Bus Interface ISA (Industry Standard Architecture) VESA local bus (Video Electronics Standards Association) PCI (peripheral component interconnect) USB (Universal Serial Bus) AGP (Advanced Graphics Port)

Slide Objectives Detail pin connections and signal connections on the ISA, VESA local, and PCI buses. Develop simple interfaces to the ISA, VESA local and PCI buses. Program interface places on boards that connect to the ISA, VESA local, and PCI buses. Describe operation of the USB and develop some short programs that transfer data. Explain how the AGP increases the efficiency of the graphics subsystem.

ISA Been around since the start of the IBM PC (1982) Originally an 8-bit standard, now 16-bit. There was a 32-bit EISA (Extended), gone Most PCs have an ISA slot on the mainboard that can accept either an 8-bit of a 16-bit ISA printed circuit card. 32-bit printer circuit cards are more often PCI, or in some older 486s, the VESA cards.

ISA / EISA / VESA local Clocking speed 8 MHZ too slow!! EISA -32-bit modification of ISA (386-PentiumII had 32-bit data buses) Both ISA and EISA run at 8 MHz too SLOW! VESA and PCI both run at 33 MHz. Most common application for EISA bus is as a disk controller or as a video graphics adapter. Both apps benefit from the wider bus width because the data transfer rates for these devices are high.

VESA local Much better approach to 32-bit interfacing Common for video and disk interfaces to the 486 PC

PCI PCI -Peripheral Component Interconnect Only bus found in the newest Pentium II systems. (Most systems also have ISA, but as an interface for older 8-bit and 16-bit interface cards). Has replaced VESA bus. Has plug and play(PnP) characteristics Has the ability to function with a 64-bit data bus. Most often used for interfacing I/O components Memory could be interfaced, but would operate only at a 33MHz rate with Pentium (half the speed of the redient local bus of the Pentium)

Plug and Play PCI interface contains a series of registers, located in a small memory device on the PCI interface, that contain information about the board. This memory can provide PnP characteristics to the ISA bus or any other bus. Information in registers allows computer to automatically configure the PCI card.

Bus Structure of the Pentium II   Pentium II Processor Local Bus 66MHz or 100Mhz AGP Video AGP Bus 66MHz 440LX or 440BX Chip Set Memory PCI Bus 33MHz or 66 MHz Local Frame Buffer PIIX4 Bridge I/O USB Bus 12Mbps ISA Bus 8 MHz Bus Structure of the Pentium II

PCI Bridge Not just buffers between PCI and processor busses. INTELLIGENT! Capable of grouping single data requests into bursts and then exchanging those bursts with memory and I/O devices. Ability to transfer an unlimited number of bytes in a single burst – even though processor itself may be limited to a much smaller size (one cache line) Each PCI device has a latency timer that defines longest time that device is allowed to control the bus.

PCI Bus Operation The data bus lines use a multiplexing scheme to which connector pins are multiplexed as address and data pins. A PIC transaction takes place between a master (a device takes control of the system buses), and a target (a device that only responds to access requests).

BUS Access Read cycle takes three clock pulses Write cycle Output address Switch lines from address to data Transfer data Write cycle Address lines do not have to turned around Only requires two clock cycles.

Bus Commands 16 different commands (commands are multiplexed on the C/BE3’-C/BE0’) lines and output during the address phase of each bus cycle. INTA sequence I/O read access I/O write access Memory read access Memory write access Dual addressing cycle (64 bits on 32-bit data bus) Line memory read access (line of cache (greater than 32 bits)

DMA and interrupts Bus Master concept of PCI eliminates necessity for DMA controller (still used) Bus master shuts down system board buses and communicates with adapters via bus slots.

PCI Adapters Support 3.3V, 5 V and Universal Separate slot arrangements for 3.3 and 5v. Universal adapters can work in either slot Each PCI card contains a 256-byte configuration memory. 64 bytes header (type of card, manufacturer, revision level, current status of card, cache line size in 32-byte units, and bus latency). Remaining bytes are card specific.

