micropython · andrewleech · Apr 18, 2026 · Apr 18, 2026 · Apr 18, 2026 · Apr 18, 2026
diff --git a/.github/workflows/ports_unix.yml b/.github/workflows/ports_unix.yml
@@ -99,6 +99,8 @@ jobs:
         # This avoids the annoying situation of the job failing on every push to a fork (if no token is set).
         fail_ci_if_error: ${{ secrets.CODECOV_TOKEN != '' || github.repository_owner == 'micropython' }}
         verbose: true
+        flags: unix-coverage-64bit
+        name: unix-coverage-64bit
         # note: when a fork opens a PR into MicroPython repo, the pull_request trigger can't access
         # secrets so this token value will be empty (codecov will do a 'tokenless' upload).
         token: ${{ secrets.CODECOV_TOKEN }}
@@ -125,6 +127,18 @@ jobs:
       run: tools/ci.sh native_mpy_modules_32bit_build
     - name: Test importing .mpy generated by mpy_ld.py
       run: tools/ci.sh unix_coverage_32bit_run_native_mpy_tests
+    - name: Run gcov coverage analysis
+      run: |
+        (cd ports/unix && gcov -o build-coverage/py ../../py/*.c || true)
+        (cd ports/unix && gcov -o build-coverage/extmod ../../extmod/*.c || true)
+    - name: Upload coverage to Codecov
+      uses: codecov/codecov-action@v6
+      with:
+        fail_ci_if_error: ${{ secrets.CODECOV_TOKEN != '' || github.repository_owner == 'micropython' }}
+        verbose: true
+        flags: unix-coverage-32bit
+        name: unix-coverage-32bit
+        token: ${{ secrets.CODECOV_TOKEN }}
     - name: Print failures
       if: failure()
       run: tests/run-tests.py --print-failures

diff --git a/docs/library/machine.RTC.rst b/docs/library/machine.RTC.rst
@@ -102,6 +102,11 @@ Methods
 
    Availability: esp32, esp8266 ports.
 
+   .. note::
+
+      For cross-port persistent storage, see :data:`machine.backup_memory`
+      which is available on more ports and provides direct memoryview access.
+
 Constants
 ---------
 

diff --git a/docs/library/machine.rst b/docs/library/machine.rst
@@ -49,6 +49,90 @@ Example use (registers are specific to an stm32 microcontroller):
     # read PA3
     value = (machine.mem32[GPIOA + GPIO_IDR] >> 3) & 1
 
