>On the AT91SAM7S, can the VCC risetime be slower than
that of Vcore?
Datasheet:
"During startup, core supply voltage (VDDCORE) slope must be superior or
equal to 6V/ms."
Atmel FAQ:
Most known SAM7 Boot Problems Question
What are the most known boot problems for SAM7?
Answer
1- VDDCORE slope constraint of 6V/ms. Only for the AT91SAM7S and AT91SAM7X.
Applicable to VDDIN when using the on-chip voltage regulator to power
VDDCORE.
If you're still having problems I'd review checklist:
http://www.atmel.com/dyn/resources/prod_documents/doc6258.pdf
Then contact local FAE, and keep in mind rev. C die release imminent.