Transparent repeater device for handling displayport configuration data (DPCD)
Consistent with an example embodiment a repeater device is provided for handling signal transmissions, in particular in a DisplayPort environment. The repeater is to be coupled with an upstream device and a downstream device, the repeater being adapted for transmitting signals received from the upstream device to the downstream device and for conditioning the signals before transmission. The repeater is configured to provide a transparent communication path between the upstream device and the downstream device for DPCD access transactions belonging to a second group of DPCD access transactions. For DPCD access transactions belonging to a first group of DPCD access transaction, the repeater is configured to process the DPCD access transactions by accessing one or more DPCD registers included in the repeater.
1. A DisplayPort repeater circuit, comprising:
an upstream data interface;
a downstream data interface;
a plurality of DisplayPort configuration data (DPCD) registers, and
a control circuit coupled to the upstream data interface, the downstream data interface, and the plurality of DPCD registers, the control circuit configured to:
process DPCD access transactions received from the upstream data interface, which are included in a first list of DPCD access transactions, by accessing one or more of the plurality of DPCD registers; and
process DPCD access transactions received from the upstream data interface, which are included in a second list of DPCD access transactions, by providing a transparent communication path to forward the transactions to the downstream data interface.
2. The DisplayPort repeater circuit of claim 1 , wherein the control circuit is further configured to:
train one or more communication links on the upstream data interface and one or more communication links on the downstream data interface;
while training the communication links on the upstream and downstream data interfaces, process DPCD access transactions received from the upstream data interface, which are included in a list of link-training transactions, by accessing one or more of the plurality of DPCD registers; and
after training of the communication links on the upstream and downstream data interfaces, process DPCD access transactions received from the upstream data interface, which are included in the list of link-training transactions, by forwarding the DPCD access transactions to the downstream data interface.
3. The DisplayPort repeater circuit of claim 2 , wherein:
training the communication links on the upstream and downstream data interfaces sets the communication links to a first link rate; and
the control circuit is further configured to, in response to a failure to train one or more of the communication links on the upstream or downstream data interfaces, retrain the communication links on the upstream and downstream data interfaces to set the communication links to a second rate that is lower than the first rate.
4. The DisplayPort repeater circuit of claim 1 , wherein the control circuit is further configured to provide a transparent communication path between an upstream device coupled to the upstream data interface and a downstream device coupled to the downstream data interface for one or more DPCD access transactions included in the second list of DPCD access transactions.
5. The DisplayPort repeater circuit of claim 1 , wherein the second list of DPCD access transactions includes reserved DPCD access transactions.
6. The DisplayPort repeater circuit of claim 1 , wherein the control circuit is further configured to, in response to receiving a DPCD access transaction to a DPCD register not supported by the repeater, provide a transparent communication path to forward the DPCD access transaction to the downstream data interface.
7. The DisplayPort repeater circuit of claim 6 , wherein the symmetric links are configured to have the same link rate.
8. The DisplayPort repeater circuit of claim 2 , wherein one or more DPCD access transactions are included in the first list of DPCD access transactions and one or more DPCD access transactions are included in the second list of DPCD access transactions.
9. The DisplayPort repeater circuit of claim 2 , wherein training one or more communication links on the upstream data interface and one or more communication links on the downstream data interface configures the one or more links on the upstream and downstream data interfaces to comply with a DisplayPort link configuration supported by both the repeater circuit and the downstream device.
10. The DisplayPort repeater circuit of claim 9 , wherein training the one or more communication links on the upstream data interface and the one or more communication links on the downstream data interface includes:
determining a DPCD register-space revision level, a link rate, a lane count, a max downspread, a training Aux Rd interval, and Fast-Aux capability of the DisplayPort repeater circuit; and
determining a DPCD register-space revision level, a link rate, a lane count, a max downspread, a training Aux Rd interval, and Fast-Aux capability of the downstream device.
11. The DisplayPort repeater circuit of claim 1 , wherein the second list of DPCP access transactions includes DisplayPort Native Aux transactions to DPCD registers reserved for messaging.
12. The DisplayPort repeater of claim 1 , wherein the second list of DPCD access transactions includes transactions to DPCD registers reserved for payload-bandwidth allocation related transactions and transactions to DPCD registers reserved for messaging.
13. The DisplayPort repeater of claim 1 , wherein the second list of DPCD access transactions includes transactions to DPCD registers reserved for power management related transactions and transactions to DPCD registers reserved for messaging.
14. The DisplayPort repeater circuit of claim 13 , wherein the control circuit is further configured to, in response to a power management transaction received from the upstream data interface, adjust a power management setting of the DisplayPort repeater circuit and update one or more of the plurality of DPCD registers.
