USB The topics covered in order are USB
USB The topics covered, in order, are • USB background • Is USB the right solution? • Hardware issues • Software issues
A Quick USB Background • Three data rates are supported – low speed (1. 5 Mbit/sec), full speed (12 Mbit/sec), and high speed (480 Mbit/sec) • One host, many peripherals. The host controls all USB operations-sending data to and requesting data and status. • The USB cabling can carry power as well as data • Data transfer • • Bulk Transfers Control Transfers Isochronous Transfers Interrupt transfers • Hot pluggability, no pre-configuration – USB OTG
Is USB The Right Solution? • Host or peripheral application needs to adhere to one of the class standards. • OS and USB software
Can Your Hardware Support USB? • Bus Access: will need 8, 16, or 32 bits of address and data to connect a USB host controller. In order to move data efficiently, this memory space will need access times on the order of 50 -90 nanoseconds • System Throughput: Multiple host ports on one host controller will increase the load • Interrupt Load: Full-speed and low-speed USB have frame intervals of 1 ms, Highspeed USB uses a microframe interval of 125 microseconds • Memory: A robust USB stack may take 30 -100 KB of code storage, and 10100 KB of runtime memory. • PCB Footprint: Embedded USB host controllers are typically in 80 -128 pin packages
USB Software Needs • Operating systems that have a native USB stack –eg. Linux and Microsoft’s Win. CE • Operating systems that do not have a native USB stack - Third party vendors may provide stacks for some USB controllers • What if there is no operating system at all? • USB peripherals - only respond to commands from the host – no underlying OS support. • The USB host protocol – requires RTOS for enumerating a device, handling asynchronous events, generating command packets
Linux Boards- Comparison FOX Board VIPER Kernel Full Linux ver 2. 4. 31 Embedded Linux v 2. 6 Language C, C++, PHP, PYTHON Tools GNU C compiler Linux Boards PC/104 -compliant Software Features: Hardware Features: Data Transfer Rate Up to 64 Mbytes 64 MB SDRAM Ports USB 1. 1 (low speed & full speed ) 8 MB FLASH 32 MB RAM 2 USB 1. 1 Dual USB host ports v 1. 1 USB Host and USB Slave ports Power 5 Volt 280 m. A (1 watt) 1. 9 W @ + 5 V only Cpu Axis ETRAX 100 LX 32 bit, RISC, 100 MHz (100 MIPS) Two 40 pins sockets Memory pins sockets Other Interface 40 digital I/O lines I²C interface I 2 C/I 2 S bus
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