Backoff timer for in-band interrupt on an I3C bus
A process for a slave device on a serial data bus to make an in-band interrupt request to a master device includes checking whether a backoff time stored by a backoff timer has expired. When the backoff time has not expired, the slave device refrains from initiating the in-band interrupt request to the master device in response to a start condition on the serial bus. However, when the backoff time has expired, the slave device is permitted to initiate the in-band interrupt request to the master device in response to the start condition on the serial bus.
1 . A process for a slave device on a serial data bus to make an in-band interrupt request to a master device, comprising:
storing a backoff time in a backoff timer of the slave device, said backoff time specifying a delay following master device servicing of a first in-band interrupt request that the slave device must wait before initiating a second in-band interrupt request;
checking whether the backoff time stored by the backoff timer has expired;
when the backoff time has not expired, refraining from initiating the second in-band interrupt request to the master device in response to a start condition on the serial data bus; and
when the backoff time has expired, permitting initiating the second in-band interrupt request to the master device in response to the start condition on the serial data bus.
2 . The process of claim 1 , wherein storing comprises, in response to acknowledgement by the master device on the serial data bus of the first in-band interrupt request, resetting the backoff time stored by the backoff timer to a maximum value.
3 . The process of claim 2 , further comprising, when the backoff time has not expired:
in response to the start condition on the serial data bus, decrementing the backoff time stored by the backoff timer and continuing to refrain from initiating the second in-band interrupt request to the master device.
4 . The process of claim 3 , wherein decrementing the backoff time comprises decrementing by one in response to each subsequent start condition on the serial data bus.
5 . The process of claim 3 , wherein the backoff time is expired when the backoff time is decremented to zero.
6 . The process of claim 2 , wherein the maximum value is set by the master device.
7 . The process of claim 2 , wherein the maximum value is set in view of a bus access priority level assigned to the slave device.
8 . The process of claim 1 , wherein the start condition on the serial data bus indicates start of a bus arbitration process for multiple slave devices to request attention by the master device on the serial data bus.
9 . A slave device configured for communication with a master device over a serial data bus, comprising:
a backoff timer configured to store a backoff time, said backoff time specifying a delay following master device servicing of one in-band interrupt request that the slave device must wait before initiating a subsequent in-band interrupt request;
wherein the slave device is further configured to:
check whether the backoff time stored by the backoff timer has expired;
when the backoff time has not expired, refrain from initiating the subsequent in-band interrupt request to the master device in response to a start condition on the serial data bus; and
when the backoff time has expired, initiate the subsequent in-band interrupt request to the master device in response to the start condition on the serial data bus.
10 . The slave device of claim 9 , further configured to:
reset the backoff time stored by the backoff timer to a maximum value in response to acknowledgement by the master device on the serial data bus of said one in-band interrupt request.
11 . The slave device of claim 10 , further configured, when the backoff time has not expired, to:
decrement the backoff time stored by the backoff timer in response to the start condition on the serial data bus; and
continue to refrain from initiating the subsequent in-band interrupt request to the master device.
12 . The slave device of claim 11 , wherein the backoff time is expired when the backoff time is decremented to zero.
13 . The slave device of claim 11 , further configured to decrement the backoff time by one in response to each subsequent start condition on the serial data bus.
14 . The slave device of claim 10 , wherein the maximum value is set by the master device.
15 . The slave device of claim 10 , wherein the maximum value is set in view of a bus access priority level assigned to the slave device.
16 . The slave device of claim 9 , wherein the start condition on the serial data bus indicates start of a bus arbitration process for multiple slave devices to request attention by the master device on the serial data bus.
17 . A process, comprising:
initiating a first in-band interrupt request by a slave device to a master device over a serial data bus in response to a first start condition on the serial data bus;
receiving from the master device an acknowledgment of the first in-band interrupt request;
resetting by the slave device of a backoff timer to store a backoff time in response to the received acknowledgement;
wherein said backoff time specifies a delay following the acknowledgment of the first in-band interrupt request that the slave device must wait before initiating a second in-band interrupt request; and
waiting by the slave device for the backoff time stored by the backoff timer to expire before initiating a second in-band interrupt request by the slave device to the master device over the serial data bus in response to a second start condition on the serial data bus.
18 . The process of claim 17 , wherein the delay specified by the backoff time is a number of start conditions on the serial data bus which occur after the first start condition and before the second start condition.
19 . The process of claim 18 , wherein resetting comprises setting the backoff time to a maximum value for the number of start conditions and wherein waiting comprises decrementing the backoff time by one in response to each start condition on the serial data bus which occurs after the first start condition.
20 . The process of claim 19 , wherein the maximum value is set by the master device.
21 . The process of claim 19 , wherein the maximum value is set in view of a bus access priority level assigned to the slave device.
22 . The process of claim 17 , wherein the start condition on the serial data bus indicates start of a bus arbitration process for multiple slave devices to request attention by the master device on the serial data bus.