nrf: Add support for VfsRom filesystem.

The implementation uses the object based capabilities, which avoids
complication about different flash block sizes.  The ROM partition is
placed between the text and writable filesystem sections, and the latter
size is unchanged.  VfsRom sizes are:
- NRF51x22: 12K
- NRF52832: 128K
- NRF52840: 256K
- NRF9160:  256K

Use frozen `_boot.py` to set up and mount the filesystem, replacing a mix
of C-Code and Python code.  The mkfs part has been simplified to save code.

Tested with Microbit and Arduino Nano Connect.

Signed-off-by: Damien George <damien@micropython.org>
Signed-off-by: robert-hh <robert@hammelrath.com>

Author: robert-hh

ports/nrf/boards/memory.ld

@@ -8,10 +8,12 @@ _head_size     = DEFINED(_sd_size) ? _sd_size : _bootloader_head_size;
 _head_ram      = DEFINED(_sd_ram)  ? _sd_ram : _bootloader_head_ram_size;
 _sd_size       = DEFINED(_sd_size) ? _sd_size : 0;
 _sd_ram        = DEFINED(_sd_ram)  ? _sd_ram : 0;
+_micropy_hw_romfs_part0_size = DEFINED(_micropy_hw_romfs_part0_size) ? _micropy_hw_romfs_part0_size : 0;
 _fs_size       = DEFINED(_fs_size) ? _fs_size : 64K; /* TODO: set to 0 if not using the filesystem */
-_app_size      = _flash_size - _head_size - _fs_size  - _bootloader_tail_size;
+_app_size      = _flash_size - _head_size - _micropy_hw_romfs_part0_size - _fs_size - _bootloader_tail_size;
 _app_start     = _head_size;
-_fs_start      = _head_size + _app_size;
+_micropy_hw_romfs_part0_start = _head_size + _app_size;
+_fs_start      = _micropy_hw_romfs_part0_start + _micropy_hw_romfs_part0_size;
 _fs_end        = _fs_start + _fs_size;
 _app_ram_start = 0x20000000 + _head_ram;
 _app_ram_size  = _ram_size - _head_ram;

ports/nrf/boards/nrf51x22_256k_16k.ld

@@ -6,6 +6,7 @@ GROUP(-lgcc -lc -lnosys)
 
 _flash_size = 256K;
 _ram_size = 16K;
+_micropy_hw_romfs_part0_size = 12K;
 
 /* Default stack size when there is no SoftDevice */
 _stack_size        = 4K;

ports/nrf/boards/nrf51x22_256k_32k.ld

@@ -6,6 +6,7 @@ GROUP(-lgcc -lc -lnosys)
 
 _flash_size = 256K;
 _ram_size = 32K;
+_micropy_hw_romfs_part0_size = 12K;
 
 /* Default stack size when there is no SoftDevice */
 _stack_size        = 4K;

ports/nrf/boards/nrf52832_512k_64k.ld

@@ -4,6 +4,7 @@
 
 _flash_size = 512K;
 _ram_size   = 64K;
+_micropy_hw_romfs_part0_size = 128K;
 
 /* produce a link error if there is not this amount of RAM for these sections */
 _stack_size = 8K;

ports/nrf/boards/nrf52840_1M_256k.ld

@@ -4,6 +4,7 @@
 
 _flash_size = 1M;
 _ram_size   = 256K;
+_micropy_hw_romfs_part0_size = 256K;
 
 /* produce a link error if there is not this amount of RAM for these sections */
 _stack_size = 8K;

ports/nrf/boards/nrf9160_1M_256k.ld

@@ -7,6 +7,7 @@ _ram_size   = 256K;
 _sd_size = 0x00008000;
 _sd_ram  = 0x00020000;
 _fs_size = 80K;
+_micropy_hw_romfs_part0_size = 256K;
 
 /* produce a link error if there is not this amount of RAM for these sections */
 _stack_size = 32K;

ports/nrf/main.c

@@ -177,22 +177,8 @@ void MP_NORETURN _start(void) {
 
     #if MICROPY_HW_ENABLE_INTERNAL_FLASH_STORAGE
     flashbdev_init();
-
-    // Try to mount the flash on "/flash" and chdir to it for the boot-up directory.
-    mp_obj_t mount_point = MP_OBJ_NEW_QSTR(MP_QSTR__slash_flash);
-    int ret = mp_vfs_mount_and_chdir_protected((mp_obj_t)&nrf_flash_obj, mount_point);
-
-    if ((ret == -MP_ENODEV) || (ret == -MP_EIO)) {
-        pyexec_frozen_module("_mkfs.py", false); // Frozen script for formatting flash filesystem.
-        ret = mp_vfs_mount_and_chdir_protected((mp_obj_t)&nrf_flash_obj, mount_point);
-    }
-
-    if (ret != 0) {
-        printf("MPY: can't mount flash\n");
-    } else {
-        mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR__slash_flash));
-        mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR__slash_flash_slash_lib));
-    }
+    // Execute _boot.py to set up the filesystem.
+    pyexec_frozen_module("_boot.py", false);
     #endif
 
