Lei Wen schrieb:
On Mon, Sep 6, 2010 at 5:23 PM, Reinhard Meyer u-boot@emk-elektronik.de wrote:
Dear Lei Wen,
As mmc host limitation, the max number of block in one go
You already write it's a HOST limitation.
should be limited to 65535, and the max buffer size should not excceed 512k bytes.
Which would limit the #blocks to 1024 (assuming a 512 byte blocks)
Where does this limitation supposedly come from?
This limitation comes from the SD/MMC sepc. You could find one and check the 0x6 offset register(BLOCK COUNT REGISTER).
This might refer to certain HOST controllers, but not to Cards!
You could get that register is only 16bit width and only cound contain the 65535 block.
This register is only validate for multi-operation, like multi-read or multi-write command.
Hmm, CMD25 states: "Continuously writes blocks of data until a STOP_TRANSMISSION follows."
So the Card itself does not limit the number of blocks written in one go.
I do not mind the transfer to be split into chunks if required by some hosts, but the "number of blocks in a go" should be configurable.
And you still do not explain why the buffer size shall be limited to 512KB?
Best Regards, Reinhard