From 5e3f0e7f8580d854eb451adbf164a9ab97386d4c Mon Sep 17 00:00:00 2001
From: Angus Gratton <angus@redyak.com.au>
Date: Wed, 8 Nov 2023 09:48:33 +1100
Subject: [PATCH 1/3] samd: Switch to shared TinyUSB implementation.

Functionality and code size don't really change, but removes port-specific
code in favour of shared code.

(The MSC implemented in shared/tinyusb depends on some functions in the
pico-sdk, so this change doesn't make this available for samd.)

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>
---
 ports/samd/Makefile                  |   6 +-
 ports/samd/mcu/samd21/mpconfigmcu.mk |   2 +
 ports/samd/mcu/samd51/mpconfigmcu.mk |   2 +
 ports/samd/mpconfigport.h            |  16 ++++
 ports/samd/tusb_port.c               | 122 ---------------------------
 ports/samd/{tusb_config.h => usbd.c} |  35 ++++----
 6 files changed, 41 insertions(+), 142 deletions(-)
 delete mode 100644 ports/samd/tusb_port.c
 rename ports/samd/{tusb_config.h => usbd.c} (64%)

diff --git a/ports/samd/Makefile b/ports/samd/Makefile
index 12223e6ded8f4..95d0f3bd18f48 100644
--- a/ports/samd/Makefile
+++ b/ports/samd/Makefile
@@ -55,6 +55,7 @@ INC += -I$(TOP)/lib/asf4/$(MCU_SERIES_LOWER)/hpl/tc
 INC += -I$(TOP)/lib/asf4/$(MCU_SERIES_LOWER)/include
 INC += -I$(TOP)/lib/asf4/$(MCU_SERIES_LOWER)/include/pio
 INC += -I$(TOP)/lib/tinyusb/src
+INC += -I$(TOP)/shared/tinyusb/
 
 MAKE_PINS = boards/make-pins.py
 BOARD_PINS = $(BOARD_DIR)/pins.csv
@@ -117,7 +118,7 @@ SRC_C += \
 	samd_qspiflash.c \
 	samd_soc.c \
 	samd_spiflash.c \
-	tusb_port.c \
+	usbd.c \
 
 SHARED_SRC_C += \
 	drivers/dht/dht.c \
@@ -133,7 +134,8 @@ SHARED_SRC_C += \
 	shared/runtime/sys_stdio_mphal.c \
 	shared/timeutils/timeutils.c \
 	shared/tinyusb/mp_cdc_common.c \
-	shared/tinyusb/mp_usbd.c
+	shared/tinyusb/mp_usbd.c \
+	shared/tinyusb/mp_usbd_descriptor.c \
 
 ASF4_SRC_C += $(addprefix lib/asf4/$(MCU_SERIES_LOWER)/,\
 	hal/src/hal_atomic.c \
diff --git a/ports/samd/mcu/samd21/mpconfigmcu.mk b/ports/samd/mcu/samd21/mpconfigmcu.mk
index 35f442d86990a..b3092837cbd15 100644
--- a/ports/samd/mcu/samd21/mpconfigmcu.mk
+++ b/ports/samd/mcu/samd21/mpconfigmcu.mk
@@ -1,5 +1,7 @@
 CFLAGS_MCU += -mtune=cortex-m0plus -mcpu=cortex-m0plus -msoft-float
 
+CFLAGS_MCU += -DCFG_TUSB_MCU=OPT_MCU_SAMD21
+
 MPY_CROSS_MCU_ARCH = armv6m
 
 MICROPY_HW_CODESIZE ?= 184K
diff --git a/ports/samd/mcu/samd51/mpconfigmcu.mk b/ports/samd/mcu/samd51/mpconfigmcu.mk
index c706331aca459..0201bacffeef1 100644
--- a/ports/samd/mcu/samd51/mpconfigmcu.mk
+++ b/ports/samd/mcu/samd51/mpconfigmcu.mk
@@ -1,5 +1,7 @@
 CFLAGS_MCU += -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard
 
+CFLAGS_MCU += -DCFG_TUSB_MCU=OPT_MCU_SAMD51
+
 MPY_CROSS_MCU_ARCH = armv7m
 
 MICROPY_HW_CODESIZE ?= 368K
diff --git a/ports/samd/mpconfigport.h b/ports/samd/mpconfigport.h
index 91a7c1a10d879..497ca9a87004e 100644
--- a/ports/samd/mpconfigport.h
+++ b/ports/samd/mpconfigport.h
@@ -62,6 +62,13 @@
 #define MICROPY_HW_ENABLE_USBDEV            (1)
 #define MICROPY_HW_USB_CDC_1200BPS_TOUCH    (1)
 
