Date: Thu, 16 Mar 1995 08:24:54 -0800 (PST) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: chitra@CS.SunySB.EDU (Chitra Venkatramani) Cc: hackers@FreeBSD.org Subject: Re: net question Message-ID: <199503161624.IAA15778@gndrsh.aac.dev.com> In-Reply-To: <199503161523.KAA21273@cs.sunysb.edu> from "Chitra Venkatramani" at Mar 16, 95 10:23:03 am
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> > > Hi! > In if_ed.c, the ethernet driver, the sizes of the transmit and > receive buffers are set. For 16bit cards, the transmit buffer size > is set to 2 buffers, each 6 pages, each page being 256 bytes. > And the remaining memory is set aside for the receiver ring buffer. > > I would like to know if it is possible to set the transmit buffer > size to be larger, say 6 buffers and leave the rest for the receiver, > in software ? That is, is this parameter software configurable ? There is no real reason to have more than 2 transmit buffers, it will just waste NIC memory. The NS8390 and dirived chips do not have chained trasmitter sections, they can only handle 1 transmit buffer at a time. The reason there are 2 buffers is so that you can have one active on the transmitter while you fill in the second one with data from the host, as soon as the active buffer completes transmission the buffers are swapped. Haveing more than 2 buffers would greatly complicate the buffer swapping code and probably end up makeing the driver slower (realize this driver can already transmit at FULL or near FULL ethernet speed using a 486DX33 and a 16 bit memory mapped card like the WD8013). -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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