Split transaction protocol for a bus system

A method for scheduling communication of data between a host and an agent, the method comprising:

• informing a host controller of the host of a data transfer capability of each endpoint of the agent;
• building a budget list for each endpoint of the agent, the budget list providing an earliest time a transfer between the hub and the end point is to occur and a latest time a result associated with the transfer is to be available;
• scheduling a first transaction of a split transaction between the host controller and the hub, the first transaction being scheduled to occur one unit time period before a first respective unit time period during which the transfer is to occur according to the earliest time of the budget list;
• and
• scheduling a second transaction of the split transaction between the host controller and the hub, the second transaction being scheduled one unit time period after a second respective unit time period during which the transfer is to finish according to the latest time of the budget list.

A digital system comprising:

• a host controller to schedule a split transaction to transfer data between the host controller and an endpoint of an agent via a hub;
• a device driver that operates the host controller to build a budget list for each endpoint of the agent, the budget list providing an earliest time a transfer between the hub and the end point is to occur and a latest time a result associated with the transfer is to be available;
• wherein the host controller is to:
• schedule a first transaction of a split transaction between the host controller and the hub, the first transaction being scheduled to occur one unit time period before a first respective unit time period during which the transfer is to occur according to the earliest time of the budget list;
• schedule a second transaction of the split transaction between the host controller and the hub, the second transaction being scheduled one unit time period after a second respective unit time period during which the transfer is to finish according to the latest time of the budget list;
• and
• schedule a third transaction to occur while the transfer is being performed.

An input/output peripheral device comprising:

• a hub with a hub controller;
• and
• a host coupled to the hub controller, the host having a host controller to schedule a split transaction to transfer data between the host and an agent via the hub, the split transaction being scheduled based on a budget list for each endpoint of the agent, the budget list providing an earliest time a transfer between the hub controller and the end point is to occur and a latest time a result associated with the transfer is to be available;
• wherein the host controller is operable to:
• schedule a first transaction of the split transaction between the host and the hub, the first transaction being scheduled to occur one unit time period before a first respective unit time period during which the transfer to occur according to the earliest time of the budget list;
• schedule a second transaction of the split transaction between the host and the hub, the second transaction being scheduled one unit time period after a second respective unit time period during which the transfer to finish according to the latest time of the budget list;
• and
• schedule a third transaction to occur while the transfer is being performed.