+#if MICROPY_HW_ENABLE_USBDEV
+// Enable USB-CDC serial port
+#ifndef MICROPY_HW_USB_CDC
+#define MICROPY_HW_USB_CDC (1)
+#endif
+#endif
+
 // Control over Python builtins
 #define MICROPY_PY_BUILTINS_BYTES_HEX       (1)
 #define MICROPY_PY_BUILTINS_MEMORYVIEW      (1)
@@ -141,6 +148,15 @@
 
 #define MP_STATE_PORT MP_STATE_VM
 
+// Miscellaneous settings
+
+#ifndef MICROPY_HW_USB_VID
+#define MICROPY_HW_USB_VID (0xf055)
+#endif
+#ifndef MICROPY_HW_USB_PID
+#define MICROPY_HW_USB_PID (0x9802)
+#endif
+
 // Additional entries for use with pendsv_schedule_dispatch.
 #ifndef MICROPY_BOARD_PENDSV_ENTRIES
 #define MICROPY_BOARD_PENDSV_ENTRIES
diff --git a/ports/samd/tusb_port.c b/ports/samd/tusb_port.c
deleted file mode 100644
index e56ef0fd6af00..0000000000000
--- a/ports/samd/tusb_port.c
+++ /dev/null
@@ -1,122 +0,0 @@
-/*
- * This file is part of the MicroPython project, http://micropython.org/
- *
- * The MIT License (MIT)
- *
- * Copyright (c) 2019 Damien P. George
- *
- * 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 "samd_soc.h"
-#include "tusb.h"
-
-#ifndef MICROPY_HW_USB_VID
-#define MICROPY_HW_USB_VID (0xf055)
-#define MICROPY_HW_USB_PID (0x9802)
-#endif
-
-#define USBD_DESC_LEN (TUD_CONFIG_DESC_LEN + TUD_CDC_DESC_LEN)
-#define USBD_MAX_POWER_MA (250)
-
-#define USBD_ITF_CDC (0) // needs 2 interfaces
-#define USBD_ITF_MAX (2)
-
-#define USBD_CDC_EP_CMD (0x81)
-#define USBD_CDC_EP_OUT (0x02)
-#define USBD_CDC_EP_IN (0x82)
-#define USBD_CDC_CMD_MAX_SIZE (8)
-#define USBD_CDC_IN_OUT_MAX_SIZE (64)
-
-#define USBD_STR_0 (0x00)
-#define USBD_STR_MANUF (0x01)
-#define USBD_STR_PRODUCT (0x02)
-#define USBD_STR_SERIAL (0x03)
-#define USBD_STR_CDC (0x04)
-
-// Note: descriptors returned from callbacks must exist long enough for transfer to complete
-
-static const tusb_desc_device_t usbd_desc_device = {
-    .bLength = sizeof(tusb_desc_device_t),
-    .bDescriptorType = TUSB_DESC_DEVICE,
-    .bcdUSB = 0x0200,
-    .bDeviceClass = TUSB_CLASS_MISC,
-    .bDeviceSubClass = MISC_SUBCLASS_COMMON,
-    .bDeviceProtocol = MISC_PROTOCOL_IAD,
-    .bMaxPacketSize0 = CFG_TUD_ENDOINT0_SIZE,
-    .idVendor = MICROPY_HW_USB_VID,
-    .idProduct = MICROPY_HW_USB_PID,
-    .bcdDevice = 0x0100,
-    .iManufacturer = USBD_STR_MANUF,
-    .iProduct = USBD_STR_PRODUCT,
-    .iSerialNumber = USBD_STR_SERIAL,
-    .bNumConfigurations = 1,
-};
-
-static const uint8_t usbd_desc_cfg[USBD_DESC_LEN] = {
-    TUD_CONFIG_DESCRIPTOR(1, USBD_ITF_MAX, USBD_STR_0, USBD_DESC_LEN,
-        TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, USBD_MAX_POWER_MA),
-
-    TUD_CDC_DESCRIPTOR(USBD_ITF_CDC, USBD_STR_CDC, USBD_CDC_EP_CMD,
-        USBD_CDC_CMD_MAX_SIZE, USBD_CDC_EP_OUT, USBD_CDC_EP_IN, USBD_CDC_IN_OUT_MAX_SIZE),
-};
-
-static const char *const usbd_desc_str[] = {
-    [USBD_STR_MANUF] = "MicroPython",
-    [USBD_STR_PRODUCT] = "Board in FS mode",
-    [USBD_STR_SERIAL] = "000000000000", // TODO
-    [USBD_STR_CDC] = "Board CDC",
-};
-
-const uint8_t *tud_descriptor_device_cb(void) {
-    return (const uint8_t *)&usbd_desc_device;
-}
-
-const uint8_t *tud_descriptor_configuration_cb(uint8_t index) {
-    (void)index;
-    return usbd_desc_cfg;
-}
-
-const uint16_t *tud_descriptor_string_cb(uint8_t index, uint16_t langid) {
-    #define DESC_STR_MAX (20)
-    static uint16_t desc_str[DESC_STR_MAX];
-
-    uint8_t len;
-    if (index == 0) {
-        desc_str[1] = 0x0409; // supported language is English
-        len = 1;
-    } else {
-        if (index >= sizeof(usbd_desc_str) / sizeof(usbd_desc_str[0])) {
-            return NULL;
-        }
-        const char *str = usbd_desc_str[index];
-        for (len = 0; len < DESC_STR_MAX - 1 && str[len]; ++len) {
-            desc_str[1 + len] = str[len];
-        }
-    }
-
-    // first byte is length (including header), second byte is string type
-    desc_str[0] = (TUSB_DESC_STRING << 8) | (2 * len + 2);
-
-    return desc_str;
-}
-
-void USB_Handler_wrapper(void) {
-    tud_int_handler(0);
-}
diff --git a/ports/samd/tusb_config.h b/ports/samd/usbd.c
similarity index 64%
rename from ports/samd/tusb_config.h
rename to ports/samd/usbd.c
index 07fa680cbbb6b..90f2e1bfd95ed 100644
--- a/ports/samd/tusb_config.h
+++ b/ports/samd/usbd.c
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2019 Damien P. George
+ * Copyright (c) 2023 Angus Gratton
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,25 +23,24 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
-#ifndef MICROPY_INCLUDED_SAMD_TUSB_CONFIG_H
-#define MICROPY_INCLUDED_SAMD_TUSB_CONFIG_H
 
