zephyr: Add threading support.

This commit implements the `_thread` module on the zephyr port.

Due to the fact that we are still using a rather old version of Zephyr,
`CONFIG_DYNAMIC_THREAD` is not available and therefore the stack for
threads cannot be allocated dynamically, only at compile time.  So for the
time being and for the purpose of this commit, a maximum of 4 Zephyr
threads (besides the main thread) can be created.  Once we manage to update
to the latest version of Zephyr this won't be a problem anymore.

Configuration for the nrf52840dk is added as part of this change, because
this board was used to test the threading support.

The Zephyr option `CONFIG_THREAD_CUSTOM_DATA` is used to enable threading
on a per board basis.  The `thread.conf` file is added as a convenient way
to enable threading.

Signed-off-by: danicampora <danicampora@gmail.com>

9 files changed, 419 insertions, 3 deletions

diff --git a/ports/zephyr/CMakeLists.txt b/ports/zephyr/CMakeLists.txt
index c048d92d2..c8bb1fc45 100644
--- a/ports/zephyr/CMakeLists.txt
+++ b/ports/zephyr/CMakeLists.txt
@@ -47,6 +47,7 @@ set(MICROPY_SOURCE_PORT
     mphalport.c
     uart_core.c
     zephyr_storage.c
+    mpthreadport.c
 )
 list(TRANSFORM MICROPY_SOURCE_PORT PREPEND ${MICROPY_PORT_DIR}/)
 
diff --git a/ports/zephyr/README.md b/ports/zephyr/README.md
index 3de793b2f..c463b37d1 100644
--- a/ports/zephyr/README.md
+++ b/ports/zephyr/README.md
@@ -63,6 +63,11 @@ To build for QEMU instead:
 
     $ west build -b qemu_x86 ~/micropython/ports/zephyr
 
+To build any board with the `_thread` module enabled,
+add `-DOVERLAY_CONFIG=thread.conf`, for instance:
+
+    $ west build -b frdm_k64f ~/micropython/ports/zephyr -DOVERLAY_CONFIG=thread.conf
+
 Consult the Zephyr documentation above for the list of
 supported boards.  Board configuration files appearing in `ports/zephyr/boards/`
 correspond to boards that have been tested with MicroPython and may have
diff --git a/ports/zephyr/boards/nrf52840dk_nrf52840.conf b/ports/zephyr/boards/nrf52840dk_nrf52840.conf
new file mode 100644
index 000000000..e9ec78b64
--- /dev/null
+++ b/ports/zephyr/boards/nrf52840dk_nrf52840.conf
@@ -0,0 +1,13 @@
+CONFIG_NETWORKING=n
+CONFIG_BT=y
+CONFIG_BT_DEVICE_NAME_DYNAMIC=y
+CONFIG_BT_PERIPHERAL=y
+CONFIG_BT_CENTRAL=y
+
+CONFIG_MICROPY_HEAP_SIZE=98304
+CONFIG_MAIN_STACK_SIZE=8192
+
+# CONFIG_DYNAMIC_THREAD=y
+CONFIG_THREAD_CUSTOM_DATA=y
+CONFIG_THREAD_MONITOR=y
+CONFIG_THREAD_STACK_INFO=y
diff --git a/ports/zephyr/main.c b/ports/zephyr/main.c
index c4a135aa5..47c954622 100644
--- a/ports/zephyr/main.c
+++ b/ports/zephyr/main.c
@@ -114,14 +114,20 @@ static void vfs_init(void) {
 #endif // MICROPY_VFS
 
 int real_main(void) {
-    mp_stack_ctrl_init();
-    // Make MicroPython's stack limit somewhat smaller than full stack available
-    mp_stack_set_limit(CONFIG_MAIN_STACK_SIZE - 512);
+    volatile int stack_dummy = 0;
+
+    #if MICROPY_PY_THREAD
+    struct k_thread *z_thread = (struct k_thread *)k_current_get();
+    mp_thread_init((void *)z_thread->stack_info.start, z_thread->stack_info.size / sizeof(uintptr_t));
+    #endif
 
     init_zephyr();
     mp_hal_init();
 
 soft_reset:
+    mp_stack_set_top((void *)&stack_dummy);
+    // Make MicroPython's stack limit somewhat smaller than full stack available
+    mp_stack_set_limit(CONFIG_MAIN_STACK_SIZE - 512);
     #if MICROPY_ENABLE_GC
     gc_init(heap, heap + sizeof(heap));
     #endif
@@ -160,6 +166,14 @@ soft_reset:
     machine_pin_deinit();
     #endif
 
