AND IN eUSB2 REPEATER

BACKGROUND

[0001] This relates generally to reducing power consumption in USB 2.0 redrivers and in embedded USB 2.0 (eUSB2) repeaters.

[0002] Universal Serial Bus (USB) is an industry standard that establishes protocols for connection, communication and power supply for computers, peripheral devices and communication devices. The expansion of USB has resulted in the development of wide range of USB devices with varying power requirements. As power efficiency becomes critical in computers, peripheral devices and communication devices, embedded USB 2.0 (eUSB2) devices are used as a low voltage solution to traditional USB 2.0 devices.

[0003] To extend link distances and boost signal quality on a USB bus, USB 2.0 redrivers are used, while eUSB2 repeaters are used to convert signals between eUSB2 and USB 2.0. Generally, USB 2.0 redrivers and eUSB2 repeaters regenerate signals using equalizers and amplifiers to allow longer channel transmission and to reduce bit error rates. The bypassed signals are also conditioned to remove jitters.

[0004] According to a protocol, USB 2.0 redrivers and eUSB2 repeaters are required to repeat a high speed (HS) packet within 4 HS unit intervals (UIs) of receiving the packet. Also, the protocol requires that a peripheral device will only transmit to a host after receiving a packet from the host, and the peripheral device is required to transmit within 192 UIs of receiving a packet from the host. To comply with the protocol, transmitters generally operate in two states: an active state, and a standby state. In the active state, the transmitters transmit packets at full power by driving current to a load. In the standby state, although the transmitters remain idle, current is shunted to ground to maintain internal nodes and bias loops at normal levels to allow a quick transition to the active state. When the transmitters transition from the standby state to the active state, current is simply switched back to the load. As a result, power consumption in the standby state is same as the power consumption in the active state. Reduction in power consumption in USB 2.0 redrivers and in eUSB2 repeaters is desired. SUMMARY

[0005] Various aspects of this description are directed to methods for reducing power consumption in USB 2.0 redrivers and embedded USB 2.0 (eUSB2) repeaters.

[0006] In one aspect, a method includes detecting a micro start of frame packet (pSOF) on a data bus. The pSOF indicates the start of a microframe. The method further includes determining whether any data packet is contained in the microframe during a first threshold period after the pSOF. If at least one data packet is contained in the microframe during the first threshold period after the pSOF, one or more transmitters are held in an active state. If no data packet is contained in the microframe during the first threshold period after the pSOF, the transmitters are transitioned from the active state to an OFF state. The method also includes transitioning the transmitters from the OFF state to the active state prior to a switchback period before the end of the microframe. The method also includes transitioning the transmitters from the OFF state to the active state if a data packet is received in the OFF state. The method also includes receiving a data packet in the OFF state and dropping the data packet received in the OFF state. The method also includes transitioning the transmitters from the OFF state to the active state when the data packet is dropped.

[0007] In another aspect of this description, the method includes setting a timer with at least a first, a second, and a third expiration time, wherein the first expiration time is the length of the microframe, the second expiration time is the first threshold period, and the third expiration time is the switchback period. The method also includes operating the communication device using the timer.

[0008] In an additional aspect of this description, a method includes detecting a micro start of frame packet (pSOF) on a data bus. The method further includes determining whether any data packet is contained in the microframe during a first threshold period after the pSOF. If no data packet is contained in the microframe during the first threshold period after the pSOF, the transmitters are transitioned from the active state to an OFF state. If at least one data packet is contained in the microframe during the first threshold period after the pSOF, the transmitters are held in the active state for a second threshold period. The method also includes transitioning the transmitters from the OFF state to the active state if a data packet is received in the OFF state. The method also includes transitioning the transmitters from the OFF state to the active state prior to a switchback period before the end of the microframe. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a block diagram illustrating a peripheral device connected to a host.

[0010] FIG. 2 is a block diagram of an eUSB2 peripheral repeater.

[0011] FIGS. 3A-3D and 4A-4D show timing diagrams of packets and transmitter states according to embodiments.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0012] FIG. 1 is a block diagram 100 illustrating a peripheral device 104 connected to a host 106 in accordance with an example embodiment. The peripheral device 104 includes an eUSB2 peripheral repeater 108 connected to a peripheral system-on-chip (SoC) 112 via an eUSB2 bus 116. The peripheral SoC 112 can be a processor, a controller or the like.

