Date: Sun, 01 Feb 2009 19:56:57 -0600 (CST) From: Sergey Babkin <babkin@verizon.net> To: bsd.quest@googlemail.com Cc: freebsd-hackers@freebsd.org Subject: Re: bus_dma (9). What exactly means "Loading of memory allocation" ? Message-ID: <6699015.16785.1233539817447.JavaMail.root@vms063.mailsrvcs.net>
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If I remember correctly, loading means that the pages become mapped and= visible to the devices. Some buses can access only a limited address space= , like ISA has only a 24-bit address. When a map gets loaded, for any pages= outside of this range the temporary in-ramge pages are allocated and the d= ata gets moved through them. On some machines, like I think DEC Alpha, the = physicall addresses seen by the devices are not the same as seen by the CPU= , these need to be translated. And so on. I think my real old articl= e had some of these explanations but now the Daemonnews site seems to be re= al slow: http://ezine.daemonnews.org/200008/isa.html -SB (sorry a= bout top quoting, it's the only kind the web interface of my provider suppo= rts) Feb 1, 2009 03:38:27 PM, [1]bsd.quest@googlemail.com = wrote: = Hi, at first the cut of text from man (9) bus_dma: bus_dmamap_t = A machine-dependent opaque type describing an individual mapp= ing. One map is used for each memory allocation that will b= e loaded. Maps can be reused once they have been unloaded..= . Question: What exactly means "Loading of memory allocation" in thi= s context ? Could anyone explain it or give me some little example wi= th DMA functions for understanding it. References 1. 3D"mailto:bsd.quest@googlemail=
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