+    #if MICROPY_PY_THREAD
+    mp_thread_deinit();
+    gc_collect();
+    #endif
+
+    gc_sweep_all();
+    mp_deinit();
+
     goto soft_reset;
 
     return 0;
@@ -171,6 +185,9 @@ void gc_collect(void) {
     void *dummy;
     gc_collect_start();
     gc_collect_root(&dummy, ((mp_uint_t)MP_STATE_THREAD(stack_top) - (mp_uint_t)&dummy) / sizeof(mp_uint_t));
+    #if MICROPY_PY_THREAD
+    mp_thread_gc_others();
+    #endif
     gc_collect_end();
 }
 
diff --git a/ports/zephyr/mpconfigport.h b/ports/zephyr/mpconfigport.h
index 94f4cc33d..024731025 100644
--- a/ports/zephyr/mpconfigport.h
+++ b/ports/zephyr/mpconfigport.h
@@ -113,6 +113,13 @@
 #define MICROPY_COMP_CONST (0)
 #define MICROPY_COMP_DOUBLE_TUPLE_ASSIGN (0)
 
+// When CONFIG_THREAD_CUSTOM_DATA is enabled, MICROPY_PY_THREAD is enabled automatically
+#ifdef CONFIG_THREAD_CUSTOM_DATA
+#define MICROPY_PY_THREAD                   (1)
+#define MICROPY_PY_THREAD_GIL               (1)
+#define MICROPY_PY_THREAD_GIL_VM_DIVISOR    (32)
+#endif
+
 void mp_hal_signal_event(void);
 #define MICROPY_SCHED_HOOK_SCHEDULED mp_hal_signal_event()
 
@@ -139,3 +146,21 @@ typedef long mp_off_t;
 // extra built in names to add to the global namespace
 #define MICROPY_PORT_BUILTINS \
     { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },
+
+#if MICROPY_PY_THREAD
+#define MICROPY_EVENT_POLL_HOOK \
+    do { \
+        extern void mp_handle_pending(bool); \
+        mp_handle_pending(true); \
+        MP_THREAD_GIL_EXIT(); \
+        k_msleep(1); \
+        MP_THREAD_GIL_ENTER(); \
+    } while (0);
+#else
+#define MICROPY_EVENT_POLL_HOOK \
+    do { \
+        extern void mp_handle_pending(bool); \
+        mp_handle_pending(true); \
+        k_msleep(1); \
+    } while (0);
+#endif
diff --git a/ports/zephyr/mpconfigport_minimal.h b/ports/zephyr/mpconfigport_minimal.h
index e819d5cf4..6c7a4c6b8 100644
--- a/ports/zephyr/mpconfigport_minimal.h
+++ b/ports/zephyr/mpconfigport_minimal.h
@@ -83,3 +83,5 @@ typedef unsigned mp_uint_t; // must be pointer size
 typedef long mp_off_t;
 
