Feasibility of Cortex-M4 Port?

[krfkeith]

STMicroelectronics has the ridiculously low-priced Discovery dev boards for their STM32F4 MCUs.  The board itself is too limited, but it's easy enough to add anything we would need (namely, more RAM, DAC, display).  I asked on IRC about potential difficulties of such a port, and one person noted that Cortex chips use Thumb-2, which could potentially introduce some pitfalls. I am vaguely aware that Thumb is some sort of subset of the main ARM ISA, but nothing more specific than that. I do have a fairly good knowledge of programming, but I am not particularly versed in ARM (though I am willing to learn what I need to). Could anyone here with more experience shed some light on what, if any, issues might arise in this endeavor?  

EDIT:
Well, it appears as though the STM32 chips don't have a DDR controller, bummber .  But! Freescale's Kinetis processors seem to have everything else I would need, and the DRAM controller.

[torne]

It shouldn't be too difficult to get a port going on an M4, but you will need to tweak a number of bits of our assembly to make it okay for Thumb2. The majority of assembly is in codecs, though, so you shouldn't have too much trouble in the course of getting it to boot.

[saratoga]

I looked through the M4 reference manual and the assembly looks fairly similar to ARMv5E in terms of coverage, although I'm assuming its not actually compatible with it.  For things like codecs it would probably not be too hard to adapt the more important bits for the M4.  Given how power efficient the new cortex chips are supposed to be, it might not be that important anyway.

[torne]

Thumb2 is almost entirely compatible with the ARM instruction set; it adds back virtually everything Thumb was missing (at the cost of having a pretty complex decoder). There are some old fashioned things it doesn't do, but those tend to have been deprecated and replaced in ARMv7-A anyway.

[phr]

How much memory does an audio player really need, anyway?  The fancier Discovery board has 192k of ram and 1mb of flash, which is probably more than the players of the early Rockbox era had (Archos Jukebox etc).  There is supposedly a newer version of the chip in the works with 512k ram.

[saratoga]

2.5 to 4 MB depending on your screen and what features are enabled.

[gevaerts]

192k of ram and 1mb of flash, which is probably more than the players of the early Rockbox era had (Archos Jukebox etc).

Those had 2MB RAM

[wodz]

Archos Jukebox uses hardware decoder as well while CM4 port will use software decoding which needs substantial amount of ram. IIRC there was afford to port rockbox to 2MB arm target and it was proven difficult.