[0013] With reference to FIG. 1, the host 106 includes a host repeater 120 interconnected with a host SoC 124 via an eUSB2 bus 128. The host 106 is connected to the peripheral device 104 via a USB 2.0 bus 132. Thus, the USB 2.0 bus is used as an external connection between the host 108 and the peripheral device, and the eUSB2 bus 116 is used for inter-chip interconnect (e.g., interconnect the eUSB2 peripheral repeater 108 and the peripheral SoC 112).

[0014] In operation, the host 106 transmits a downstream packet to the peripheral device 104 over the USB 2.0 bus 132. The peripheral repeater 108 converts the received downstream packet, which is in a USB 2.0 signal form, to a downstream signal in an eUSB2 signal form and sends the downstream packet to the peripheral SoC 112 over the eUSB2 bus 116. The peripheral SoC 112 may respond to the host with an upstream packet which is transmitted to the peripheral repeater 108 over the eUSB2 bus 116. The peripheral repeater 108 converts the upstream packet, which is in an eUSB2 signal form, to an upstream packet in a USB 2.0 signal form and transmits the upstream packet to the host 106 over the USB 2.0 bus 132. Thus, the peripheral repeater 108 converts a USB 2.0 signal to an enUSB2 signal and vice versa.

[0015] Although the example embodiments are described herein with reference to an eUSB2 repeater, this description is also applicable to a USB 2.0 redriver and to an eUSB2 redriver. The techniques described herein are useful to reduce power consumption of an eUSB2 repeater, a USB 2.0 redriver, and an eUSB2 redriver. This description is applicable to a repeater which may reside inside a peripheral device or inside a host device.

[0016] FIG. 2 is a more detailed block diagram of the eUSB2 peripheral repeater 108 in accordance with an example embodiment. The eUSB2 peripheral repeater 108 includes a USB 2.0 port 204 configured to interface with a USB 2.0 bus 208. The USB 2.0 bus 208 provides connection to an external device such as the host 106 (shown in FIG. 1). The USB 2.0 port 204 includes a USB transmitter 212 and a USB receiver 216. The eUSB2 peripheral repeater 108 receives a downstream packet from a host over the USB 2.0 bus 208 through the USB receiver 216 and transmits an upstream packet to the host over the USB 2.0 bus 208 through the USB transmitter 212.

[0017] With continuing reference to FIG. 2, the eUSB2 peripheral repeater 108 also includes an eUSB2 port 220 configured to interface with an eUSB2 bus 224. The eUSB2 bus 224 provides an inter-chip interconnect with the peripheral SoC 112 (shown in FIG. 1). The eUSB2 port 224 includes an eUSB2 transmitter 228 and an eUSB2 receiver 232. The eUSB2 peripheral repeater 108 receives an upstream packet from the peripheral SoC 112 or another device over the eUSB2 bus 224 through the eUSB2 receiver 232 and transmits downstream packet to the peripheral SoC 112 (shown in FIG. 1) or another device over the eUSB2 bus 224 through the eUSB2 transmitter 228.

[0018] In one aspect, a micro start of frame packet (pSOF) is used to calibrate the eUSB2 repeater 108 (or a USB 2.0 redriver). The pSOF indicates the start of a microframe which has a length of 125 ps. The pSOF is periodically broadcast on the USB 2.0 bus 208 every 125 ps.

[0019] In an example embodiment, the pSOF is detected on a data bus (e.g., the USB 2.0 bus 208 or the eUSB2 bus 224) and a timer is set with multiple threshold periods that are used to control (i.e., disable and enable) one or more transmitters. Depending on the type of devices used in a connection, various transmitter combinations are possible: USB 2.0 and USB 2.0; eUSB2 and eUSB2; and eUSB2 and USB 2.0. In these combinations, one or both transmitters can be controlled. In an example embodiment, one or both of the 2 USB 2.0 transmitters can be controlled. In another example embodiment, one or both of the 2 eUSB2 transmitters can be controlled. In yet another example embodiment, one of both of eUSB2 transmitter or USB 2.0 transmitter can be controlled.

[0020] In an example embodiment, a squelch circuit (not shown in FIG. 2) can be used to detect the pSOF. By locking onto the pSOF and turning OFF (i.e., disabling) one or both of the eUSB2 and USB 2.0 transmitters 228, 212 when the USB 2.0 bus 208 is idle, power consumption is reduced.