 #define MP_STATE_PORT MP_STATE_VM
+
+#define MICROPY_EVENT_POLL_HOOK
diff --git a/ports/zephyr/mpthreadport.c b/ports/zephyr/mpthreadport.c
new file mode 100644
index 000000000..0edfdee1e
--- /dev/null
+++ b/ports/zephyr/mpthreadport.c
@@ -0,0 +1,307 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Damien P. George on behalf of Pycom Ltd
+ * Copyright (c) 2017 Pycom Limited
+ * Copyright (c) 2024 Daniel Campora on behalf of REMOTE TECH LTD
+ *
+ * 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 <stdio.h>
+
+#include "py/runtime.h"
+#include "py/gc.h"
+#include "py/mpthread.h"
+#include "py/mphal.h"
+
+#if MICROPY_PY_THREAD
+
+#define DEBUG_printf(...) // printk("_thread: " __VA_ARGS__)
+
+#define MP_THREAD_MIN_STACK_SIZE                        (4 * 1024)
+#define MP_THREAD_DEFAULT_STACK_SIZE                    (MP_THREAD_MIN_STACK_SIZE + 1024)
+#define MP_THREAD_PRIORITY                              (k_thread_priority_get(k_current_get()))    // same priority as the main thread
+#define MP_THREAD_MAXIMUM_USER_THREADS                  (4)
+
+typedef enum {
+    MP_THREAD_STATUS_CREATED = 0,
+    MP_THREAD_STATUS_READY,
+    MP_THREAD_STATUS_FINISHED,
+} mp_thread_status_t;
+
+typedef struct _mp_thread_slot_t {
+    bool used;
+} mp_thread_stack_slot_t;
+
+// this structure forms a linked list, one node per active thread
+typedef struct _mp_thread_t {
+    k_tid_t id;                 // system id of thread (this is actually a pointer to z_thread below)
+    struct k_thread z_thread;   // the zephyr thread object
+    mp_thread_status_t status;  // whether the thread is created, ready, or finished
+    int16_t alive;              // whether the thread is still visible by the kernel
+    int16_t slot;               // slot index in the stack pool
+    void *arg;                  // thread Python args, a GC root pointer
+    void *stack;                // pointer to the stack
+    size_t stack_len;           // number of words in the stack
+    struct _mp_thread_t *next;
+} mp_thread_t;
+
+// the mutex controls access to the linked list
+static mp_thread_mutex_t thread_mutex;
+static mp_thread_t thread_entry0;
+static mp_thread_t *thread = NULL; // root pointer, handled by mp_thread_gc_others
+static uint8_t mp_thread_counter;
+static mp_thread_stack_slot_t stack_slot[MP_THREAD_MAXIMUM_USER_THREADS];
+
+K_THREAD_STACK_ARRAY_DEFINE(mp_thread_stack_array, MP_THREAD_MAXIMUM_USER_THREADS, MP_THREAD_DEFAULT_STACK_SIZE);
+
+static void mp_thread_iterate_threads_cb(const struct k_thread *thread, void *user_data);
+static int32_t mp_thread_find_stack_slot(void);
+
+void mp_thread_init(void *stack, uint32_t stack_len) {
+    mp_thread_set_state(&mp_state_ctx.thread);
+    // create the first entry in the linked list of all threads
+    thread_entry0.id = k_current_get();
+    thread_entry0.status = MP_THREAD_STATUS_READY;
+    thread_entry0.alive = 1;
+    thread_entry0.arg = NULL;
+    thread_entry0.stack = stack;
+    thread_entry0.stack_len = stack_len;
+    thread_entry0.next = NULL;
+    k_thread_name_set(thread_entry0.id, "mp_main");
+    mp_thread_counter = 0;
+    mp_thread_mutex_init(&thread_mutex);
+
+    // memory barrier to ensure above data is committed
+    __sync_synchronize();
+
+    thread = &thread_entry0;
+}
+
+void mp_thread_gc_others(void) {
+    mp_thread_t *prev = NULL;
+
+    if (thread == NULL) {
+        // threading not yet initialised
+        return;
+    }
+
+    mp_thread_mutex_lock(&thread_mutex, 1);
+
+    // get the kernel to iterate over all the existing threads
+    DEBUG_printf("Iterating...\n");
+    k_thread_foreach(mp_thread_iterate_threads_cb, NULL);
+    for (mp_thread_t *th = thread; th != NULL; th = th->next) {
+        // unlink non-alive thread nodes from the list
+        if ((th->status == MP_THREAD_STATUS_FINISHED) && !th->alive) {
