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I'm making an application in Xcode 4 for MAC which purpose is to draw a graph of an ECG reading. The reading is supposed to be received over USB/serial. I therefore need to write code for the application that can read and write characters to the USB port.

I think that the ebst way to do this is by using the IO Kit and POSIX...

To be honest, the documentation on the IOKit that I've found on the developer website has been pretty hard to understand.

Are there any basic tutorials on using the IOKit to talk to and get information from hardware devices?

Failing that, are there basic tutorials on the fundamental concepts of OSX architecture? When they start talking about mach tasks and kern results, I get totally lost.

Thanks in advance

Cyberlurk
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1 Answers1

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If your device is basically just a serial device plugged into a standard USB/serial adapter, you shouldn't need to drop to the IOKit level. Locate the UNIX character device for your serial port and open that for unbuffered file I/O. You may want to traverse the I/O kit registry purely for enumerating ports, but you shouldn't need it for actual I/O.

To get you started with that, you'll want to create a matching dictionary with:

IOServiceMatching(kIOSerialBSDServiceValue);

and then get the returned devices' file paths via the kIOCalloutDeviceKey property.

If it's not a standard USB/serial adapter, you'll need to use IOKit. I unfortunately don't know any better web resources than Apple's on the topic of USB and drivers, but there are books:

  • OS X and iOS Kernel Programming is specifically targeted at (aspiring) driver programmers. It contains 2 chapters on USB, one for USB fundamentals and kernel space drivers, and one on user-space USB drivers. You should hopefully be able to get up and running with those. (Disclaimer: I was one of the tech reviewers for this book; I don't get paid to advertise it, however, and I don't get royalties)

  • Mac OS X Internals is starting to show its age (it's current as of OS X 10.4) and isn't specifically a driver development book. It does give very detailed descriptions of many parts of OS X and its kernel though. Not an awful lot on USB, if I remember correctly.

For USB, you have 2 options: user space and kenel space drivers. Unless you have a good reason to do it in the kernel, I suggest doing it in user space. The APIs are very different, the kernel API is C++, userspace is C. (no, I didn't mix those up) when looking at documentation, make sure you're looking at the right one of the 2 - they're both called I/O Kit!

pmdj
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