-// Common configuration
+#include "py/mpconfig.h"
 
-#if defined(MCU_SAMD21)
-#define CFG_TUSB_MCU                OPT_MCU_SAMD21
-#elif defined(MCU_SAMD51)
-#define CFG_TUSB_MCU                OPT_MCU_SAMD51
-#endif
-#define CFG_TUSB_RHPORT0_MODE       OPT_MODE_DEVICE
-#define CFG_TUSB_MEM_SECTION
-#define CFG_TUSB_MEM_ALIGN          TU_ATTR_ALIGNED(4)
+#if MICROPY_HW_ENABLE_USBDEV
+
+#include "mp_usbd.h"
+#include "string.h"
+#include "tusb.h"
 
-// Device configuration
+#define SERIAL_TODO "000000000000" // TODO
 
-#define CFG_TUD_ENDOINT0_SIZE       (64)
-#define CFG_TUD_CDC                 (1)
-#define CFG_TUD_CDC_RX_BUFSIZE      (64)
-#define CFG_TUD_CDC_TX_BUFSIZE      (64)
+void mp_usbd_port_get_serial_number(char *serial_buf) {
+    MP_STATIC_ASSERT(sizeof(SERIAL_TODO) <= MICROPY_HW_USB_DESC_STR_MAX);
+    strcpy(serial_buf, SERIAL_TODO);
+}
 
-#endif // MICROPY_INCLUDED_SAMD_TUSB_CONFIG_H
+void USB_Handler_wrapper(void) {
+    tud_int_handler(0);
+}
+
+#endif

From f567a9255a2f801c8e47d8a1468f1c0415971fe4 Mon Sep 17 00:00:00 2001
From: Angus Gratton <angus@redyak.com.au>
Date: Wed, 8 Nov 2023 10:34:57 +1100
Subject: [PATCH 2/3] shared/tinyusb: Add a helper for hex string conversion.

Change the rp2 and renesas-ra ports to use the helper function.

Saves copy-pasta, at the small cost of one more function call in the
firmware (if not using LTO).