     #if MICROPY_MBFS

ports/nrf/modules/manifest.py

@@ -1,2 +1,2 @@
-module("_mkfs.py", base_path="$(PORT_DIR)/modules/scripts", opt=3)
+module("_boot.py", base_path="$(PORT_DIR)/modules/scripts", opt=3)
 include("$(MPY_DIR)/extmod/asyncio")

ports/nrf/modules/nrf/flashbdev.c

@@ -183,12 +183,26 @@ static mp_obj_t nrf_flashbdev_make_new(const mp_obj_type_t *type, size_t n_args,
     return MP_OBJ_FROM_PTR(self);
 }
 
+static mp_int_t nrf_flashbdev_get_buffer(mp_obj_t self_in, mp_buffer_info_t *bufinfo, mp_uint_t flags) {
+    nrf_flash_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    if (flags == MP_BUFFER_READ) {
+        bufinfo->buf = (void *)self->start;
+        bufinfo->len = self->len;
+        bufinfo->typecode = 'B';
+        return 0;
+    } else {
+        // Unsupported.
+        return 1;
+    }
+}
+
 MP_DEFINE_CONST_OBJ_TYPE(
     nrf_flashbdev_type,
     MP_QSTR_Flash,
     MP_TYPE_FLAG_NONE,
     make_new, nrf_flashbdev_make_new,
     print, nrf_flashbdev_print,
+    buffer, nrf_flashbdev_get_buffer,
     locals_dict, &nrf_flashbdev_locals_dict
     );
 
@@ -202,4 +216,34 @@ void flashbdev_init(void) {
     nrf_flash_obj.len = num_pages * FLASH_PAGESIZE;
 }
 
+#if MICROPY_VFS_ROM
+
+extern byte _micropy_hw_romfs_part0_start[];
+extern byte _micropy_hw_romfs_part0_size[];
+
+#define MICROPY_HW_ROMFS_BASE ((uint32_t)_micropy_hw_romfs_part0_start)
+#define MICROPY_HW_ROMFS_BYTES ((uint32_t)_micropy_hw_romfs_part0_size)
+
+static nrf_flash_obj_t nrf_flash_romfs_obj = {
+    .base = { &nrf_flashbdev_type },
+    .start = MICROPY_HW_ROMFS_BASE, // Get from MCU-Specific loader script.
+    .len = MICROPY_HW_ROMFS_BYTES, // Get from MCU-Specific loader script.
+};
+
+mp_obj_t mp_vfs_rom_ioctl(size_t n_args, const mp_obj_t *args) {
+    if (MICROPY_HW_ROMFS_BYTES <= 0) {
+        return MP_OBJ_NEW_SMALL_INT(-MP_EINVAL);
+    }
+    switch (mp_obj_get_int(args[0])) {
+        case MP_VFS_ROM_IOCTL_GET_NUMBER_OF_SEGMENTS:
+            return MP_OBJ_NEW_SMALL_INT(1);
+        case MP_VFS_ROM_IOCTL_GET_SEGMENT:
+            return MP_OBJ_FROM_PTR(&nrf_flash_romfs_obj);
+        default:
+            return MP_OBJ_NEW_SMALL_INT(-MP_EINVAL);
+    }
+}
+
+#endif // MICROPY_VFS_ROM
+
 #endif // MICROPY_PY_NRF && MICROPY_HW_ENABLE_INTERNAL_FLASH_STORAGE

ports/nrf/modules/scripts/_boot.py

@@ -0,0 +1,28 @@
+def setup_fs():
+    import gc
+    import vfs
+    import sys
+    import nrf
+    import os
+
+    fs_type = getattr(vfs, "VfsLfs2", getattr(vfs, "VfsLfs1", getattr(vfs, "VfsFat", None)))
+    try:
+        bdev = nrf.Flash()
+        vfs.mount(bdev, "/flash")
+    except:
+        if fs_type is not None:
+            try:
+                fs_type.mkfs(bdev)
+                vfs.mount(bdev, "/flash")
+            except:
+                return
+
+    os.chdir("/flash")
+    sys.path.append("/flash")
+    sys.path.append("/flash/lib")
+
+    gc.collect()
+
+
+setup_fs()
+del setup_fs