If the target platform resources allow then the first step in
debugging should be to enable
inclusion of assert checking will increase the code footprint and
lower the performance, but does allow the code to catch internal
errors from unexpected data values. e.g. when the application/client
is not able to guarantee the validity of data passed into the MODBUS
The MODBUS asserts are controlled via the standard eCos Infrastructure CYGPKG_INFRA package CYGDBG_USE_ASSERTS option. If enabled then run-time assertion checks are performed by the MODBUS package.
If assertions are enabled, and a debugger is being used it is normally
worthwhile setting a breakpoint at start-up on
cyg_assert_fail symbol, so that the debugger
will stop prior to entering the default busy-loop assert processing.
In conjuction with the CYGDBG_MODBUS_DEBUG CDL configuration setting and sub-options, the header-file src/modbus_diag.h implements the MODBUS specific debug control.
When CYGDBG_MODBUS_DEBUG is enabled a set of individually selectable sub-systems are available to control the diagnostic output generated.
However, when developing or debugging the MODBUS implementation it may be simpler (with less build side-effects) to control the debugging output via direct uncommenting of the necessary manifests at the head of the src/modbus_diag.h source file, than re-configuring the complete eCos configuration via the CDL. That way only the MODBUS package will be re-built.
Note: Some diagnostic output if enabled may adversely affect the operation of the MODBUS support as seen by 3rd-party code. For example, “slow” serial diagnostic output of the packet parsing and response generation could mean that a significant amount of time passes, such that the MODBUS support no longer adheres to the timeout limits imposed by external code.