+            if (prev != NULL) {
+                prev->next = th->next;
+            } else {
+                // move the start pointer
+                thread = th->next;
+            }
+            stack_slot[th->slot].used = false;
+            mp_thread_counter--;
+            DEBUG_printf("Collecting thread %s\n", k_thread_name_get(th->id));
+            // The "th" memory will eventually be reclaimed by the GC
+        } else {
+            th->alive = 0;
+            prev = th;
+        }
+    }
+
+    DEBUG_printf("mp_thread_gc_others from %s\n", k_thread_name_get(k_current_get()));
+
+    for (mp_thread_t *th = thread; th != NULL; th = th->next) {
+        DEBUG_printf("%s\n", k_thread_name_get(th->id));
+        gc_collect_root((void **)&th, 1);
+        gc_collect_root(&th->arg, 1);
+        // gc_collect_root(&th->stack, 1);  // will be needed later when the stack is allocated from the gc heap
+        if (th->id == k_current_get()) {
+            continue;
+        }
+        if (th->status != MP_THREAD_STATUS_READY) {
+            continue;
+        }
+        gc_collect_root(th->stack, th->stack_len);
+    }
+    mp_thread_mutex_unlock(&thread_mutex);
+}
+
+mp_state_thread_t *mp_thread_get_state(void) {
+    return (mp_state_thread_t *)k_thread_custom_data_get();
+}
+
+void mp_thread_set_state(mp_state_thread_t *state) {
+    k_thread_custom_data_set((void *)state);
+}
+
+mp_uint_t mp_thread_get_id(void) {
+    return (mp_uint_t)k_current_get();
+}
+
+void mp_thread_start(void) {
+    mp_thread_mutex_lock(&thread_mutex, 1);
+    for (mp_thread_t *th = thread; th != NULL; th = th->next) {
+        if (th->id == k_current_get()) {
+            th->status = MP_THREAD_STATUS_READY;
+            break;
+        }
+    }
+    mp_thread_mutex_unlock(&thread_mutex);
+}
+
+static void zephyr_entry(void *arg1, void *arg2, void *arg3) {
+    (void)arg3;
+
+    // arg1 contains the python thread entry point
+    if (arg1) {
+        void *(*entry)(void *) = arg1;
+        entry(arg2);
+    }
+    k_thread_abort(k_current_get());
+    for (;;) {;
+    }
+}
+
+mp_uint_t mp_thread_create_ex(void *(*entry)(void *), void *arg, size_t *stack_size, int priority, char *name) {
+    // TODO: we need to support for CONFIG_DYNAMIC_THREAD in order to dynamically create allocate the stack of a thread
+    // if (*stack_size == 0) {
+    //     *stack_size = MP_THREAD_DEFAULT_STACK_SIZE; // default stack size
+    // } else if (*stack_size < MP_THREAD_MIN_STACK_SIZE) {
+    //     *stack_size = MP_THREAD_MIN_STACK_SIZE; // minimum stack size
+    // }
+
+    // in case some threads have finished but their stack has not been collected yet
+    gc_collect();
+
+    // Allocate linked-list node (must be outside thread_mutex lock)
+    mp_thread_t *th = m_new_obj(mp_thread_t);
+
+    mp_thread_mutex_lock(&thread_mutex, 1);
+
+    int32_t _slot = mp_thread_find_stack_slot();
+    if (_slot >= 0) {
+        // create thread
+        th->id = k_thread_create(&th->z_thread, mp_thread_stack_array[_slot], K_THREAD_STACK_SIZEOF(mp_thread_stack_array[_slot]),
+            zephyr_entry, entry, arg, NULL, priority, 0, K_NO_WAIT);
+
+        if (th->id == NULL) {
+            mp_thread_mutex_unlock(&thread_mutex);
+            mp_raise_msg(&mp_type_OSError, MP_ERROR_TEXT("can't create thread"));
+        }
+
+        k_thread_name_set(th->id, (const char *)name);
+
+    } else {
+        mp_thread_mutex_unlock(&thread_mutex);
+        mp_raise_msg(&mp_type_OSError, MP_ERROR_TEXT("maximum number of threads reached"));
+    }
+
+    // add thread to linked list of all threads
+    th->status = MP_THREAD_STATUS_CREATED;
+    th->alive = 0;
+    th->slot = _slot;
+    th->arg = arg;
+    th->stack = (void *)th->z_thread.stack_info.start;
+    th->stack_len = th->z_thread.stack_info.size / sizeof(uintptr_t);
