USB isochronous transfer over a non-USB network
Methods and systems for synchronizing USB 2.0 isochronous IN and OUT transfer clocks over a non-USB network. One method for synchronizing isochronous IN transfer clocks includes: receiving, by a USB host adaptor (USBH), packets from a USB host; writing in each packet an indication of the time in which the packet was received by the USBH; sending the packets from the USBH to a USB device adaptor (USBD) over the network; and synchronizing the USBD clock to the USBH clock based on a property related to the received packets.
1. A method for synchronizing Universal Serial Bus (USB) 2.0 isochronous OUT transfer clocks over a network, comprising:
receiving, by a USB host adaptor (USBH), packets from a USB host;
for at least 1% of the packets:
writing in each packet, by the USBH, an indication of the time in which the packet was received by the USBH;
sending the packets from the USBH to a USB device adaptor (USBD) over the network; and
synchronizing a USBD clock to a USBH clock based on a property related to the packets.
2. The method of claim 1 , wherein the indication of the time in which the packet was received by the USBH is implemented by writing in the packet the number of the Microframe in which the packet was received by the USBH.
3. The method of claim 1 , wherein the indication of the time in which the packet was received by the USBH is implemented by writing in the packet the number of the Microframe in which the packet was received by the USBH; and the USBH is writing in each packet, sent from the USB host to the USBH, the number of the USB Microframe in which the packet was received by the USBH.
4. The method of claim 1 , wherein the property related to the packets is the status of the USBD FIFO buffer, and the USBD is synchronizing its clock to the USBH clock based on the status of the USBD FIFO buffer.
5. The method of claim 4 , wherein when the USBD FIFO buffer does not have enough packets to transmit to the USB device connected to it, the USBD slows down its clock.
6. The method of claim 1 , wherein the property related to the packets is the time difference between receiving and forwarding the packets.
7. The method of claim 6 , wherein the USBD is synchronizing its clock to the USBH clock by ensuring a constant time difference between receiving a certain packet at the USBH and forwarding the certain packet from the USBD FIFO to the USB device.
8. The method of claim 1 , wherein the network is an HDBaseT™ network.
9. A non-USB network configured to support Universal Serial Bus (USB) 2.0 isochronous OUT transfers, comprising:
a USB host adaptor (USBH) configured to receive packets from a USB host;
for at least 1% of the packets, the USBH is further configured to: write in each packet an indication of the time in which the packet was received by the USBH, and send the packets to a USB device adaptor (USBD) over the network; and
the USBD is configured to synchronize a USBD clock to a USBH clock based on a property related to the packets.
10. The non-USB network of claim 9 , wherein the indication of the time in which the packet was received by the USBH is implemented by writing in the packet the number of the Microframe in which the packet was received by the USBH; and the USBH is further configured to write in each packet, sent from the USB host to the USBH, the number of the USB Microframe in which the packet was received by the USBH.
11. The non-USB network of claim 9 , wherein the property related to the packets is the status of the USBD FIFO buffer, and the USBD is further configured to synchronize its clock to the USBH clock based on the status of the USBD FIFO buffer.
12. The non-USB network of claim 11 , wherein when the USBD FIFO buffer does not have enough packets to transmit to the USB device connected to it, the USBD is further configured to slow down its clock.
13. The non-USB network of claim 9 , wherein the network is an HDBaseT™ network.
14. A method for synchronizing Universal Serial Bus (USB) 2.0 isochronous IN transfer clocks over a network, comprising:
receiving, by a USB device adaptor (USBD), packets from a USB device;
sending the packets from the USBD to a USB host adaptor (USBH) over the network;
sending a representation of a USBH clock to the USBD; and
controlling the communication rate of the isochronous IN transfer by adjusting the representation of the USBH clock based on a property related to the packets that were received by the USBH from the USBD.
15. The method of claim 14 , wherein the USBH is slowing down the clock by less than 2%.
16. The method of claim 14 , wherein the USBH is increasing the clock by less than 2%.