spotreba SD karty

[Milan B.]

Ked uz mate tu dokumentaciu na stole, najdite si popis operacie write.  
Zistite, ze na ukoncenie zapisu dat do flash sa caka. (As long as the 
card is busy programming, a continuous stream of busy tokens will be 
sent to the host). A to aj v pripade multiblock write po odoslani stop 
tokenu  ... Toto cakanie na ukoncenie je povinne, vratane kontroly stavu.

Tych niekolko bufferov netvori transparentnu cache, ktora by prinasala 
zrychlenie nezavisle od sposobu prace s kartou. Napriklad vseobecna 
implementacia FAT filesystemu ju vyuzije velmi obmedzene (ak vobec),  
pretoze sekvencny zapis mnozstva dat do sektorov nasledujucich za sebou 
nie je az tak casta operacia. Ono aj sekvencny zapis suboru nemusi 
znamenat sekvencny zapis na medium - zavisi to od fragmentacie volneho 
miesta  na filesysteme. Za normalnych okolnosti sa zapise par blokov (v 
zavislosti od bloku filesystemu), upravi FAT tabulka, zase sa zapise par 
blokov ... a po kazdej operacii sa bude cakat na dokoncenie 
programovania flash.

Samozrejme, da sa to oklamat - predalokovat spojity subor a potom donho 
chrlit data cez multiblock write - ale tu sa jedna o specificky sposob, 
ktory moze zlyhat pri ciastocne zaplnenej karte ...

Takze viac bufferov v kombinacii s multiblock operaciami urychli pristup 
ku karte za  v pripade, ze sme schopni ho vyuzit vo vacsom rozsahu - ale 
na zaver aj tak musima cakat na dokoncenie programovania flash, skor ako 
karte posleme dalsi prikaz.

Podla mna, hlavne zvyusenie rychlosti kariet je v topologii a 
paralelizovaniom zapise ....

-m-


Radek Benedikt wrote:
> Dne neděle 10 květen 2009 12:26 Milan B. napsal(a):
>   
>> Skuste sa drzat temy. Rec bola o SD kartach, nie o flash pamatiach ako
>> takych, ani o diskoch ani o teorii cachovania ako takeho.
>>     
>
> Tak jo, pokud to nebudu brat obecne ale podivam se k SanDisku, tak v jejich 
> materialech o SD kartach najdu napr.
>
> Another major MultiMediaCard and SD Card design consideration is the use of
> Singleblock or Multiblock command modes. Singleblock mode reads and writes 
> data one block at a time; Multiblock mode reads and writes multiple blocks 
> until a stop command is received.
> Multiblock mode takes advantage of the multiple internal block buffers present 
> in all MultiMediaCards or SD Cards. In Multiblock mode, when one block buffer 
> gets full during write, the card gives the host access to the other empty 
> block buffers to fill while programming the first block. The card does not 
> enter a busy state until all block buffers are full.
>
> Jak je videt ty buffery tam jsou a jejich vliv take nemusi byt prave 
> zanedbatelny.
>
> Radek
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