Hello, I was wondering if anyone knew of a company that makes external hard disks with an integrated real-time port that allows you to store data directly to the hard disk and the external hard disk would have some connection to a computer either parallel or USB. I'm looking for a solution to capture 32-bits of data at a rate of 20Mhz and a co-worker mentioned that a long time ago he used something similar to an external hard disk with a real-time port. I was looking for solution that could capture the data without the need for a computer, but could connect to a computer after the data has been collected.
80MB/s may be pushing the envelope a bit for today's disk drives, but may be possible with a RAID setup. You're going to need something in there to take care of the file system so the PC can read the data. The above sorta points to a PCish sort of embedded thing. How much data do you need to record? What price point?
Speed issue noted, but you don't need a file system, or at least more than a very degenerate one.
A file system is usefull when you want to organize you disk and not simply treat it like a tape drive. In this application, treating like a tape drive may be fine - you just start at the first sector of the LBA and write as many as you feel like. Okay, it might be nice to know how many your wrote, and optionally set the starting address, but there are ways of doing that without making a design go much beyond a state machine in an FPGA.
But given that the next post offers a fairly high budget, a RAID array in a server class PC, or several PC's sharing the load, may make sense. It might be possible to develop custom logic far below that price, but unless they need a lot of them or it's compelling as a design challenge there's not much point.
True, but a nonstandard filesystem is going to make reading the disk a tad more complicated. OTOH, a nonstandard filesystem may be required to get the speed.
I was thinking about disk drive's STR and 90MB/s is about the best on the market today for average STR. However, that is an average and it falls off towards the center. Another problem is that STR is *read* performance. Writes are a different kettle and sustained write speed isn't often specified. There are other issues with writes being committed and such. ...could get sticky.
True, but a FS makes operating on the data a little easier. I doubt there he needs *all* 96GB per go. If the OP does, capturing the data is only the start of the headaches. ;-)
Even a PC is kinda tight. 20MHz (80MHz) on the PCI bus is kinda iffy. Double that and it's... Synchronizing several PCs sounds difficult too.
I did a similar thing, on a different scale, 20 years ago. I built a "logic analyzer" to capture all of the I/O on microprocessors (or peripheral chips). The intention was to capture interesting events from a system and translate them into a test program for a logic test system. The hardware ended up being 128bits wide and 1Mb deep at up to 50MHz (or 256b x .5mb at 25MHz). As you say, it was an interesting challenge and I had a boss with deep pockets. ;-) The hardware alone was over $50K (even with a free source of DRAM).
Twenty minutes is about 96GB so you're not going to get away with using only the outside zone of a single disk. Splitting the data into a couple of streams shouldn't be too hard and 40MB/s should be relatively easy with a fast/modern drive. The hardware should be simple, but $50K doesn't allow much for engineering.
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