ricardgb opened a new pull request, #19400:
URL: https://github.com/apache/nuttx/pull/19400
## Summary
The RP2350 (rp23xx) embeds an Arm CryptoCell-style true random number
generator — a sampled ring oscillator conditioned by von-Neumann, CRNGT and
autocorrelation health tests, presenting 192 bits in the six `EHR_DATA`
words —
but there is no driver for it, so `/dev/urandom` on rp23xx is the software
xorshift PRNG.
This adds `arch/arm/src/rp23xx/rp23xx_rng.c`, a polling driver that serves
the
conditioned hardware bits as `/dev/random` and `/dev/urandom`. Entropy is
drawn
rarely (an mbedtls CTR_DRBG seeds once and reseeds occasionally), so a
blocking
poll is used rather than interrupt plumbing; health-test failures discard the
block and re-arm the source, so only conditioned entropy is ever returned.
New `CONFIG_RP23XX_TRNG` `select`s `ARCH_HAVE_RNG`, which switches
`/dev/urandom`
from the software PRNG to the hardware source (backing `getrandom()` and
thus any
entropy consumer, e.g. mbedtls).
## Impact
- rp23xx gains a real hardware entropy source; opt-in via
`CONFIG_RP23XX_TRNG`.
- No change when the option is off (default `n`).
## Testing
Tested on a Raspberry Pi Pico 2 W:
- `/dev/random` and `/dev/urandom` register from the TRNG;
- a 32-byte read returns at real ring-oscillator sampling latency (~10 ms);
- two independent 32-byte samples differ (live, non-stuck source);
- the CryptoCell CRNGT continuous test — which would stall a stuck source —
passes, and mbedtls seeds its CTR_DRBG from `/dev/urandom` successfully.
---
*Disclosure: this change was prepared by an AI agent (Claude Code) at the
direction of the author, who reviewed and tested it on hardware before
submission.*
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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