Not sure if anyone here has ever seen or used this as I've never seen it mentioned here, but there's a really neat open source IDE software for the MCS-51 family. It's layed out and works very similar to Microchip's MPLAB IDE, but it's made for MCS-51 uC's. Here's a link to it if anyone is interested in trying it out --
I've used it to write my 8051 code and it works very well with no issues. It even has a simulator that will let you run, animate and single step through your code.
Jon..... Have you used this software yet?...... I have been using it with SDCC... I found the breakpoints manager a bit.....well bad.... The other parts are good though... It does simulate (albeit slow).
Have you experienced this? It may be just with SDCC.
Yes Ian...it is what I use for all of my MCS-51 development coding, although I code in assembly hence I use the built in assembler myself.
I've also used the simulator, although I haven't tried it with break points yet. Perhaps I'll do some testing with it today and see what I come up with.