Hi list, I wanted to close the loop on this with one final comment:
On 07/07/2011 10:55 PM, Eloy Paris wrote: > On 07/07/2011 04:41 PM, Paul Alfille wrote: > >> I think I'm starting to see your question. You are wondering how to read >> and write in the middle of a "file" (memory buffer). > > Yes, with the added complexity (for me to understand how things work) > that I was trying to do this from the command line, with regular Unix > utilities like "cat" . > >> The command line is an awkward place to do partial file operations. > > That's what I learned today. Perhaps "dd", which allows to specify an > offset and a read size, would work, but definitely not "cat". As Paul mentioned, there are several ways to read a block of memory from a device (for those 1-Wire devices that support this operation). To read from the command line one could use owread. However, "cat" cannot be used because it does not result in an operating system read() function call, which uses offset and size parameters that end up in a 1-Wire query (owq) structure. However, in addition to owread, I found that the "dd" utility also allows to do memory reads. Here are two ways I was able to do a device memory read using "dd": dd bs=1 count=2304 if=/owfs2/99.010203040506/generic/memory of=file.bin dd bs=2304 count=1 if=/owfs2/99.010203040506/generic/memory of=file.bin The first "dd" invocation took considerable longer than the second because, since the block size is 1 (bs=1), it actually issues 2304 1-Wire read memory commands to read a single byte each time. This results in a *lot* of overhead. It's a good stress-test of the system, though ;-) The second invocation is faster because it issues less 1-Wire read memory commands (less overhead). The number of 1-Wire read memory commands issued depends on how much memory can be read at once -- on the BAE and on my device it is 32 bytes (limitation set on the owfs side). Thanks to Paul and Pascal for their insightful comments. Cheers, Eloy Paris.- ------------------------------------------------------------------------------ All of the data generated in your IT infrastructure is seriously valuable. Why? It contains a definitive record of application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-d2d-c2 _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
