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Embedded Systems December 2000 Vol13_13

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TFS is certainly not the answer to all embedded system FFS problems, but it does a good job of providing a fairly lIseful alternative for pl'ojects that can't justify the use and/or purchase of an off-the-shelf FFS. ed by the deleted fil es is cleaned up and the current list of active fi les is placed end-to-end in the flash. This means that each sector u ed by TF must be copied to the spare ector. Then that sector is erased and only the active files in that sector are copied back to the original sector from the spare sector. This is repeated for each ector in TFS. The defragmentation attempts to make this as sector-erase- effi cient as poss ible. If a sector is not affected by ule defragmentation , then it is left untouched; hence, the num- ber of sectors actually affected by a defragme nta tion depends on th e amount of fl ash space currenuy being used by TF and the position of the delcted fil es within the flash space. In a typical em bedded system pro- ject, the files in TFS will be the appli- cation itself, a monrc fi Ie for system configuration followed by other appli- cation-specific files . The application executable i likely to be the largest fil e and also the least likely to change at a high frequency. This means that the space taken up by the application executable is fairly static. Hence, the number of sectors occupied by ule application will not contribute to the wear of the spare sector. This fact in and of itself increases the estimated life expectancy calculated previously. On the other hand, if the application executable is quite large relative to the LOtal TFS space available, and if there are any fi les that are to be modificd on Take it for a spin TFS is certai nly not the answer to all embedded system FFS problems, but it does a goodjob of providing a fairly use- [l.t! alternative for projects Ulat can't jus- tilY the use and/ or purchase of an ofI- the-shelf FFS. I il1\~te you to take a look at ule entire boot platform that uses TFS. Your feedback is welcome. It pro- vides an embedded system wiUl TFTP and XMODEM, boul of which are inte- grated with TFS; hence, a field-upgrade capability. ASCII fil es can be edited on board wiul a simple line-mode fi le edi- tor. Fi les can be made executable scripts. There are capabilitie for appli- cation debug, memory test, modifica- tion , and so on, UDP command line interface option, DHCP / BOOTP and some ICMP. Check it out. esp Ed SuUer graduated from the engineering p' rogram at DeVry Technical institute, and received a bachelor's degree from New Jersey institute of Technology (NJTT). He is cur- rently a distinguished member of the t('ch- nical staff at Lucent T('chnologies. He has been writing code for embpcided s,)'stems at Lucent/AT&T Bell Labs for about 15 yean, for architectures ranging from the 8051 to MiPS R4000. His area of expertise includes embedded system bootup, device d' rivers, and RTOS BSP deveiojJ1nent, as well as Unix/Win32 based embedded sys- t!'T1I develojlment/ support tools. He can be rfached at l('suuer@Worldnet.aU.net. t~C/~rr~ยท WIREtESS For more information, contact us at info@zucoHo.com, or toll free at a77-Zucotto. References 1. TFS is part of a generic embedded sys- tem boot platform c;alled MicroMonitor (sometimes referred to as "the monitor" in this text) that Lucent Technologies is making available to outside developers. The source code for the entire platform is on Lucent's Software Solutions Group Web site (www./ucentssg.com) under the "Free Downloads" section. 88 DECEMBER 2000 Embedded Systems Programming a regular basis, defragmentation will be run more frequenuy. The point i that the actual wearing rate of the flash i application-specifi c and must be ul0ught out seriously.

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