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>
---
 ports/renesas-ra/usbd.c  | 11 ++---------
 ports/rp2/usbd.c         | 11 ++---------
 shared/tinyusb/mp_usbd.c | 10 ++++++++++
 shared/tinyusb/mp_usbd.h |  5 +++++
 4 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/ports/renesas-ra/usbd.c b/ports/renesas-ra/usbd.c
index 7047503864f61..e7252b5f7acfb 100644
--- a/ports/renesas-ra/usbd.c
+++ b/ports/renesas-ra/usbd.c
@@ -34,15 +34,8 @@
 
 void mp_usbd_port_get_serial_number(char *serial_buf) {
     const bsp_unique_id_t *id = R_BSP_UniqueIdGet();
-    // convert to hex
-    int hexlen = sizeof(id->unique_id_bytes) * 2;
-    MP_STATIC_ASSERT(hexlen <= MICROPY_HW_USB_DESC_STR_MAX);
-    for (int i = 0; i < hexlen; i += 2) {
-        static const char *hexdig = "0123456789abcdef";
-        serial_buf[i] = hexdig[id->unique_id_bytes[i / 2] >> 4];
-        serial_buf[i + 1] = hexdig[id->unique_id_bytes[i / 2] & 0x0f];
-    }
-    serial_buf[hexlen] = 0;
+    MP_STATIC_ASSERT(sizeof(id->unique_id_bytes) * 2 <= MICROPY_HW_USB_DESC_STR_MAX);
+    mp_usbd_hex_str(serial_buf, id->unique_id_bytes, sizeof(id->unique_id_bytes));
 }
 
 #endif
diff --git a/ports/rp2/usbd.c b/ports/rp2/usbd.c
index 568b6284169b2..8724f802f074d 100644
--- a/ports/rp2/usbd.c
+++ b/ports/rp2/usbd.c
@@ -36,15 +36,8 @@
 void mp_usbd_port_get_serial_number(char *serial_buf) {
     pico_unique_board_id_t id;
     pico_get_unique_board_id(&id);
-    // convert to hex
-    int hexlen = sizeof(id.id) * 2;
-    MP_STATIC_ASSERT(hexlen <= MICROPY_HW_USB_DESC_STR_MAX);
-    for (int i = 0; i < hexlen; i += 2) {
-        static const char *hexdig = "0123456789abcdef";
-        serial_buf[i] = hexdig[id.id[i / 2] >> 4];
-        serial_buf[i + 1] = hexdig[id.id[i / 2] & 0x0f];
-    }
-    serial_buf[hexlen] = 0;
+    MP_STATIC_ASSERT(sizeof(id.id) * 2 <= MICROPY_HW_USB_DESC_STR_MAX);
+    mp_usbd_hex_str(serial_buf, id.id, sizeof(id.id));
 }
 
 #endif
diff --git a/shared/tinyusb/mp_usbd.c b/shared/tinyusb/mp_usbd.c
index 55af3d4fb4792..74b3f074927b8 100644
--- a/shared/tinyusb/mp_usbd.c
+++ b/shared/tinyusb/mp_usbd.c
@@ -62,4 +62,14 @@ static void mp_usbd_task_callback(mp_sched_node_t *node) {
     mp_usbd_task();
 }
 
+void mp_usbd_hex_str(char *out_str, const uint8_t *bytes, size_t bytes_len) {
+    size_t hex_len = bytes_len * 2;
+    for (int i = 0; i < hex_len; i += 2) {
+        static const char *hexdig = "0123456789abcdef";
+        out_str[i] = hexdig[bytes[i / 2] >> 4];
+        out_str[i + 1] = hexdig[bytes[i / 2] & 0x0f];
+    }
+    out_str[hex_len] = 0;
+}
+
 #endif
diff --git a/shared/tinyusb/mp_usbd.h b/shared/tinyusb/mp_usbd.h
index 340637c95f9c3..83a8f8617c08d 100644
--- a/shared/tinyusb/mp_usbd.h
+++ b/shared/tinyusb/mp_usbd.h
@@ -36,4 +36,9 @@ void mp_usbd_task(void);
 // Can write a string up to MICROPY_HW_USB_DESC_STR_MAX characters long, plus terminating byte.
 extern void mp_usbd_port_get_serial_number(char *buf);
 
+// Most ports need to write a hexadecimal serial number from a byte array, this
+// is a helper function for this. out_str must be long enough to hold a string of total
+// length (2 * bytes_len + 1) (including NUL terminator).
+void mp_usbd_hex_str(char *out_str, const uint8_t *bytes, size_t bytes_len);
+
 #endif // MICROPY_INCLUDED_SHARED_TINYUSB_USBD_H

From 8b1980ad450ea2b34af4b831a8c655ba08dee800 Mon Sep 17 00:00:00 2001
From: Angus Gratton <angus@redyak.com.au>
Date: Wed, 8 Nov 2023 10:37:04 +1100
Subject: [PATCH 3/3] samd: Use unique id for USB serial number.

