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Peripherals Connecting

Fundamentals

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Peripherals Connecting

• Peripherals can be connected as:– Memory Mapped Devices (MMIO)– I/O bus (PMIO)

• Wired on PCB

• Externally wired

– I/O bus + Memory Mapped– Via an Interface

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Peripherals Connecting (cont)

• Memory Mapped Devices– Peripheral object work as an ore or

more memory address, readable, writeable or both.

– Peripheral can have an interrupt line (not mandatory)

– Programmers communicate with peripheral, writing or reading a particular memory address

– WARNING in some HW r/w operation can generate a fault interrupt, when attempting to do an illegal operation, such read on address for writing and viceversa; when this occur a system crash must be handled.

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Peripherals Connecting (cont)

• I/O bus (PMIO)– Some HW architectures have a

supplemental bus for I/O and instructions for reading & writing on this bus

– I/O process doesn’t interfere with cpu-memory exchanging

– Reading/Writing bus speeds can be different between memory and peripherals

• I/O bus + Memory Mapped– Both method, tipical device is the

Video Card on PC

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Peripherals Connecting (cont)

• On Board Interfaces– Bus Bridges

• Adapt a bus to another– Speed adjustment

– Electrical adjustment

– Electrical Insulating

– Limit interrupt rate to principal bus

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Peripherals Connecting (cont)

• On Board interfaces (cont)– Bus bridges (cont)

• Local Bus – Eisa– LAN– SCSI– PCI– USB

• Bus Bridged vs peripherals

– P2P wire (SATA disks)– Multiplexed wire

» IDE/EIDE» USB» ….

– PCB wired (PCI cards)

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Peripherals Connecting (cont)

• On Board interfaces (cont)– Bus bridged (cont)

• Generally are microprocessor controlled cards able to do complex I/O operation with simply interface commands

– Ex: LAN Cards receive destination MAC address and data buffer, then perform complete I/O:

» Carrier On» Test power on line» Collision:

Detected: random wait and retryNot detected: transmit msg one bit at timeVerify Transmitted:

OK->returnNOK & #retry>0 -> retransmit …

» ….

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Peripherals Connecting (cont)

• On Board interfaces (cont)– Directly Wired On PCB

– Wired outside PCB

– Most Common:• I2C

• SPI

• Ethernet

• USB

• RS232

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Peripherals Connecting (cont)

• Point to Point (P2P)– One physical

connection for device

• Multiplexed Devices (MUX)– One physical

connection for devices