lwip: Adopted lightweight mbox implementation based on event flags

Reduces the size of an mbox object from 180 bytes (45w) to 72 bytes
(18w). Since the mbox is used in many places in lwip as a lightweight
message buffer, this saves roughly 1kB of ram.

Author: geky

features/FEATURE_LWIP/lwip-interface/lwip-sys/arch/lwip_sys_arch.c

@@ -124,15 +124,21 @@ u32_t sys_now(void) {
 err_t sys_mbox_new(sys_mbox_t *mbox, int queue_sz) {
     if (queue_sz > MB_SIZE)
         error("sys_mbox_new size error\n");
-    
+
+    mbox->post_idx = 0;
+    mbox->fetch_idx = 0;
     memset(mbox->queue, 0, sizeof(mbox->queue));
+
     memset(&mbox->data, 0, sizeof(mbox->data));
-    mbox->attr.mq_mem = mbox->queue;
-    mbox->attr.mq_size = sizeof(mbox->queue);
     mbox->attr.cb_mem = &mbox->data;
     mbox->attr.cb_size = sizeof(mbox->data);
-    mbox->id = osMessageQueueNew(queue_sz, sizeof(void *), &mbox->attr);
-    return (mbox->id == NULL) ? (ERR_MEM) : (ERR_OK);
+    mbox->id = osEventFlagsNew(&mbox->attr);
+    if (mbox->id == NULL)
+        error("sys_mbox_new create error\n");
+
+    osEventFlagsSet(mbox->id, SYS_MBOX_POST_EVENT);
+
+    return ERR_OK;
 }
 
 /*---------------------------------------------------------------------------*
@@ -146,7 +152,7 @@ err_t sys_mbox_new(sys_mbox_t *mbox, int queue_sz) {
  *      sys_mbox_t *mbox         -- Handle of mailbox
  *---------------------------------------------------------------------------*/
 void sys_mbox_free(sys_mbox_t *mbox) {
-    if (osMessageQueueGetCount(mbox->id) != 0)
+    if (mbox->post_idx != mbox->fetch_idx)
         error("sys_mbox_free error\n");
 }
 
@@ -160,8 +166,19 @@ void sys_mbox_free(sys_mbox_t *mbox) {
  *      void *msg              -- Pointer to data to post
  *---------------------------------------------------------------------------*/
 void sys_mbox_post(sys_mbox_t *mbox, void *msg) {
-    if (osMessageQueuePut(mbox->id, &msg, 0, osWaitForever) != osOK)
-        error("sys_mbox_post error\n");
+    osEventFlagsWait(mbox->id, SYS_MBOX_POST_EVENT,
+            osFlagsWaitAny | osFlagsNoClear, osWaitForever);
+
+    int state = osKernelLock();
+
+    mbox->queue[mbox->post_idx % MB_SIZE] = msg;
+    mbox->post_idx += 1;
+
+    osEventFlagsSet(mbox->id, SYS_MBOX_FETCH_EVENT);
+    if (mbox->post_idx - mbox->fetch_idx == MB_SIZE-1)
+        osEventFlagsClear(mbox->id, SYS_MBOX_POST_EVENT);
+
+    osKernelRestoreLock(state);
 }
 
 /*---------------------------------------------------------------------------*
@@ -178,8 +195,22 @@ void sys_mbox_post(sys_mbox_t *mbox, void *msg) {
  *                                  if not.
  *---------------------------------------------------------------------------*/
 err_t sys_mbox_trypost(sys_mbox_t *mbox, void *msg) {
-    osStatus_t status = osMessageQueuePut(mbox->id, &msg, 0, 0);
-    return (status == osOK) ? (ERR_OK) : (ERR_MEM);
+    uint32_t flags = osEventFlagsWait(mbox->id, SYS_MBOX_POST_EVENT,
+            osFlagsWaitAny | osFlagsNoClear, 0);
+    if (!(flags & SYS_MBOX_POST_EVENT))
+        return ERR_MEM;
+
+    int state = osKernelLock();
+
+    mbox->queue[mbox->post_idx % MB_SIZE] = msg;
+    mbox->post_idx += 1;
+
+    osEventFlagsSet(mbox->id, SYS_MBOX_FETCH_EVENT);
+    if (mbox->post_idx - mbox->fetch_idx == MB_SIZE-1)
+        osEventFlagsClear(mbox->id, SYS_MBOX_POST_EVENT);
+
+    osKernelRestoreLock(state);
+    return ERR_OK;
 }
 
