Messages in this thread | | | Subject | Re: [PATCH] i2c/busses: (mpc) Add support for SMBUS_READ_BLOCK_DATA | From | York Sun <> | Date | Wed, 16 Nov 2011 11:15:15 -0800 |
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On Wed, 2011-11-16 at 20:10 +0100, Jean Delvare wrote: > On Wed, 16 Nov 2011 10:20:38 -0800, York Sun wrote: > > On Wed, 2011-11-16 at 19:09 +0100, Jean Delvare wrote: > > > Your thinking is too focused on I2C block reads (or even block read of > > > data over the network or on disk). SMBus block read is something > > > completely different. It's not about reading 200 bytes of data and > > > receiving it in 16-byte chunks (I2C block read works that way, on > > > EEPROMs in particular.) There is no "data length" and "block size" to > > > compare to each other. It's about reading the value of _one_ register > > > and this value happens to be multi-byte. There is typically _no_ > > > register pointer increment (automatic or not) involved as can happen > > > with EEPROMs. If an SMBus block read from register N returns 10 bytes, > > > you're not going to read the next 10 bytes from register N+10. There > > > are no "next 10 bytes" to read, and register N+10 is something > > > completely unrelated. > > > > > > And for this reason, it is not possible to mix SMBus block reads with > > > byte reads, as can be done with I2C block reads. > > > > > > Also note that there is a limit of 32 bytes for SMBus block transfers, > > > per SMBus specification. All slaves and masters must comply with it. > > > > > > I hope I managed to clarify the case this time... > > > > You have made it much clear. If block size is fixed and block read > > cannot mix with byte read, shall we do this > > > > if length < block_size > > read block_size > > else { > > while (length) { > > read block_size > > length -= block_size > > } > > Which part of > > There is no "data length" and "block size" to compare to each other. > > did you not understand?
For example, if the length is 40 and the block size is 32, are you going to read 32, 72 byte or 64 byte?
York
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