Replaces the previous all-zeroes "TODO" serial number.

Requires refactoring the low-level unique_id routine out from modmachine.c.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>
---
 ports/samd/modmachine.c   | 42 +++------------------------------------
 ports/samd/mpconfigport.h |  5 +++++
 ports/samd/samd_soc.c     | 36 +++++++++++++++++++++++++++++++++
 ports/samd/samd_soc.h     |  8 ++++++++
 ports/samd/usbd.c         |  9 +++++----
 5 files changed, 57 insertions(+), 43 deletions(-)

diff --git a/ports/samd/modmachine.c b/ports/samd/modmachine.c
index 7c3d96eb01364..8c4808075e7a3 100644
--- a/ports/samd/modmachine.c
+++ b/ports/samd/modmachine.c
@@ -92,45 +92,9 @@ STATIC mp_obj_t machine_freq(size_t n_args, const mp_obj_t *args) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_freq_obj, 0, 1, machine_freq);
 
 STATIC mp_obj_t machine_unique_id(void) {
-    // Each device has a unique 128-bit serial number which is a concatenation of four 32-bit
-    // words contained at the following addresses. The uniqueness of the serial number is
-    // guaranteed only when using all 128 bits.
-    // Atmel SAM D21E / SAM D21G / SAM D21J
-    // SMART ARM-Based Microcontroller
-    // DATASHEET
-    // 9.6 (SAMD51) or 9.3.3 (or 10.3.3 depending on which manual)(SAMD21) Serial Number
-    //
-    // EXAMPLE (SAMD21)
-    // ----------------
-    // OpenOCD:
-    // Word0:
-    // > at91samd21g18.cpu mdw 0x0080A00C 1
-    // 0x0080a00c: 6e27f15f
-    // Words 1-3:
-    // > at91samd21g18.cpu mdw 0x0080A040 3
-    // 0x0080a040: 50534b54 332e3120 ff091645
-    //
-    // MicroPython (this code and same order as shown in Arduino IDE)
-    // >>> binascii.hexlify(machine.unique_id())
-    // b'6e27f15f50534b54332e3120ff091645'
-
-    #if defined(MCU_SAMD21)
-    uint32_t *id_addresses[4] = {(uint32_t *)0x0080A00C, (uint32_t *)0x0080A040,
-                                 (uint32_t *)0x0080A044, (uint32_t *)0x0080A048};
-    #elif defined(MCU_SAMD51)
-    uint32_t *id_addresses[4] = {(uint32_t *)0x008061FC, (uint32_t *)0x00806010,
-                                 (uint32_t *)0x00806014, (uint32_t *)0x00806018};
-    #endif
-    uint8_t raw_id[16];
-
-    for (int i = 0; i < 4; i++) {
-        for (int k = 0; k < 4; k++) {
-            // 'Reverse' the read bytes into a 32 bit word (Consistent with Arduino)
-            raw_id[4 * i + k] = (*(id_addresses[i]) >> (24 - k * 8)) & 0xff;
-        }
-    }
-
-    return mp_obj_new_bytes((byte *)&raw_id, sizeof(raw_id));
+    samd_unique_id_t id;
+    samd_get_unique_id(&id);
+    return mp_obj_new_bytes((byte *)&id.bytes, sizeof(id.bytes));
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_0(machine_unique_id_obj, machine_unique_id);
 
diff --git a/ports/samd/mpconfigport.h b/ports/samd/mpconfigport.h
index 497ca9a87004e..3684457b48e06 100644
--- a/ports/samd/mpconfigport.h
+++ b/ports/samd/mpconfigport.h
@@ -67,6 +67,11 @@
 #ifndef MICROPY_HW_USB_CDC
 #define MICROPY_HW_USB_CDC (1)
 #endif
+// SAMD unique ID is 16 bytes (hex string == 32)
+#ifndef MICROPY_HW_USB_DESC_STR_MAX
+#define MICROPY_HW_USB_DESC_STR_MAX (32)
+#endif
+
 #endif
 