+.. data:: backup_memory
+
+   A writable `memoryview` over persistent hardware memory that survives
+   restarts, including :ref:`soft_reset` and `machine.deepsleep()`.
+
+   The element type depends on the port's hardware alignment requirements:
+   ``'B'`` (unsigned byte) on ports with byte-addressable backup memory,
+   ``'I'`` (unsigned 32-bit) on ports backed by word-sized registers.
+   Use ``machine.backup_memory.itemsize`` to discover the access granularity
+   at runtime.
+
+   The total size in bytes is ``len(mem) * mem.itemsize``, where ``len(mem)``
+   is the number of elements and ``mem.itemsize`` is the size of each element.
+   For example, on a port with 4 word-sized registers, ``len(mem)`` is 4 and
+   ``mem.itemsize`` is 4, giving 16 bytes total. On a port with 4096 bytes
+   of byte-addressable backup SRAM, ``len(mem)`` is 4096 and ``mem.itemsize``
+   is 1.
+
+   Usage::
+
+      import machine
+
+      mem = machine.backup_memory
+      mem[0] = 0x12345678                # write element 0
+      print(hex(mem[0]))                 # read element 0
+      print(len(mem))                    # number of elements
+      print(mem.itemsize)                # bytes per element
+      print(len(mem) * mem.itemsize)     # total bytes available
+
+   The total byte size and backing hardware vary by port:
+
+   ======  ===================================  =============  ==============
+   Port    Backing storage                      Total bytes    Battery-backed
+   ======  ===================================  =============  ==============
+   alif    Backup SRAM                          4096           yes
+   esp32   RTC slow memory                      2048           no
+   mimxrt  SNVS LPGPR registers (4-8 per chip)  16-32          yes
+   rp2     Watchdog scratch registers (8)       32             no
+   samd    Backup RAM (SAMD51 only)             8192           yes
+   stm32   Backup SRAM (F4/F7/H5/H7/U5/N6)      2048-8192      yes
+   stm32   RTC BKP registers (other families)   20-128         yes
+   ======  ===================================  =============  ==============
+
+   .. note::
+
+      On esp32 and rp2, data persists across :ref:`soft_reset` and
+      `machine.deepsleep()` wake but is lost on power-off and on
+      poweron-style resets. On esp32 in particular this includes pressing
+      the EN/RESET button on most dev boards, which the chip reports as a
+      power-on reset.
+
+   Some registers may be reserved by the system depending on port and board
+   configuration. These are exposed in the memoryview but should not be
+   overwritten by application code:
+
+   ======  ==============  =========================================================
+   Port    Register(s)     Used by
+   ======  ==============  =========================================================
+   mimxrt  LPGPR[3]        UF2 bootloader double-tap (when ``USE_UF2_BOOTLOADER``)
+   rp2     scratch[4-7]    pico-sdk ``watchdog_reboot()`` / ``machine.deepsleep()``
+   stm32   BKP0R           Arduino bootloader (Portenta H7, Giga, Opta, Nicla)
+   stm32   BKP16R-BKP18R   ``rfcore_firmware.py`` on STM32WB
+   stm32   last BKP reg    clock frequency (``MICROPY_HW_CLK_LAST_FREQ``)
+   stm32   BKP31R (N6)     mboot bootloader entry
+   ======  ==============  =========================================================
+
+   The buffer allows direct register access and can be combined with
+   ``uctypes`` for structured layouts::
+
+      import machine, uctypes
+
+      mem = machine.backup_memory
+
+      # Structured access via uctypes (check len(mem) for your board)
+      layout = {
+          "flags": (0 * 4, uctypes.UINT32),    # register 0
+          "counter": (1 * 4, uctypes.UINT32),  # register 1
+      }
+      regs = uctypes.struct(uctypes.addressof(mem), layout)
+      regs.flags = 0x01
+      print(regs.counter)
+
+   Availability: alif, esp32, mimxrt, rp2, samd, stm32 ports.
+
 Reset related functions
 -----------------------
 

diff --git a/extmod/extmod.cmake b/extmod/extmod.cmake
@@ -9,6 +9,7 @@ set(MICROPY_SOURCE_EXTMOD
     ${MICROPY_EXTMOD_DIR}/btstack/modbluetooth_btstack.c
     ${MICROPY_EXTMOD_DIR}/machine_adc.c
     ${MICROPY_EXTMOD_DIR}/machine_adc_block.c
+    ${MICROPY_EXTMOD_DIR}/machine_backup_memory.c
     ${MICROPY_EXTMOD_DIR}/machine_bitstream.c
     ${MICROPY_EXTMOD_DIR}/machine_can.c
     ${MICROPY_EXTMOD_DIR}/machine_i2c.c

diff --git a/extmod/extmod.mk b/extmod/extmod.mk
@@ -4,6 +4,7 @@
 SRC_EXTMOD_C += \
 	extmod/machine_adc.c \
 	extmod/machine_adc_block.c \
+	extmod/machine_backup_memory.c \
 	extmod/machine_bitstream.c \
 	extmod/machine_can.c \
 	extmod/machine_i2c.c \

diff --git a/extmod/machine_backup_memory.c b/extmod/machine_backup_memory.c
@@ -0,0 +1,55 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2026 Andrew Leech
+ *
+ * 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 "py/mpconfig.h"
+
+#if MICROPY_PY_MACHINE_BACKUP_MEMORY
+
+#include "py/obj.h"
+#include "py/objarray.h"
+
+// Validate port configuration at compile time.
+#if !MICROPY_PY_BUILTINS_MEMORYVIEW
+#error "backup_memory requires MICROPY_PY_BUILTINS_MEMORYVIEW"
+#endif
+#if MICROPY_HW_BACKUP_MEMORY_ITEMSIZE != 1 && MICROPY_HW_BACKUP_MEMORY_ITEMSIZE != 4
+#error "MICROPY_HW_BACKUP_MEMORY_ITEMSIZE must be 1 or 4"
+#endif
+
+// Select memoryview typecode based on item size. The 0x80 flag marks the
+// memoryview as read-write.
+#if MICROPY_HW_BACKUP_MEMORY_ITEMSIZE == 1
+#define BACKUP_MEMORY_TYPECODE ('B' | 0x80)
+#elif MICROPY_HW_BACKUP_MEMORY_ITEMSIZE == 4
+#define BACKUP_MEMORY_TYPECODE ('I' | 0x80)
+#endif
+
+const MP_DEFINE_MEMORYVIEW_OBJ(machine_backup_memory_obj,
+    BACKUP_MEMORY_TYPECODE, 0,
+    MICROPY_HW_BACKUP_MEMORY_BYTES / MICROPY_HW_BACKUP_MEMORY_ITEMSIZE,
+    MICROPY_HW_BACKUP_MEMORY_ADDR);
+
+#endif // MICROPY_PY_MACHINE_BACKUP_MEMORY
diff --git a/extmod/modmachine.c b/extmod/modmachine.c
@@ -149,6 +149,9 @@ static const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_mem16), MP_ROM_PTR(&machine_mem16_obj) },
     { MP_ROM_QSTR(MP_QSTR_mem32), MP_ROM_PTR(&machine_mem32_obj) },
     #endif
+    #if MICROPY_PY_MACHINE_BACKUP_MEMORY
+    { MP_ROM_QSTR(MP_QSTR_backup_memory), MP_ROM_PTR(&machine_backup_memory_obj) },
+    #endif
 
