samd: Use unique id for USB serial number.

projectgus · projectgus · commit ec9be419811f · 2023-11-08T10:37:04.000+11:00
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 &lt;angus@redyak.com.au&gt;
diff --git 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
@@ -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
@@ -40,6 +40,14 @@ void USB_Handler_wrapper(void);
 void sercom_enable(Sercom *spi, int state);
 void sercom_register_irq(int sercom_id, void (*sercom_irq_handler));
 
+typedef struct {
+    uint8_t bytes[16];
+} _samd_unique_id_t;
+
+// 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
@@ -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) {
