cpu/efm32/hwrng: add series 2 periph driver

cpu/efm32/periph/Makefile

@@ -1,5 +1,14 @@
 include $(RIOTCPU)/efm32/efm32-info.mk
 
+# Select the correct implementation for `periph_timer`
+ifneq (,$(filter periph_hwrng,$(USEMODULE)))
+  ifeq (1,$(EFM32_SERIES))
+    SRC += hwrng_series1.c
+  else ifeq (2,$(EFM32_SERIES))
+    SRC += hwrng_series2.c
+  endif
+endif
+
 # Select the correct implementation for `periph_rtc`
 ifneq (,$(filter periph_rtc,$(USEMODULE)))
   ifeq (0,$(EFM32_SERIES))

cpu/efm32/periph/hwrng_series2.c

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2022 SSV Software Systems GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     cpu_efm32
+ * @ingroup     drivers_periph_hwrng
+ * @{
+ *
+ * @file
+ * @brief       Hardware random generator implementation.
+ *
+ * @author      Juergen Fitschen <me@jue.yt>
+ * @}
+ */
+
+#include <assert.h>
+
+#include "cpu.h"
+
+#include "periph_conf.h"
+#include "periph/hwrng.h"
+#include "mutex.h"
+
+#include "em_cmu.h"
+#include "em_se.h"
+
+#include <string.h>
+
+void hwrng_init(void)
+{
+    /* enable clock */
+#if (_SILICON_LABS_32B_SERIES_2_CONFIG > 2)
+    CMU_ClockEnable(cmuClock_SEMAILBOX, true);
+#endif
+}
+
+static void _get_random(uint8_t *buf, unsigned int num)
+{
+    assert(num % 4 == 0);
+
+    static mutex_t mtx = MUTEX_INIT;
+
+    SE_Command_t cmd = SE_COMMAND_DEFAULT(SE_COMMAND_TRNG_GET_RANDOM);
+    SE_DataTransfer_t data_out = SE_DATATRANSFER_DEFAULT(buf, num);
+    SE_Response_t cmd_rsp;
+
+    /* prepare command */
+    SE_addDataOutput(&cmd, &data_out);
+    SE_addParameter(&cmd, num);
+
+    /* exec command */
+    mutex_lock(&mtx);
+    SE_executeCommand(&cmd);
+    SE_waitCommandCompletion();
+    cmd_rsp = SE_readCommandResponse();
+    mutex_unlock(&mtx);
+
+    (void)cmd_rsp;
+    assert(cmd_rsp == SE_RESPONSE_OK);
+}
+
+void hwrng_read(void *buf, unsigned int num)
+{
+    uint8_t *data = buf;
+    unsigned int num_extra = num & 0x3U;
+    num &= ~0x3U;
+
+    if (num > 0) {
+        _get_random(&data[0], num);
+    }
+
+    if (num_extra > 0) {
+        uint8_t tmp[4];
+        _get_random(tmp, sizeof(tmp));
+        memcpy(&data[num], &tmp, num_extra);
+    }
+}