©F.M. Rietti Peripherals Connecting Fundamentals

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 2 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

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 3 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.

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 4 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

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 5 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

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 6 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)

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 7 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 retry Not detected: transmit msg one bit at time Verify Transmitted: OK->return NOK & #retry>0 -> retransmit … »….

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 8 Peripherals Connecting (cont) On Board interfaces (cont) –Directly Wired On PCB –Wired outside PCB –Most Common: I2C SPI Ethernet USB RS232

©F.M. Rietti LM-18 Computer Science SSI Embedded Systems I 9 Peripherals Connecting (cont) Point to Point (P2P) –One physical connection for device Multiplexed Devices (MUX) –One physical connection for devices