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If the call was successful and the message was posted to the task’s message queue.
OS_ERR_INT_Q_FULL
If OS_CFG_ISR_POST_DEFERRED_EN is to DEF_ENABLED in os_cfg.h: If the deferred interrupt post queue is full.
OS_ERR_MSG_POOL_EMPTY
If running out of OS_MSG to hold the message being posted.
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