     // Miscellaneous functions.
     #if MICROPY_PY_MACHINE_BARE_METAL_FUNCS

diff --git a/extmod/modmachine.h b/extmod/modmachine.h
@@ -198,6 +198,12 @@ extern const machine_mem_obj_t machine_mem8_obj;
 extern const machine_mem_obj_t machine_mem16_obj;
 extern const machine_mem_obj_t machine_mem32_obj;
 
+// Object for machine.backup_memory (static memoryview over persistent storage).
+#if MICROPY_PY_MACHINE_BACKUP_MEMORY
+#include "py/objarray.h"
+extern const mp_obj_array_t machine_backup_memory_obj;
+#endif
+
 // These classes correspond to machine.Type entries in the machine module.
 // Their Python bindings are implemented in extmod, and their implementation
 // is provided by a port.

diff --git a/ports/alif/mpconfigport.h b/ports/alif/mpconfigport.h
@@ -147,6 +147,17 @@
 #define MICROPY_PY_MACHINE_UART                 (1)
 #define MICROPY_PY_MACHINE_UART_INCLUDEFILE     "ports/alif/machine_uart.c"
 #define MICROPY_PY_MACHINE_UART_IRQ             (1)
+#ifndef MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_PY_MACHINE_BACKUP_MEMORY        (1)
+#endif
+#if MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_HW_BACKUP_MEMORY_BYTES          (4096)
+// The 4KB region at 0x4902C000 is in peripheral space and does not
+// support sub-word writes (byte writes zero unaddressed bytes of the
+// containing word). Expose as uint32 memoryview to enforce word access.
+#define MICROPY_HW_BACKUP_MEMORY_ITEMSIZE       (4)
+#define MICROPY_HW_BACKUP_MEMORY_ADDR           ((void *)0x4902C000)
+#endif
 #define MICROPY_PY_NETWORK                      (CORE_M55_HP)
 #ifndef MICROPY_PY_NETWORK_HOSTNAME_DEFAULT
 #define MICROPY_PY_NETWORK_HOSTNAME_DEFAULT     "mpy-alif"

diff --git a/ports/esp32/machine_rtc.c b/ports/esp32/machine_rtc.c
@@ -56,10 +56,6 @@ typedef struct _machine_rtc_obj_t {
     If MICROPY_HW_RTC_USER_MEM_MAX is set to 0, the RTC.memory() functionality will be not
     be compiled which frees some extra flash and RTC memory.
 */
-#ifndef MICROPY_HW_RTC_USER_MEM_MAX
-#define MICROPY_HW_RTC_USER_MEM_MAX     2048
-#endif
-
 // A board can enable MICROPY_HW_RTC_MEM_INIT_ALWAYS to always clear out RTC memory on boot.
 // Defaults to RTC_NOINIT_ATTR so the user memory survives WDT resets and the like.
 #if MICROPY_HW_RTC_MEM_INIT_ALWAYS

