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DMA modes and how to write ,read ,format and store files in the mount hdd of dm355 development board

laibaotang
Intellectual 400 points

 

 

1.1.1 Building drivers in Interrupt/Polling/DMA modes(source: LSP1.20_InstallationGuide.doc)

USB driver

The default mode of operation is “interrupt” or PIO. To enable DMA mode of operation, execute the following commands.

make menuconfig

Uncheck the option below – 

[]  Disable DMA (always use PIO)

[root@localhost ~]# cd  /opt/mv_pro_4.0.1/montavista/pro/devkit/lsp/ti-davinci

[root@localhost ~]# make menuconfig

question:

1.why not to turn up the option below – 

[]  Disable DMA (always use PIO)

we need Building drivers in DMA modes

2.how to write ,read ,format and store files in the  mount hdd of dm355 development board?please provide me some references.

 

 

  • TI__Mastermind 37340 points

    1) DMA makes sense when you are tranferring large amounts of data (e.g. video buffer); for most common tasks such as reading/storing variable to memory, or saving a few changes of a data file to memory, DMA may turn out to be costly; it takes time to setup DMA transaction and therefore does not make much sense for small data transfers.  Additionally, the Video Processing Subsystem (VPSS) has its own DMA engine that is always turned on; this means that any video frame that is tranfered to (capture) and from (display) DDR2 is done via DMA already.  I believe this is the reason why DMA is disabled by default in the option you described above.

    2) to read, write, store a file, you use standardized Linux APIs (open, read, write, ioctl, close); you can see the demos (encode, decode, encodedecode) included in the DVSDK as reference.  Also, not quite sure what you mean by format a file; normally you format a partition for the file system type (VFAT, JFFS2, ...) you will be supporting... is this what you meant?