thedark
Second Lieutenant
Joined: 30 Jul 2005
Posts: 1074
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 Posted: Thu Aug 04, 2005 5:36 pm Post subject: Bus Master Direct Memory Access (e.g. LANCE, DEC 21040) |
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Pro: Frees up the CPU during the data transfer, can string together buffers, can require little or no CPU time lost on the ISA bus. Most of the bus-mastering linux drivers now use a `copybreak' scheme where large packets are put directly into a kernel networking buffer by the card, and small packets are copied by the CPU which primes the cache for subsequent processing.
Con: (Only applicable to ISA bus cards) Requires low-memory buffers and a DMA channel for cards. Any bus-master will have problems with other bus-masters that are bus-hogs, such as some primitive SCSI adaptors. A few badly-designed motherboard chipsets have problems with bus-masters. And a reason for not using any type of DMA device is using a 486 processor designed for plug-in replacement of a 386: these processors |
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