 // Control over Python builtins
diff --git a/ports/samd/samd_soc.c b/ports/samd/samd_soc.c
index ad5910301cfc3..dcfff9dc22744 100644
--- a/ports/samd/samd_soc.c
+++ b/ports/samd/samd_soc.c
@@ -153,3 +153,39 @@ void sercom_deinit_all(void) {
 }
 
 #endif
+
+void samd_get_unique_id(samd_unique_id_t *id) {
+    // Atmel SAM D21E / SAM D21G / SAM D21J
+    // SMART ARM-Based Microcontroller
+    // DATASHEET
+    // 9.6 (SAMD51) or 9.3.3 (or 10.3.3 depending on which manual)(SAMD21) Serial Number
+    //
+    // EXAMPLE (SAMD21)
+    // ----------------
+    // OpenOCD:
+    // Word0:
+    // > at91samd21g18.cpu mdw 0x0080A00C 1
+    // 0x0080a00c: 6e27f15f
+    // Words 1-3:
+    // > at91samd21g18.cpu mdw 0x0080A040 3
+    // 0x0080a040: 50534b54 332e3120 ff091645
+    //
+    // MicroPython (this code and same order as shown in Arduino IDE)
+    // >>> binascii.hexlify(machine.unique_id())
+    // b'6e27f15f50534b54332e3120ff091645'
+
+    #if defined(MCU_SAMD21)
+    uint32_t *id_addresses[4] = {(uint32_t *)0x0080A00C, (uint32_t *)0x0080A040,
+                                 (uint32_t *)0x0080A044, (uint32_t *)0x0080A048};
+    #elif defined(MCU_SAMD51)
+    uint32_t *id_addresses[4] = {(uint32_t *)0x008061FC, (uint32_t *)0x00806010,
+                                 (uint32_t *)0x00806014, (uint32_t *)0x00806018};
+    #endif
+
+    for (int i = 0; i < 4; i++) {
+        for (int k = 0; k < 4; k++) {
+            // 'Reverse' the read bytes into a 32 bit word (Consistent with Arduino)
+            id->bytes[4 * i + k] = (*(id_addresses[i]) >> (24 - k * 8)) & 0xff;
+        }
+    }
+}
diff --git a/ports/samd/samd_soc.h b/ports/samd/samd_soc.h
index 90a5a57ffa14e..707d2f8edfa98 100644
--- a/ports/samd/samd_soc.h
+++ b/ports/samd/samd_soc.h
@@ -30,6 +30,10 @@
 #include "sam.h"
 #include "clock_config.h"
 
+typedef struct _samd_unique_id_t {
+    uint8_t bytes[16];
+} samd_unique_id_t;
+
 extern Sercom *sercom_instance[];
 
 void samd_init(void);
@@ -40,6 +44,10 @@ void USB_Handler_wrapper(void);
 void sercom_enable(Sercom *spi, int state);
 void sercom_register_irq(int sercom_id, void (*sercom_irq_handler));
 
+// Each device has a unique 128-bit serial number. The uniqueness of the serial number is
+// guaranteed only when using all 128 bits.
+void samd_get_unique_id(samd_unique_id_t *id);
+
 #define SERCOM_IRQ_TYPE_UART  (0)
 #define SERCOM_IRQ_TYPE_SPI   (1)
 #define SERCOM_IRQ_TYPE_I2C   (2)
diff --git a/ports/samd/usbd.c b/ports/samd/usbd.c
index 90f2e1bfd95ed..2e3200ad7d2b0 100644
--- a/ports/samd/usbd.c
+++ b/ports/samd/usbd.c
@@ -31,12 +31,13 @@
 #include "mp_usbd.h"
 #include "string.h"
 #include "tusb.h"
-
-#define SERIAL_TODO "000000000000" // TODO
+#include "samd_soc.h"
 
 void mp_usbd_port_get_serial_number(char *serial_buf) {
-    MP_STATIC_ASSERT(sizeof(SERIAL_TODO) <= MICROPY_HW_USB_DESC_STR_MAX);
-    strcpy(serial_buf, SERIAL_TODO);
+    samd_unique_id_t id;
+    samd_get_unique_id(&id);
+    MP_STATIC_ASSERT(sizeof(id.bytes) * 2 <= MICROPY_HW_USB_DESC_STR_MAX);
+    mp_usbd_hex_str(serial_buf, id.bytes, sizeof(id.bytes));
 }
 
 void USB_Handler_wrapper(void) {