From 2ebaa9f520cc9eb58a4c3271353b83df433891f3 Mon Sep 17 00:00:00 2001
From: deadprogram <ron@hybridgroup.com>
Date: Tue, 14 Dec 2021 12:17:55 +0100
Subject: [PATCH] machine/samd51: implement TRNG for randomness

Signed-off-by: deadprogram <ron@hybridgroup.com>
---
 src/crypto/rand/rand_baremetal.go |  4 ++--
 src/machine/machine_atsamd51.go   | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/crypto/rand/rand_baremetal.go b/src/crypto/rand/rand_baremetal.go
index b5f8bc21..94b8ad65 100644
--- a/src/crypto/rand/rand_baremetal.go
+++ b/src/crypto/rand/rand_baremetal.go
@@ -1,5 +1,5 @@
-//go:build stm32wlx
-// +build stm32wlx
+//go:build stm32wlx || (sam && atsamd51) || (sam && atsame5x)
+// +build stm32wlx sam,atsamd51 sam,atsame5x
 
 package rand
 
diff --git a/src/machine/machine_atsamd51.go b/src/machine/machine_atsamd51.go
index 9b678041..ba556c6a 100644
--- a/src/machine/machine_atsamd51.go
+++ b/src/machine/machine_atsamd51.go
@@ -1,3 +1,4 @@
+//go:build (sam && atsamd51) || (sam && atsame5x)
 // +build sam,atsamd51 sam,atsame5x
 
 // Peripheral abstraction layer for the atsamd51.
@@ -2733,3 +2734,20 @@ func syncDAC() {
 	for sam.DAC.SYNCBUSY.HasBits(sam.DAC_SYNCBUSY_DATA0) {
 	}
 }
+
+var rngInitDone = false
+
+// GetRNG returns 32 bits of cryptographically secure random data
+func GetRNG() (uint32, error) {
+	if !rngInitDone {
+		// Turn on clock for TRNG
+		sam.MCLK.APBCMASK.SetBits(sam.MCLK_APBCMASK_TRNG_)
+
+		// enable
+		sam.TRNG.CTRLA.Set(sam.TRNG_CTRLA_ENABLE)
+
+		rngInitDone = true
+	}
+	ret := sam.TRNG.DATA.Get()
+	return ret, nil
+}