speed of writing file is fixed when changing the CLK of SD/MMC
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From: bobo on 7 Feb 2010 16:52 >On Feb 7, 11:20=A0am, "bobo" <beyondsakai(a)n_o_s_p_a_m.126.com> wrote: >> >On Feb 5, 8:33=3DA0pm, "bobo" <beyondsa...(a)126.com> wrote: >> >> Hello All, >> >> =3DA0 =3DA0 I met a strange problem : >> >> =3DA0 =3DA0 the speed of writing file is fixed to a same value (about >> 50KB/s) >> >> whatever the SD/MMC CLK (from 600KHz to 12MHz), my platform is LPC2478= >, >> S=3D >> >D >> >> >Assuming your code actually does what you think it does, this suggests >> >that the time spent transferring data to/from the card over the serial >> >interface is buried in the time the card's controller requires for >> >erasing/rewriting data. >> >> Hi larwe, shall i erase pages before write it ? but the SD/MMC needn't th= >is >> operation, the controller int the SD/MMC card will do this automaticly, i= >f > >The card does it automatically, but it STILL TAKES FINITE TIME. > Hi, it's still slowly, I find that the erase a page also cost much time as write single page, and i tried to use sdmmc_write_pages() (for multiple page write) to write 1 page, it became fast, the speed up to 250~500KB/s, but it not stable enough, i write a test case to for it (just write page one by one and read ,compare, continuously) , after 300~500 times write, cmd12 timeout error occurs..., if i use sdmmc_write_pages() to write multiple pages, the timeout error occur more quickly... "The card does it automatically, but it STILL TAKES FINITE TIME.", don't you think the time is too long ? as i know, SD/MMC are similar to NAND, and the erase operation is the mostly cost time, even though, it cost only serveral millisecond. --------------------------------------- Posted through http://www.EmbeddedRelated.com
From: Boudewijn Dijkstra on 9 Feb 2010 03:35
Op Sun, 07 Feb 2010 22:52:12 +0100 schreef bobo <beyondsakai(a)n_o_s_p_a_m.126.com>: >> On Feb 7, 11:20=A0am, "bobo" <beyondsakai(a)n_o_s_p_a_m.126.com> wrote: >>> >On Feb 5, 8:33=3DA0pm, "bobo" <beyondsa...(a)126.com> wrote: > > "The card does it automatically, but it STILL TAKES FINITE TIME.", don't > you think the time is too long ? It depends. For how much money is that card being sold? I expect cheaper cards to perform worse on average. -- Gemaakt met Opera's revolutionaire e-mailprogramma: http://www.opera.com/mail/ (remove the obvious prefix to reply by mail) |