tldr: m23 is an m0+ follow-on and m33 is an m3/m4 follow-on with configurable dsp and floating point options. Both have TrustZone. The m33 gives 20% performance boost to the m3/m4 (wonder what happened to the m7) while the m23 adds TrustZone to the m0+.
The M7 is available, ST have a range of parts as do Atmel and NXP/freescale.
The newer ST models have double precision FP, and they have just announced a new 400MHz range, doubling the clock speed by moving to a
45nm process.-- John Devereux
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