[0021] In an example embodiment, the eUSB2 repeater 108 repeats isochronous packets (ie., time critical data) and asynchronous packets (i.e., bulk data) by relying on the multiple threshold periods while reducing power consumption. Because isochronous packets are bundled at the beginning of a microframe, one or both of the transmitters 212, 228 are turned OFF after isochronous data is transmitted. By holding the transmitters 212, 228 in an active state at the beginning of the microframe and by selecting a turn OFF threshold greater than normal inter packet gaps, isochronous packets are transmitted. The transmitters 212, 228 are disabled during an idle portion of the microframe and are re-enabled before the next pSOF.

[0022] In an example embodiment, if asynchronous packets arrive late in the microframe after the transmitters 212, 228 are disabled, the asynchronous packets are dropped. However, because a host must support retries of dropped asynchronous packets, the transmitters 212, 228 are re-enabled to an active state and held in the active state for the next 8 microframes to allow for the maximum retry times.

[0023] Immediately before the arrival of the pSOF, the transmitters 212, 228 are in an active state. When the pSOF is detected on the bus (e.g., USB 2.0 bus 208), a determination is made about whether any data packet is contained in the microframe during a first threshold period after the pSOF. The first threshold period may be set as a percentage of the length of the microframe. In an example embodiment, the first threshold period may be 31.25 ps. The first threshold period is also referred to as T OFF period and may, for example, be 31.25 ps. In another example embodiment, the first threshold is updated after a pSOF is received for continuous calibration.

[0024] If at least one data packet is contained in the microframe during the first threshold period after the pSOF, the transmitters 212, 228 are held in the active state to allow the transmitters 212, 228 to transmit the data packet. However, if no data packet is contained in the microframe during the first threshold period after the pSOF, the transmitters 212, 228 are transitioned from the active state to an OFF state. In the OFF state, the transmitters 212, 228 are disabled. The transmiters 212, 228 are held in the OFF state until prior to a switchback period before the end of the microframe. The transmitters 212, 228 are transitioned from the OFF state to the active state prior to the switchback period before the end of the microframe to ensure that the transmitters 212, 228 are ready for the next microframe. The switchback period is greater than the maximum time required for transmitter to transition to the active state. However, if a data packet is received at any time during the OFF state, the transmitters 212, 228 are transitioned from the OFF state to the active state. [0025] If a data packet arrives when the transmitters are in the OFF state, the data packet is dropped. However, the transmitters 212, 228 are transitioned from the OFF state to the active state if a data packet is dropped. Because the dropped data packet is retried, the transmitters 212, 228 are transitioned to the active state to transmit when the data packet is retried.

[0026] When a data packet arrives while the transmitters 212, 228 are disabled, the transmitters 212, 228 are enabled following a normal sequence. Because it requires 1.4 ps to fully re-enable repeating, additional data packets received during this time is dropped. In an example embodiment, if a data packet is dropped the transmitters 212, 228 are transitioned to the active state and is held in the active state for the next 8 microframes.

[0027] Variations within the scope of this description are possible. In an example embodiment, immediately before the arrival of the pSOF, the transmitters 212, 228 can be in a standby state instead of being in the active state. In the standby state, current is shunted to ground instead of being driven to a load. The transmitters 212, 228 are transitioned from the standby state to the active state to transmit data packets.

[0028] Although the transmitter remains idle in the standby state, current is shunted to ground to maintain internal nodes and bias loops at normal levels to allow a quick transition to the active state. When the transmitter transitions from the standby state to the active state, current is simply switched back to the load. As a result, the power consumption by the transmitter in the standby state is approximately equal to the power consumption in the active state.

[0029] FIGS. 3A-3D illustrate timing diagrams of various packet structures on the USB 2.0 bus 208 and various states of the transmitter in accordance with an example embodiment. The transmitter can, for example, be the USB 2.0 transmitter 212 or the eUSB2 transmitter 228.

[0030] With reference to FIG. 3A, initially the transmitter is in an active state and a pSOF is detected on the USB 2.0 bus 208. The transmitter is held in the active state during the first threshold period after the pSOF. Because no data packet exists during the first threshold period, the transmitter is transitioned from the active state to an OFF state. The transmitter is transitioned from the OFF state to the active state prior to the switchback period before the end of the microframe to prepare for the arrival of the next pSOF. The switchback period is greater than the maximum time required for the transmitter to transition to the active state.

