FreeRTOS+TCP simulator on Linux 64bit requires ipconfigBUFFER_PADDING == 14

Libraries
1

The instructions for building and running the TCP echo demo on a Linux simulator target should probably mention that with a 64-bit host (which are now pretty much universal) you must set ipconfigBUFFER_PADDING to 14 in FreeRTOSIPConfig.h:

diff --git a/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/FreeRTOSIPConfig.h b/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/FreeRTOSIPConfig.h
index 82975dff5..ffffa90b4 100644
--- a/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/FreeRTOSIPConfig.h
+++ b/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/FreeRTOSIPConfig.h
@@ -301,6 +301,8 @@ disconnecting stage will timeout after a period of non-activity. */
 #define ipconfigTCP_KEEP_ALIVE                         ( 1 )
 #define ipconfigTCP_KEEP_ALIVE_INTERVAL                ( 20 ) /* in seconds */
 
+#define ipconfigBUFFER_PADDING 14
+
 #define portINLINE __inline
 
 #endif /* FREERTOS_IP_CONFIG_H */

Otherwise, the assert at line 1156 in FreeRTOS_IP.c will fail:

  1139  BaseType_t FreeRTOS_IPInit( const uint8_t ucIPAddress[ ipIP_ADDRESS_LENGTH_BYTES ],
  1140                              const uint8_t ucNetMask[ ipIP_ADDRESS_LENGTH_BYTES ],
  1141                              const uint8_t ucGatewayAddress[ ipIP_ADDRESS_LENGTH_BYTES ],
  1142                              const uint8_t ucDNSServerAddress[ ipIP_ADDRESS_LENGTH_BYTES ],
  1143                              const uint8_t ucMACAddress[ ipMAC_ADDRESS_LENGTH_BYTES ] )
  1144  {
  1145      BaseType_t xReturn = pdFALSE;
  [...]
  1151      
  1152      if( sizeof( uintptr_t ) == 8 )
  1153      {
  1154          /* This is a 64-bit platform, make sure there is enough space in
  1155           * pucEthernetBuffer to store a pointer. */
  1156          configASSERT( ipconfigBUFFER_PADDING == 14 );
  1157      }
  1158

Unfortunately, the default assert handler in the demo main.c just silently goes into an infinite loop, so it takes a fair bit of effort to figure out why the demo won’t run as-is. Therefore, I’d also suggest adding an fprintf() call in main.c. I also prefer an exit() call, but I can see that might not be what everybody would want:

diff --git a/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/main.c b/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/main.c
index 0cf0a0709..c12730511 100644
--- a/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/main.c
+++ b/FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Posix/main.c
@@ -247,10 +247,8 @@ volatile uint32_t ulSetToNonZeroInDebuggerToContinue = 0;
     /* Called if an assertion passed to configASSERT() fails.  See
     http://www.freertos.org/a00110.html#configASSERT for more information. */
 
-    /* Parameters are not used. */
-    ( void ) ulLine;
-    ( void ) pcFileName;
-
+    fprintf(stderr,"assert failed %s line %lu\n", pcFileName, ulLine);
+    exit(1);
 
     taskENTER_CRITICAL();
     {
2

Thank you for sharing your feedback. I agree adding more logs here will be useful in this case and we will update the demos.

3

Yes, thanks for reporting this. That will save time for other developers when they get stuck in vAssertCalled().
I just created PR #598 for this: “Let vAssertCalled() produce some logging to stdout”

About the configASSERT: we could also turn it into a static compiler check:

#if UINTPTR_MAX == 0xffffffffffffffff
{
    /* This is a 64-bit platform, make sure there is enough space in
     * pucEthernetBuffer to store a pointer. */
    #if( ipconfigBUFFER_PADDING < 14 )
        #error On a 64-bit platform, `ipconfigBUFFER_PADDING` must be greater than or equal to 14
    #endif
}
#endif

but I am not sure if all compilers will like this construction.

Currently the test is ipconfigBUFFER_PADDING == 14, but in fact a higher value may also be used (18, 22, 26 etc).

4

Thanks, @htibosch for that PR! We are working on getting it merged in the mainline.

And @Grant_Edwards yes, I think we should add that detail to the documentation. Apologies for your trouble.

Can we add a conditional value of ipconfigBUFFER_PADDING in the FreeRTOSIPConfig.h source file for the POSIX demo like so:

/* Some compilers might not like this, but this is for Posix simulator only.  */
#if UINTPTR_MAX == 0xffffffffffffffff
{
    #define ipconfigBUFFER_PADDING 14
}
/* else let the default value take over. */

This would save so much time for people trying to get started with the Posix demo. What do you all think?