Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output data buffering
Reexamination Certificate
1997-05-01
2001-02-06
Lee, Thomas C. (Department: 2782)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output data buffering
C710S112000, C710S120000, C370S402000
Reexamination Certificate
active
06185641
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a peripheral microcontroller for providing a high performance USB (Universal Serial Bus) connection to existing peripheral architectures (such as printers and disk drives with existing microcontrollers) and to new peripheral architectures (such as a 4-port USB-to-Ethernet Bridge).
The USB peripheral microcontroller includes three units. A Serial Interface Engine (SIE) connects to a USB host or USB hub. A Microcontroller (MCU) Interface Unit connects to one or more peripheral devices such as ISA-like peripherals. A Memory Management Unit (MMU) provides a buffering mechanism between the SIE and MCU Interface Unit.
The MMU utilizes a unique data packet buffering architecture. Packets received at the MMU from a peripheral for transmission to the USB host and packets received at the MMU from the USB host for transmission to a peripheral are buffered in a RAM. The capacity of the RAM is dynamically allocatable among various USB endpoints and the USB host so that the size of the RAM is minimized.
The data path of the inventive USB peripheral controller is also highly advantageous. The SIE accesses the packet buffer RAM via a DMA controller in the MMU. The MCU Interface Unit accesses the packet buffer RAM via a microcontroller or a DMA controller. An arbiter in the MMU enables these multiple masters to access the packet buffer RAM.
BACKGROUND OF THE INVENTION
The USB (Universal Serial Bus) is a peripheral bus specification developed by PC and telecom industry leaders. The USB brings the plug-and-play capability of computer peripherals outside the PC box. This eliminates the need to install cards into dedicated computer slots and reconfigure the system each time a peripheral is attached or detached from a PC. Personal computers equipped with USB allow computer peripherals to be automatically configured as soon as they are physically attached without the need to reboot or run setup. USB allows multiple devices—up to 127—to run simultaneously on a computer, with peripherals such as monitors and key boards acting as additional plug-in sites or hubs.
The USB is described in detail in the Universal Serial Bus Specification, Revision 1.0 published Jul. 15, 1996. The specification is jointly published by Compaq, Digital Equipment Corporation, IBM PC Company, Intel, Microsoft, NEC and Northern Telecom. The contents of this USB specification are incorporated herein by reference.
The USB bus topology may be described as follows. The USB connects USB devices with a USB host. There are two types of USB devices: the hub and the function. A hub is a device which provides additional attachment points for the USB. A function provides capabilities to the system, e.g., an ISDN connection, a digital joystick, a speaker, a keyboard, a mouse, etc. The hub and the function are described in greater detail below.
The USB physical interconnect is a tiered star topology. A hub is at the center of each star. Each wire segment is a point-to-point connection: (a) between the host and a hub, or (b) between a host and a function, or (c) between a hub and another hub or function.
FIG. 1
illustrates the topology of the USB system. The USB system
10
comprises a host
12
. There are two points of attachment in the host
12
: port
1
and port
2
. The port
2
is connected by the wire segment
28
to the function
29
. The port
1
is connected by the wire segment
18
to hub
1
. The hub
1
has five ports
20
. The function
22
is connected to one of these ports by the wire segment
24
. Similarly, the hub
2
and hub
3
are also connected to ports of hub
1
. Various functions (e.g., function
30
,
32
, etc.) are connected to ports on the hub
2
or the hub
3
.
Hubs are a key element in the plug-and-play architecture of USB. Hubs serve to simplify USB connectivity from the user's perspective and provide robustness at low cost and complexity. Hubs are wiring concentrators and enable the multiple attachment characteristics of USB. Attachment points are referred to as ports (see FIG.
1
). Each hub converts a single attachment point into multiple attachment points. The architecture supports concatenation of multiple hubs. The upstream port of a hub connects the hub towards the host. Each of the other downstream ports of a hub allows connection to another hub or function. Hubs can detect the attachment and detachment of a USB device at each downstream port and enable the distribution of power to these downstream USB devices. Each downstream port can be individually enabled and configured as either full or low speed. The hub isolates low speed ports from full speed signaling.
A function is a USB device that is able to transmit or receive data or control information over the USB. A function is typically implemented as a separate peripheral device with a cable that plugs into a port on a hub. However, a physical package may implement multiple functions and an embedded hub with a single USB cable. This is known as a compound device. A compound device appears to the host as a hub with one or more permanently attached USB devices. Examples of functions include a printer, a monitor, a mouse, a keyboard, a modem, an audio CD player, a tape player, an ISDN connection, etc.
There is only one host on any USB system. The USB interface to the host computer system is referred to as the host controller. The host controller may be implemented in a combination of hardware, firmware, or software. A root hub is integrated within the host system to provide one or more attachment points.
A device endpoint refers to a uniquely identifiable portion of a USB device (hub or function) that is a source or sink of information in a communication flow between host and USB device. An example of a USB function with more than one endpoint is a Data/Voice modem. There may be one endpoint for voice packets and one endpoint for data packets.
All bus transactions involve the transmission of up to three packets. Each transaction begins when the host controller, on a scheduled basis, sends a USB packet describing the type and direction of transaction, the USB device address, and endpoint number. This packet is referred to as the Token Packet. The USB device that is addressed by the Token Packet selects itself by decoding the appropriate address fields of the Token Packet. In a given transaction, data is transferred either from the host to a device or from a device to the host. The direction of data transfer is specified in the Token Packet. The source of the transaction then sends a data packet indicating whether the transfer was successful.
In general, most peripherals include I/O controllers which are designed to generate transactions for commonly used busses such as ISA, EISA, PCI, and the proprietary NU bus of Apple. It is desirable to adapt these peripherals for use with the highly advantageous USB. To accomplish this, it is desirable to provide a USB microcontroller which can generate familiar bus transactions such as ISA bus transactions from the USB serial protocol stream.
A block diagram of such a USB microcontroller unit is shown in FIG.
2
. This microcontroller unit
50
comprises three blocks, a USB Serial Interface Engine (SIE)
60
, Microcontroller Interface Unit
70
, and a Memory Management Unit (MMU)
80
. The SIE
60
connects to a port on a USB hub or on a USB host and serves as an interface to the USB protocol. Specifically, the SIE
60
formats data to be transmitted from the peripheral to the host in accordance with the USB protocol. It reformats data received from the USB host in accordance with the USB protocol into a form that can be buffered in the Memory Management Unit. The Microcontroller Interface Unit
70
interfaces with the I/O controller of the peripheral.
In conventional USB peripheral microcontrollers, the Memory Management Unit includes a plurality of FIFOs for buffering data packets, there being a dedicated FIFO for each USB endpoint.
Prior art USB microcontrollers are the 82930 Universal Serial Bus Microcontroller—available from Intel, USB Function Cor
Elamin Abdelmoniem
Lee Thomas C.
Proskauer Rose LLP
Standard Microsystems Corp.
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