Boy, would I like to be able to see a few more tools in the bag of tricks available to us when we debug. Using printfs works for many debugging tasks, but the really tough problems need something more.

Specifically, I'd like the ability to

1. Display the compiler's assembly code output next to the source code input.
2. Turn down the optimization level in the compiler, or defeat it completely.
3. Generate a "break" by means of the USB-host JTAG connection. This would interrupt the processor and report back the current execution address (useful in conjunction with the printout mentioned in point 1, above). Then that that portion of the code could then be instrumented with printfs, etc.

Have you looked at LPCXpresso version ? It comes with USB-Jtag for less than the cost a mbed.

Full interactive debugging with multiple breakpoints, data watch, etc, is commonplace with comprehensive development tools. I use IAR for ARM, with Seeger JTAG. The flash-breakpoints are wonderful, meaning I can have many active breakpoints in the code. IAR's system is called C-Spy; Keil has something similar. I preferred IAR's. Also can back-trace the stack after a crash. And so on. But these do cost, like USD$4K. Mine uses a USB dongle for the license so I can move around easily. Well worth it for professional debugging where labor costs are not zero.

I have evaluated IAR and others, I find that IAR is over priced not worth it. Code Red is about 1/4 IAR price and Eclipse IDE is much better than IAR.

IAR's C-Spy with the JTAG flash breakpoints and stack back-trace is what helps me a great deal. I didn't realize this importance during my download/evaluate of the candidates some time back. The user/IDE per se isn't as important, and doesn't differ much among IAR, Keil, Eclipse, et al.

They all have that trace features with JTAG. Otherwise they would not be called IDE but an Editor. It is the need for JTAG debugging that I bough the LCPXpresso. Can't do that with mbed online tools. LCPXpresso is $30, JTAG included & CodeRed IDE for up to 128KB of code. Not the fastest JTAG one but very usable. Full license is $1K. Eclipse show the data type of a variable under the cursor while editing and value while debugging. That is also very useful. I may be wrong but I have not seen that feature with IAR.

In the end, it's all a mater of taste. For me IAR is out of the question. Eclipse is not the best IDE either. I don't personally like Eclipse but is so far the best I could get for embedded dev. I have used Microsoft & Borland (now CodeGear) IDE. Those are really the best IDE but not for embedded dev. I have yet see any embedded IDE that come close to those.

Does CodeRed include debugging with flash breakpoints, where you can click on the C source and set an unlimited number of breakpoints? That's what's really useful to me. Along with very fast JTAG writing of my 100KB program (like 3 seconds).

unlimited breakpoints, I'm not sure. I hardly use more then 4-5. you can check on their website

http://www.code-red-tech.com/products.php#comparison