15. The DisplayPort repeater circuit of claim 1 , wherein the DisplayPort repeater is not assigned a global unique identifier.
16. A method of operating a DisplayPort repeater circuit, the method comprising:
determining a link configuration supported by both the repeater circuit and a downstream device coupled to the repeater circuit;
configuring an upstream link between the repeater circuit and an upstream device coupled to the repeater circuit, the configured upstream link providing the determined link configuration supported by both the repeater circuit and the downstream device;
configuring a link between the repeater circuit and the downstream device, the configured downstream and upstream links being symmetrical;
in response to receiving a DisplayPort configuration data (DPCD) access transaction from the upstream link, which requests access to a DPCD register included in a first list of DPCD registers, processing the DPCD access transaction by accessing one or more of a plurality of DPCD registers included in the repeater circuit; and
in response to receiving a DPCD access transaction from the upstream link, which requests access to a DPCD register included in a second list of DPCD registers, processing the DisplayPort access transaction by providing a transparent communication path to the downstream link for the DPCD access transaction.
17. The method of claim 16 , wherein configuring the upstream link and downstream link includes processing DPCD access transactions received from the upstream data interface, which are included in a list of link-training transactions, by accessing one or more of the plurality of DPCD registers included in the repeater circuit, the method further comprising:
after the configuration of the upstream and downstream links and in response to receiving a DPCD access transaction, which is included in the list of link-training transactions, from the upstream link, processing the DPCD access transactions by providing a transparent communication path to the downstream link for the transactions.
18. The method of claim 16 , wherein configuring the upstream and downstream links includes setting the upstream and downstream links to the same data rate.
19. The method of claim 17 , wherein one or more DPCD registers are included in both the first list of DPCD registers and the second list of DPCD registers.
20. The method of claim 16 , wherein the determining the link configuration supported by both the repeater circuit and a downstream device coupled to the repeater circuit includes:
determining a DPCD register-space revision level, a link rate, a lane count, a max downspread, a training Aux Rd interval, and Fast-Aux capability of the repeater circuit; and
determining a DPCD register-space revision level, a link rate, a lane count, a max downspread, a training Aux Rd interval, and Fast-Aux capability of the downstream device.
21. An article of manufacture, comprising, a processor-readable storage medium configured with configuration data that when executed by a processing integrated circuit (IC), cause the processing IC to operate as a repeater control circuit, the repeater control circuit configured to perform the steps including:
determining a link configuration supported by both the repeater circuit and a downstream device coupled to the repeater circuit;
configuring a link between the repeater circuit and an upstream device coupled to the repeater circuit, the configured upstream link providing the determined link configuration supported by both the repeater circuit and the downstream device;
configuring a link between the repeater circuit and the downstream device, the configured downstream and upstream links being symmetrical;
in response to receiving a DisplayPort configuration data (DPCD) access transaction from the upstream link, which requests access to a DPCD register included in a first list of DPCD registers, processing the DPCD access transaction by accessing one or more of a plurality of DPCD registers included in the repeater circuit; and
in response to receiving a DPCD access transaction from the upstream link, which requests access to a DPCD register included in a second list of DPCD registers, processing the DisplayPort access transaction by providing a transparent communication path to the downstream link for the DPCD access transaction.
22. The article of manufacture of claim 21 , wherein:
the configuring the upstream link and downstream link includes processing DPCD access transactions received from the upstream data interface, which are included in a list of link-training transactions, by accessing one or more of the plurality of DPCD registers included in the repeater circuit; and
the repeater control circuit is further configured to, following the configuration of the upstream and downstream links and in response to receiving a DPCD access transaction that is included in a list of link-training transactions, process the DPCD access transaction by providing a transparent communication path to the downstream link for the transaction.
23. A repeater circuit, comprising:
an upstream data interface;
a downstream data interface;
a plurality of configuration data registers, and
a control circuit coupled to the upstream data interface, downstream data interface and registers, the control circuit configured to:
operate in a link-configuration mode by processing register access transactions related to link training, received from the upstream data interface, using one or more of the plurality of registers to configure a link for communicating between an upstream device coupled to the upstream data interface and a downstream device coupled to the downstream data interface; and
for one or more register access transactions included in a first list of register access transactions, operate in a transparent-link-communication mode by providing a transparent communication path in the link between the upstream device coupled to the upstream data interface and the downstream device coupled to the sink data interface.
24. The repeater circuit of claim 23 , wherein the providing the transparent communication path involves forwarding register access transactions received from the upstream data interface to the downstream data interface.