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Improve documentation: Some words about multiple execution contexts in lwIP

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Dirk Ziegelmeier
2016-09-29 12:51:45 +02:00
parent 65796cd827
commit 682b82aad8
6 changed files with 66 additions and 6 deletions
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63
doc/doxygen/main_page.h
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@@ -1,4 +1,4 @@
/**
/**
* @defgroup lwip lwIP
*
* @defgroup infrastructure Infrastructure
@@ -7,7 +7,7 @@
* Non thread-safe APIs, callback style for maximum performance and minimum
* memory footprint.
*
* @defgroup threadsafe_api Thread-safe APIs
* @defgroup sequential_api Sequential-style APIs
* Thread-safe APIs, blocking functions. More overhead, but can be called
* from any thread except TCPIP thread.
*
@@ -31,6 +31,63 @@
* @verbinclude "contrib.txt"
*/
/**
* @page pitfalls Common pitfalls
*
* Multiple Execution Contexts in lwIP code
* ========================================
*
* The most common source of lwIP problems is to have multiple execution contexts
* inside the lwIP code.
*
* lwIP can be used in two basic modes: @ref lwip_nosys (no OS/RTOS
* running on target system) or @ref lwip_os (there is an OS running
* on the target system).
*
* Mainloop Mode
* -------------
* In mainloop mode, only @ref callbackstyle_api can be used.
* The user has two possibilities to ensure there is only one
* exection context at a time in lwIP:
*
* 1) Deliver RX ethernet packets directly in interrupt context to lwIP
* by calling netif->input directly in interrupt. This implies all lwIP
* callback functions are called in IRQ context, which may cause further
* problems in application code: IRQ is blocked for a long time, multiple
* execution contexts in application code etc. When the application wants
* to call lwIP, it only needs to disable interrupts during the call.
* If timers are involved, even more locking code is needed to lock out
* timer IRQ and ethernet IRQ from each other, assuming these may be nested.
*
* 2) Run lwIP in a mainloop. There is example code here: @ref lwip_nosys.
* lwIP is _ONLY_ called from mainloop callstacks here. The ethernet IRQ
* has to put received telegrams into a queue which is polled in the
* mainloop. Ensure lwIP is _NEVER_ called from an interrupt, e.g.
* some SPI IRQ wants to forward data to udp_send() or tcp_write()!
*
* OS Mode
* -------
* In OS mode, @ref callbackstyle_api AND @ref sequential_api can be used.
* @ref sequential_api are designed to be called from threads other than
* the TCPIP thread, so there is nothing to consider here.
* But @ref callbackstyle_api functions must _ONLY_ be called from
* TCPIP thread. It is a common error to call these from other threads
* or from IRQ contexts. ​Ethernet RX needs to deliver incoming packets
* in the correct way by sending a message to TCPIP thread, this is
* implemented in tcpip_input().​​
* Again, ensure lwIP is _NEVER_ called from an interrupt, e.g.
* some SPI IRQ wants to forward data to udp_send() or tcp_write()!
*
* 1) tcpip_callback() can be used get called back from TCPIP thread,
* it is safe to call any @ref callbackstyle_api from there.
*
* 2) Use @ref LWIP_TCPIP_CORE_LOCKING. All @ref callbackstyle_api
* functions can be called when lwIP core lock is aquired, see
* @ref LOCK_TCPIP_CORE() and @ref UNLOCK_TCPIP_CORE().
* These macros cannot be used in an interrupt context!
* Note the OS must correctly handle priority inversion for this.
*/
/**
* @page bugs Reporting bugs
* Please report bugs in the lwIP bug tracker at savannah.\n
@@ -60,7 +117,7 @@
* to use @ref LWIP_TCPIP_CORE_LOCKING.\n
* Porting: implement all functions in @ref sys_layer.\n
* You can use @ref callbackstyle_api together with @ref tcpip_callback,
* and all @ref threadsafe_api.
* and all @ref sequential_api.
*/
/**