+    th->next = thread;
+    thread = th;
+
+    stack_slot[_slot].used = true;
+    mp_thread_counter++;
+
+    // adjust the stack_size to provide room to recover from hitting the limit
+    *stack_size = th->z_thread.stack_info.size - 1024;
+
+    mp_thread_mutex_unlock(&thread_mutex);
+
+    return (mp_uint_t)th->id;
+}
+
+mp_uint_t mp_thread_create(void *(*entry)(void *), void *arg, size_t *stack_size) {
+    char _name[16];
+    snprintf(_name, sizeof(_name), "mp_thread_%d", mp_thread_counter);
+    return mp_thread_create_ex(entry, arg, stack_size, MP_THREAD_PRIORITY, _name);
+}
+
+void mp_thread_finish(void) {
+    mp_thread_mutex_lock(&thread_mutex, 1);
+    for (mp_thread_t *th = thread; th != NULL; th = th->next) {
+        if (th->id == k_current_get()) {
+            th->status = MP_THREAD_STATUS_FINISHED;
+            DEBUG_printf("Finishing thread %s\n", k_thread_name_get(th->id));
+            break;
+        }
+    }
+    mp_thread_mutex_unlock(&thread_mutex);
+}
+
+void mp_thread_mutex_init(mp_thread_mutex_t *mutex) {
+    // Need a binary semaphore so a lock can be acquired on one Python thread
+    // and then released on another.
+    k_sem_init(&mutex->handle, 0, 1);
+    k_sem_give(&mutex->handle);
+}
+
+int mp_thread_mutex_lock(mp_thread_mutex_t *mutex, int wait) {
+    return k_sem_take(&mutex->handle, wait ? K_FOREVER : K_NO_WAIT) == 0;
+}
+
+void mp_thread_mutex_unlock(mp_thread_mutex_t *mutex) {
+    k_sem_give(&mutex->handle);
+}
+
+void mp_thread_deinit(void) {
+    // abort all threads except for the main thread
+    mp_thread_mutex_lock(&thread_mutex, 1);
+    for (mp_thread_t *th = thread; th != NULL; th = th->next) {
+        // don't delete the current task
+        if ((th->id != k_current_get()) && (th->status != MP_THREAD_STATUS_FINISHED)) {
+            th->status = MP_THREAD_STATUS_FINISHED;
+            DEBUG_printf("De-initializing thread %s\n", k_thread_name_get(th->id));
+            k_thread_abort(th->id);
+        }
+    }
+    mp_thread_mutex_unlock(&thread_mutex);
+}
+
+static void mp_thread_iterate_threads_cb(const struct k_thread *z_thread, void *user_data) {
+    for (mp_thread_t *th = thread; th != NULL; th = th->next) {
+        if (th->id == (struct k_thread *)z_thread) {
+            th->alive = 1;
+            DEBUG_printf("Found thread %s\n", k_thread_name_get(th->id));
+        }
+    }
+}
+
+static int32_t mp_thread_find_stack_slot(void) {
+    for (int i = 0; i < MP_THREAD_MAXIMUM_USER_THREADS; i++) {
+        if (!stack_slot[i].used) {
+            DEBUG_printf("Allocating stack slot %d\n", i);
+            return i;
+        }
+    }
+    return -1;
+}
+
+#endif // MICROPY_PY_THREAD
diff --git a/ports/zephyr/mpthreadport.h b/ports/zephyr/mpthreadport.h
new file mode 100644
index 000000000..37dd72532
--- /dev/null
+++ b/ports/zephyr/mpthreadport.h
@@ -0,0 +1,42 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Damien P. George on behalf of Pycom Ltd
+ * Copyright (c) 2017 Pycom Limited
+ * Copyright (c) 2024 Daniel Campora on behalf of REMOTE TECH LTD
+ *
+ * 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.
+ */
+
+#ifndef MICROPY_INCLUDED_ZEPHYR_MPTHREADPORT_H
+#define MICROPY_INCLUDED_ZEPHYR_MPTHREADPORT_H
+
+#include <zephyr/zephyr.h>
+
+typedef struct _mp_thread_mutex_t {
+    struct k_sem handle;
+} mp_thread_mutex_t;
+
+void mp_thread_init(void *stack, uint32_t stack_len);
+void mp_thread_gc_others(void);
+void mp_thread_deinit(void);
+
+#endif // MICROPY_INCLUDED_ZEPHYR_MPTHREADPORT_H
diff --git a/ports/zephyr/thread.conf b/ports/zephyr/thread.conf
new file mode 100644
index 000000000..af5af58dd
--- /dev/null
+++ b/ports/zephyr/thread.conf
@@ -0,0 +1,4 @@
+# CONFIG_DYNAMIC_THREAD=y
+CONFIG_THREAD_CUSTOM_DATA=y
+CONFIG_THREAD_MONITOR=y
+CONFIG_THREAD_STACK_INFO=y