 /*---------------------------------------------------------------------------*
@@ -208,12 +239,23 @@ err_t sys_mbox_trypost(sys_mbox_t *mbox, void *msg) {
  *                                  of milliseconds until received.
  *---------------------------------------------------------------------------*/
 u32_t sys_arch_mbox_fetch(sys_mbox_t *mbox, void **msg, u32_t timeout) {
-    u32_t start = us_ticker_read();
-    
-    osStatus_t res = osMessageQueueGet(mbox->id, msg, NULL, (timeout != 0)?(timeout):(osWaitForever));
-    if (res != osOK)
+    uint32_t start = us_ticker_read();
+    uint32_t flags = osEventFlagsWait(mbox->id, SYS_MBOX_FETCH_EVENT,
+            osFlagsWaitAny | osFlagsNoClear, (timeout ? timeout : osWaitForever));
+    if (!(flags & SYS_MBOX_FETCH_EVENT))
         return SYS_ARCH_TIMEOUT;
 
+    int state = osKernelLock();
+
+    if (msg)
+        *msg = mbox->queue[mbox->fetch_idx % MB_SIZE];
+    mbox->fetch_idx += 1;
+
+    osEventFlagsSet(mbox->id, SYS_MBOX_POST_EVENT);
+    if (mbox->post_idx == mbox->fetch_idx)
+        osEventFlagsClear(mbox->id, SYS_MBOX_FETCH_EVENT);
+
+    osKernelRestoreLock(state);
     return (us_ticker_read() - start) / 1000;
 }
 
@@ -232,10 +274,22 @@ u32_t sys_arch_mbox_fetch(sys_mbox_t *mbox, void **msg, u32_t timeout) {
  *                                  return ERR_OK.
  *---------------------------------------------------------------------------*/
 u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg) {
-    osStatus_t res = osMessageQueueGet(mbox->id, msg, NULL, 0);
-    if (res != osOK)
+    uint32_t flags = osEventFlagsWait(mbox->id, SYS_MBOX_FETCH_EVENT,
+            osFlagsWaitAny | osFlagsNoClear, 0);
+    if (!(flags & SYS_MBOX_FETCH_EVENT))
         return SYS_MBOX_EMPTY;
 
+    int state = osKernelLock();
+
+    if (msg)
+        *msg = mbox->queue[mbox->fetch_idx % MB_SIZE];
+    mbox->fetch_idx += 1;
+
+    osEventFlagsSet(mbox->id, SYS_MBOX_POST_EVENT);
+    if (mbox->post_idx == mbox->fetch_idx)
+        osEventFlagsClear(mbox->id, SYS_MBOX_FETCH_EVENT);
+
+    osKernelRestoreLock(state);
     return ERR_OK;
 }
 

features/FEATURE_LWIP/lwip-interface/lwip-sys/arch/sys_arch.h

@@ -47,15 +47,21 @@ typedef struct {
 #define MB_SIZE      8
 
 typedef struct {
-    osMessageQueueId_t   id;
-    osMessageQueueAttr_t attr;
-    char                 queue[MB_SIZE * (sizeof(void*) + sizeof(os_message_t))];
-    os_message_queue_t   data;
+    osEventFlagsId_t   id;
+    osEventFlagsAttr_t attr;
+    os_event_flags_t   data;
+
+    uint8_t     post_idx;
+    uint8_t     fetch_idx;
+    void*       queue[MB_SIZE];
 } sys_mbox_t;
 
+#define SYS_MBOX_FETCH_EVENT 0x1
+#define SYS_MBOX_POST_EVENT  0x2
+
 #define SYS_MBOX_NULL               ((uint32_t) NULL)
-#define sys_mbox_valid(x)           (((*x).id == NULL) ? 0 : 1 )
-#define sys_mbox_set_invalid(x)     ( (*x).id = NULL )
+#define sys_mbox_valid(x)           (((*x).id == NULL) ? 0 : 1)
+#define sys_mbox_set_invalid(x)     ( (*x).id = NULL)
 
 #if ((DEFAULT_RAW_RECVMBOX_SIZE) > (MB_SIZE)) || \
     ((DEFAULT_UDP_RECVMBOX_SIZE) > (MB_SIZE)) || \