diff --git a/ports/esp32/mpconfigport.h b/ports/esp32/mpconfigport.h
@@ -165,6 +165,19 @@
 #define MICROPY_PY_MACHINE_UART_IRQ         (1)
 #define MICROPY_PY_MACHINE_WDT              (1)
 #define MICROPY_PY_MACHINE_WDT_INCLUDEFILE  "ports/esp32/machine_wdt.c"
+#ifndef MICROPY_HW_RTC_USER_MEM_MAX
+#define MICROPY_HW_RTC_USER_MEM_MAX         2048
+#endif
+// machine.backup_memory exposes the RTC user memory as a byte memoryview.
+// RTC.memory() coexists but uses separate length tracking; writes via
+// backup_memory won't update RTC.memory()'s length, and vice versa.
+#if MICROPY_HW_RTC_USER_MEM_MAX > 0
+extern uint8_t rtc_user_mem_data[];
+#define MICROPY_PY_MACHINE_BACKUP_MEMORY    (1)
+#define MICROPY_HW_BACKUP_MEMORY_BYTES      (MICROPY_HW_RTC_USER_MEM_MAX)
+#define MICROPY_HW_BACKUP_MEMORY_ITEMSIZE   (1)
+#define MICROPY_HW_BACKUP_MEMORY_ADDR       ((void *)&rtc_user_mem_data[0])
+#endif
 #ifndef MICROPY_PY_NETWORK
 #define MICROPY_PY_NETWORK (1)
 #endif

diff --git a/ports/mimxrt/mpconfigport.h b/ports/mimxrt/mpconfigport.h
@@ -139,6 +139,14 @@ uint32_t trng_random_u32(void);
 #endif
 #define MICROPY_PY_ONEWIRE                  (1)
 #define MICROPY_PY_MACHINE_BOOTLOADER       (1)
+#ifndef MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_PY_MACHINE_BACKUP_MEMORY    (1)
+#endif
+#if MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_HW_BACKUP_MEMORY_BYTES      (SNVS_LPGPR_COUNT * 4)
+#define MICROPY_HW_BACKUP_MEMORY_ITEMSIZE   (4)
+#define MICROPY_HW_BACKUP_MEMORY_ADDR       ((void *)&SNVS->LPGPR[0])
+#endif
 
 // fatfs configuration used in ffconf.h
 #define MICROPY_FATFS_ENABLE_LFN            (2)

diff --git a/ports/rp2/mpconfigport.h b/ports/rp2/mpconfigport.h
@@ -30,6 +30,7 @@
 #include "hardware/flash.h"
 #include "hardware/spi.h"
 #include "hardware/sync.h"
+#include "hardware/structs/watchdog.h"
 #include "pico/binary_info.h"
 #include "pico/multicore.h"
 #include "mpconfigboard.h"
@@ -191,6 +192,14 @@
 #define MICROPY_PY_MACHINE_UART_IRQ             (1)
 #define MICROPY_PY_MACHINE_WDT                  (1)
 #define MICROPY_PY_MACHINE_WDT_INCLUDEFILE      "ports/rp2/machine_wdt.c"
+#ifndef MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_PY_MACHINE_BACKUP_MEMORY        (1)
+#endif
+#if MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_HW_BACKUP_MEMORY_BYTES          (sizeof(watchdog_hw->scratch))
+#define MICROPY_HW_BACKUP_MEMORY_ITEMSIZE       (4)
+#define MICROPY_HW_BACKUP_MEMORY_ADDR           ((void *)&watchdog_hw->scratch[0])
+#endif
 #define MICROPY_PY_MACHINE_FREQ_NUM_ARGS_MAX    (2)
 #define MICROPY_PY_ONEWIRE                      (1)
 #define MICROPY_VFS                             (1)

diff --git a/ports/samd/mcu/samd51/mpconfigmcu.h b/ports/samd/mcu/samd51/mpconfigmcu.h
@@ -28,6 +28,15 @@ unsigned long trng_random_u32(void);
 
 #define VFS_BLOCK_SIZE_BYTES            (2048) //
 
+#ifndef MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_PY_MACHINE_BACKUP_MEMORY        (1)
+#endif
+#if MICROPY_PY_MACHINE_BACKUP_MEMORY
+#define MICROPY_HW_BACKUP_MEMORY_BYTES          (BKUPRAM_SIZE)
+#define MICROPY_HW_BACKUP_MEMORY_ITEMSIZE       (1)
+#define MICROPY_HW_BACKUP_MEMORY_ADDR           ((void *)BKUPRAM_ADDR)
+#endif
+
 #ifndef MICROPY_HW_UART_TXBUF
 #define MICROPY_HW_UART_TXBUF           (1)
 #endif