drivers/crypto: add Microchip RNG90 support, esp32c3-devkit enablement and documentation

[FelipeMdeO]

Summary

This PR adds support for the Microchip RNG90 in NuttX and documents the example application.

The Microchip RNG90 is a low-cost standalone hardware RNG designed to provide cryptographic-grade random numbers for embedded systems. RNG90 targets FIPS 140-ready designs and is compliant with the NIST SP 800-90A/B/C framework, making it useful for secure key generation, nonces, challenges, and other entropy-dependent operations.

Changes included:

• RNG90 driver integration in kernel/board flow (device registration and usage via /dev/rng0).
• ESP32-C3 board configuration updates for RNG90 enablement.
• New user documentation for the RNG90 example at Documentation/applications/examples/rng90/index.rst, including overview, configuration, usage, references, and hardware validation transcript.

Impact

• New hardware feature support: RNG90 TRNG device.
• New board configuration support for esp32c3-devkit.

Testing

Host:

• macOS

Target:

• esp32c3-devkit
• RNG90 connected and enabled
• Serial port: /dev/cu.wchusbserial140
• Serial settings: 115200 8N1

You can use app example in apache/nuttx-apps#3529 to test this implementation and generate same result shown below.

Build/flash:

• make -j4
• make flash ESPTOOL_PORT=

Hardware validation transcript:

nsh> uname -a
NuttX 12.6.0-RC1 4130050287-dirty Jun  7 2026 22:11:21 risc-v esp32c3-devkit

nsh> ls /dev/rng0
 /dev/rng0

nsh> rng90
RNG90 example: device /dev/rng0
Read 32 random byte(s):
0d b2 71 d1 40 1f 3c 50 52 3d c6 2c a9 74 ec 60
44 ab 67 bb c4 34 1b ac 48 62 fe b9 fd 95 c9 cb

nsh> rng90 /dev/rng0 16
RNG90 example: device /dev/rng0
Read 16 random byte(s):
ef 82 5f b7 41 f1 48 13 5a 41 16 3a 67 1b 90 f2

nsh> rng90 /dev/rng0 64
Invalid count 64, clamping to 32
RNG90 example: device /dev/rng0
Read 32 random byte(s):
bb be 2f 20 7f c8 33 8d 18 90 c8 fb 94 db bc e6
84 41 17 6f 5a be 5a 06 c3 7b f1 30 ac f2 a6 f5

[eren-terzioglu]

Please run refresh.sh tool. This command should work fine:

./tools/refresh.sh --defaults --silent esp32c3-devkit:rng90

[FelipeMdeO]

Hello @eren-terzioglu , I called refresh.sh but I can see any difference.
@simbit18 , sorry, the pipeline is crashing again. Can you help me, please?

[eren-terzioglu]

Hello @eren-terzioglu , I called refresh.sh but I can see any difference. @simbit18 , sorry, the pipeline is crashing again. Can you help me, please?

Hi,

I run the command locally and here is the output:

~/nuttxspace/nuttx$ ./tools/refresh.sh --defaults --silent esp32c3-devkit:rng90
  [1/1] Normalize esp32c3-devkit:rng90
28d27
< CONFIG_EXAMPLES_RNG90=y
Saving the new configuration file

And diff:

~/nuttxspace/nuttx$ git diff
diff --git a/boards/risc-v/esp32c3/esp32c3-devkit/configs/rng90/defconfig b/boards/risc-v/esp32c3/esp32c3-devkit/configs/rng90/defconfig
index 170cbd0ecb..d14c9e9b47 100644
--- a/boards/risc-v/esp32c3/esp32c3-devkit/configs/rng90/defconfig
+++ b/boards/risc-v/esp32c3/esp32c3-devkit/configs/rng90/defconfig
@@ -25,7 +25,6 @@ CONFIG_BUILTIN=y
 CONFIG_CRYPTO=y
 CONFIG_DEV_RNG90=y
 CONFIG_ESPRESSIF_I2C0=y
-CONFIG_EXAMPLES_RNG90=y
 CONFIG_FS_PROCFS=y
 CONFIG_IDLETHREAD_STACKSIZE=2048
 CONFIG_INIT_ENTRYPOINT="nsh_main"

If you add some test to NuttX Apps (seems yes you did in apache/nuttx-apps#3529), please mention it on PR description. CI error is normal because of version mismatch between NuttX and NuttX Apps.

Thanks for adding new support.

[eren-terzioglu]

Note: To run a CI with special parameters (e.g special version of nuttx-apps), please check https://github.com/NuttX/manual-nuttx-ci and #18568