for example during start-up of the communication.
1. A method for monitoring communication among a plurality of nodes, the method comprising:
assigning a communication media access schedule to a communication controller;
transmitting messages among the plurality of nodes based on the assigned communication media access schedule;
monitoring, with a bus guardian, the assigned communication media access schedule during start-up of a communication without using any configuration parameters;
learning, with the bus guardian, the assigned communication media access schedule; and
using the learned communication media access schedule to detect a schedule violation.
2. The method according to claim 1 , further comprising:
waking up the bus guardian after providing the bus guardian with a reset signal from any state;
starting up the bus guardian after providing the bus guardian with a first falling edge of an arming signal from the communication controller;
having the bus guardian enter a guarding mode after providing the bus guardian with a second falling edge of the arming signal; and
having the bus guardian enter a fail silent mode upon detection of the schedule violation.
3. The method according to claim 2 , wherein the waking up step further comprises:
enabling a bus driver;
detecting a first type of the schedule violation after a predetermined amount of negative edges of a transmit (TxEN) signal from the communication controller to the bus driver as well as to the bus guardian or upon a negative edge of said TxEN signal, while a receive (RxEN) signal, from the bus driver to and from the communication controller, is on a logical low state, or when said TxEN signal is on the logical low state for a predetermined time period, or when a clock unit being assigned to the bus guardian stops.
4. The method of claim 3 , wherein the at least one predetermined time period is no more than six microseconds.
5. The method according to claim 3 , wherein the starting up step further comprises:
enabling the bus driver to count clock cycles in order to learn about a cycle time;
counting the clock cycles until a first falling edge of said TxEN signal, wherein a frame comprises all information transmitted in a slot with an identifier on a channel; and
detecting a second type of the schedule violation after a predetermined amount of negative edges of said TxEN signal, or upon a negative edge of said TxEN signal, while said RxEN signal is on the logical low state, or when said TxEN signal is on the logical low state for the predetermined time period or when the clock cycle is longer than a certain timeout, or when the clock unit stops.
6. The method according to claim 5 , wherein the entering the guarding mode step further comprises:
enabling the bus driver to count clock cycles in order to supervise the cycle time; and
detecting a third type of the schedule violation upon a certain negative edge of the TxEN signal, or upon a negative edge of said TxEN signal, while said RxEN signal is on the logical low state, or when said TxEN signal is on the logical low state for at least one predetermined time period or when the cycle time deviates more than a predetermined margin from at least one learned cycle time, or when a time span between respective falling edges of the arming signal and of the TxEN signal deviates more than a predetermined margin from a time span learned during said starting step, or when the clock unit stops.
7. The method of claim 5 , wherein the at least one predetermined time period is greater than 2.047 microseconds.
8. The method of claim 5 , wherein the certain timeout is about sixteen milliseconds.
9. The method according to claim 2 , wherein the entering the fail silent mode step further comprises:
disabling the bus driver; and
only monitoring the reset input signal.
10. The method of claim 1 , further comprising:
ensuring error containment in a time domain of a node.
11. The method of claim 10 , further comprising:
correcting differences in clock offsets.
12. The method of claim 10 , further comprising:
correcting differences in clock rates.
13. The method of claim 1 , wherein a linear bus topology is used.
14. The method of claim 1 , wherein a star bus topology is used.
15. A communication apparatus, the apparatus comprising:
a power supply unit;
a host unit;
a communication controller;
a bus driver; and
a bus guardian, wherein the bus guardian learns a communication media access schedule, uses the learned communication media access schedule to detect a schedule deviation, and monitors the communication media access schedule during start-up of a communication without using any configuration parameters.
16. The apparatus of claim 15 , further comprising:
a voltage regulator connected to the power supply unit.
17. The apparatus of claim 15 , further comprising:
a voltage regulator connected to the host unit.
18. The apparatus of claim 15 , further comprising:
a voltage regulator connected to the communication controller.
19. The apparatus of claim 15 , further comprising:
a voltage regulator connected to the bus driver.
20. The apparatus of claim 15 , wherein a linear bus topology is used.
21. The apparatus of claim 15 , wherein a star bus topology is used.
22. A method for monitoring communication among a plurality of nodes, the method comprising:
assigning a communication media access schedule to a communication controller;
transmitting messages among the plurality of nodes based on the assigned communication media access schedule;
monitoring the assigned communication media access schedule by means of a bus guardian, wherein the bus guardian monitors the communication media access schedule during start-up of a communication without use of any configuration parameters;
using the monitored communication media access schedule to distinguish between allowed and forbidden deviations.