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diff --git a/circuitpython/ports/raspberrypi/common-hal/os/__init__.c b/circuitpython/ports/raspberrypi/common-hal/os/__init__.c
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+++ b/circuitpython/ports/raspberrypi/common-hal/os/__init__.c
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+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2021 Scott Shawcroft for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "genhdr/mpversion.h"
+#include "py/mpconfig.h"
+#include "py/objstr.h"
+#include "py/objtuple.h"
+#include "py/qstr.h"
+
+#include "shared-bindings/os/__init__.h"
+
+#include "lib/crypto-algorithms/sha256.h"
+
+#include "hardware/structs/rosc.h"
+
+#include <string.h>
+
+STATIC const qstr os_uname_info_fields[] = {
+    MP_QSTR_sysname, MP_QSTR_nodename,
+    MP_QSTR_release, MP_QSTR_version, MP_QSTR_machine
+};
+STATIC const MP_DEFINE_STR_OBJ(os_uname_info_sysname_obj, "rp2040");
+STATIC const MP_DEFINE_STR_OBJ(os_uname_info_nodename_obj, "rp2040");
+STATIC const MP_DEFINE_STR_OBJ(os_uname_info_release_obj, MICROPY_VERSION_STRING);
+STATIC const MP_DEFINE_STR_OBJ(os_uname_info_version_obj, MICROPY_GIT_TAG " on " MICROPY_BUILD_DATE);
+STATIC const MP_DEFINE_STR_OBJ(os_uname_info_machine_obj, MICROPY_HW_BOARD_NAME " with " MICROPY_HW_MCU_NAME);
+
+
+STATIC MP_DEFINE_ATTRTUPLE(
+    os_uname_info_obj,
+    os_uname_info_fields,
+    5,
+    (mp_obj_t)&os_uname_info_sysname_obj,
+    (mp_obj_t)&os_uname_info_nodename_obj,
+    (mp_obj_t)&os_uname_info_release_obj,
+    (mp_obj_t)&os_uname_info_version_obj,
+    (mp_obj_t)&os_uname_info_machine_obj
+    );
+
+mp_obj_t common_hal_os_uname(void) {
+    return (mp_obj_t)&os_uname_info_obj;
+}
+
+// NIST Special Publication 800-90B (draft) recommends several extractors,
+// including the SHA hash family and states that if the amount of entropy input
+// is twice the number of bits output from them, that output can be considered
+// essentially fully random.  If every RANDOM_SAFETY_MARGIN bits from
+// `rosc_hw->randombit` have at least 1 bit of entropy, then this criterion is met.
+//
+// This works by seeding the `random_state` with plenty of random bits (SHA256
+// as entropy harvesting function), then using that state it as a counter input
+// (SHA256 as a CSPRNG), re-seeding at least every 256 blocks (8kB).
+//
+// In practice, `PractRand` doesn't detect any gross problems with the output
+// random numbers on samples of 1 to 8 megabytes, no matter the setting of
+// RANDOM_SAFETY_MARGIN.  (it does detect "unusual" results from time to time,
+// as it will with any RNG)
+#define RANDOM_SAFETY_MARGIN (4)
+
+static BYTE random_state[SHA256_BLOCK_SIZE];
+static void seed_random_bits(BYTE out[SHA256_BLOCK_SIZE]) {
+    CRYAL_SHA256_CTX context;
+    sha256_init(&context);
+    for (int i = 0; i < 2 * RANDOM_SAFETY_MARGIN; i++) {
+        for (int j = 0; j < SHA256_BLOCK_SIZE; j++) {
+            out[j] = rosc_hw->randombit & 1;
+            for (int k = 0; k < 8; k++) {
+                out[j] = (out[j] << 1) ^ (rosc_hw->randombit & 1);
+            }
+        }
+        sha256_update(&context, out, SHA256_BLOCK_SIZE);
+    }
+    sha256_final(&context, out);
+}
+
+static void get_random_bits(BYTE out[SHA256_BLOCK_SIZE]) {
+    if (!random_state[0]++) {
+        seed_random_bits(random_state);
+    }
+    CRYAL_SHA256_CTX context;
+    sha256_init(&context);
+    sha256_update(&context, random_state, SHA256_BLOCK_SIZE);
+    sha256_final(&context, out);
+}
+
+bool common_hal_os_urandom(uint8_t *buffer, mp_uint_t length) {
+#define ROSC_POWER_SAVE (1) // assume ROSC is not necessarily active all the time
+    #if ROSC_POWER_SAVE
+    uint32_t old_rosc_ctrl = rosc_hw->ctrl;
+    rosc_hw->ctrl = (old_rosc_ctrl & ~ROSC_CTRL_ENABLE_BITS) | (ROSC_CTRL_ENABLE_VALUE_ENABLE << 12);
+    #endif
+    while (length) {
+        size_t n = MIN(length, SHA256_BLOCK_SIZE);
+        BYTE sha_buf[SHA256_BLOCK_SIZE];
+        get_random_bits(sha_buf);
+        memcpy(buffer, sha_buf, n);
+        buffer += n;
+        length -= n;
+    }
+    #if ROSC_POWER_SAVE
+    rosc_hw->ctrl = old_rosc_ctrl;
+    #endif
+    return true;
+}