Plug and Play Configuration memory of units on PCI bus allow system to scan through devices and assign each device a unique base address and interrupt level.

I/O Buses SCSI (Small Computer Systems Interface) Parallel bus used to peripheral such as hard drives, tape drives, CD_ROM players. 1 to 10MB/sec (PCI around 275MB/sec transfer rate) Intelligent bus Accepts high level commands from processor and then transfer information without host participation. Allows parallel processing

SCSI Can accomodate 16 devices(SCSI-3) Must have host adapter (typically no.7) Devices connected in a daisy chain fashion with terminating plugs connected to each end of cable.

USB (Universal Serial Bus) Current ISA sound cards use internal PC power supply (generates a large amount of noise). USB allows sound cards to have their own power supply Easy to connect Access to up to 127 different connections through a 4 connection serial cable. Apps: keyboards, sound cards, simple video-retrieval devices, modems. Data transfer rates are 12Mbps full speed, 1.5 Mbps slow speed operation.

Physical Topology is point-to-point tree.

Root: primary controller Hub: allows the connection of multiple USB devices Endpoint: Source or sink of information within a USB device A USB device that contains an ENDPOINT (source/sink of data) is called a ‘function’. A USB device can be just a function, just a hub, or both a hub and a function.

Physical connection is point to point.

Pipes When attaching to a hub, host assigns a device an address. Characteristics of connection make up pipe Speed Direction Required bandwidth Error-handling capability Transfer type Maximum packet size The endpoint of the device communicates with the host. (endpoint 0 is for device initialization and configuration)

Bus Protocol Data transferred in packets Synchronous serial format Clock signal is encoded into data pattern Packets are variable length Includes: Sync field, packet id, Information field, and CRC

Data transfers Control Bulk (Text data for printer) Interrupt (mouse clicks) Isochronous (voice, music)

USB Connector 4 pins Biphase signals 5 v -Data +Data Ground When +data are at 5.0V, -data are at zero volts and vice versa

Physical Interface Differential Signaling, Half duplex Full Duplex: data transmission can occur in both directions at the same time Half Duplex: data transmission can go in only one direction at a time

USB Data Biphase signals generated using a differential line driver (transceiver) with noise suppression Uses NRZI encoding (non-return to zero, inverted) for transmitting packets. Signal level does not change for transmission of logic 1s Signal level is inverted for every change to a logic 0 Uses bit-stuffing for synchronization A logic 0 is added after 6 continuous 1s in a row Data is transmitted LSB to MSB.

USB Commands Stop and Wait Flow control used host must wait for ACK, NAK before transferring additional data packets Sync (80h), PID sent first 4 Types of Packets (Data, token, handshaking, and start-of-frame) 2 types of CRC used (5-bit and 16-bit) ACK, NAK tokens used to coordinate transfer of packets.

PID Codes PID Name Type Description E1h OUT Token Host->function transaction D2h ACK Handshake Receiver accepts packet C3h Data0 Data Data packet PID even A5h SOF Start of frame 69h IN Function -> host transaction 5Ah NAK Receiver does not receive packet 4Bh Data1 Data packet PID odd 3Ch PRE Special Host preamble 2Dh Setup Setup command 1Eh Stall Stalled

Types of Packets on USB Token 8 bits 7 bits 4 bits 5 bits PID ADDR   8 bits 7 bits 4 bits 5 bits PID ADDR ENDP CRC5 Start of Frame Packet 11 bits Frame Number Data Packet 1 - 1023 bits 16 bits Data CRC16 Handshake Packet

Accelerated Graphics Port Designed specifically to all high-speed transfers between video card frame buffer and system memory. Operates at bus clock frequency of the microprocessor. Maximum data transfer is 528MBps(2X) Max data rate for 4x system is 1GBps PCI bus has max data rate of 100MBps