[0031] With reference to FIG. 3B, several data packets are contained in the microframe during the first threshold period after the pSOF. Accordingly, the transmitter is held in the active state to allow the transmitter to transmit the data packets. In this scenario, the transmitter is not disabled during the entire microframe.

[0032] With reference to FIG. 3C, several data packets are contained in the microframe during the first threshold period after the pSOF. Accordingly, the transmitter is held in the active state. After the data packets are received during the first threshold period, the USB 2.0 bus 208 remains idle for some time until a late packet arrives. The late packet is a retry packet which is processed and transmitted by the transmitter. In this scenario, the transmitter is not disabled during the entire microframe.

[0033] With reference to FIG. 3D, no data packet exists during the first threshold period. Accordingly, the transmitter is transitioned from the active state to the OFF state after the first threshold period. However, a late packet arrives in the microframe while the transmitter is in the OFF state. Because the late packet is received in the OFF state, the late packet is dropped and the transmitter is transitioned from the OFF state to the active state. A retry packet is received, and the retry packet is successfully repeated. Thus, the transmitter is re-enabled if a packet is received while the transmitter is disabled. In an example embodiment, if a packet is dropped, the transmitter is transitioned to the active state and is held in the active state for the next 8 microframes to allow for the maximum retry times.

[0034] In another example embodiment, if no data packet is contained in the microframe during the first threshold period after the pSOF, the transmitter is transitioned from the active state to an OFF state. However, if at least one data packet is contained in the microframe during the first threshold period after the pSOF, the transmitter is held in the active state for a second threshold period. After the second threshold period, the transmitter is allowed to transition from the active state to the OFF state. The transmitter is again transitioned from the OFF state to the active state prior to a switchback period before the end of the microframe. If, a data packet is received during the OFF state, the data packet is dropped, and thereafter the transmitter is transitioned from the OFF state to the active state to be ready to transmit the retried packet. In an example embodiment, the length of the second threshold period is twice the length of the first threshold period.

[0035] FIGS. 4A-4D illustrate timing diagrams of various packet structures on the USB 2.0 bus 208 and various states of the transmitter in accordance with an example embodiment. The transmitter can, for example, be the USB 2.0 transmitter 212 or the eUSB2 transmitter 228. [0036] With reference to FIG. 4A, initially the transmitter is in an active state and a pSOF is detected on the USB 2.0 bus 208. The transmitter is held in the active state for the first threshold period after the pSOF. Because no data packet exists during the first threshold period, the transmitter is transitioned from the active state to an OFF state after the first threshold period. The transmitter is transitioned from the OFF state to the active state prior to the switchback period before the end of the microframe for the arrival of the next pSOF. The switchback period is greater than the maximum time required for the transmitter to transition to the active state.

[0037] With reference to FIG. 4B, several data packets are contained in the microframe during the first threshold period after the pSOF. Accordingly, the transmitter is held in the active state to allow the transmitter to transmit the data packets. However, if no new data packet is received in a second threshold period, the transmitter is transitioned from the active state to the OFF state. The transmitter is again transitioned from the OFF state to the active state prior to the switchback period before the end of the microframe. In this scenario the transmitter is held in an active state because several data packets are received in the first threshold period. To reduce power consumption, if no new data packet is received in a second threshold period, the transmitter is allowed to transition from the active state to the OFF state.

[0038] With reference to FIG. 4C, several data packets are contained in the microframe during the first threshold period after the pSOF. Accordingly, the transmitter is held in the active state to allow the transmitter to transmit the data packets. Similar to the scenario in FIG. 4B, no new data packet is received in the second threshold period. Thus, to reduce power consumption, the transmitter is allowed to transition from the active state to the OFF state after the second threshold period. After the second threshold period, the transmitter is transitioned from the active state to the OFF state. After the transmitter is disabled, a late packet arrives which is dropped. Thus, the transmitter is transitioned from the OFF state to the active state to transmit the retried the packet.

[0039] With reference to FIG. 4D, no data packet is contained in the microframe during the first threshold period after the pSOF. Thus, the transmitter is transitioned from the active state to the OFF state after the first threshold period. A late packet which arrives while the transmitter is in the OFF state is dropped. The transmitter is transitioned from the OFF state to the active state to transmit the retried packet. The retried packet is successfully repeated.

[0040] While use of two threshold period results in greater power efficiency than use of only a single threshold period, use of two threshold periods also increases risk of system errors.

[0041] Various illustrative components, blocks, modules, circuits, and steps are described herein in general terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0042] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.