Echelon Neuron C - Manual (Page 56)

36 Compiler Directives
#pragma specify_io_clock string
Specify this directive to inform the compiler of the value of the Neuron clock
speed (external crystal frequency for Series 3100 devices, or the I/O clock
frequency for Series 5000 devices).
The directive is generally not required for Series 5000 chips because the I/O
clock frequency is fixed for those chips.
This directive is only useful in combination with the sci I/O model, and
permits the compiler to calculate the register settings for the SCI I/O
hardware in any Neuron Chip or Smart Transceiver equipped with SCI I/O
hardware. The clock rate is specified with a string constant following the
pragma name as shown. The only clock rates that may be used with SCI I/O
hardware are “20 MHz”, “10 MHz”, “6.5536 MHz”, “5 MHz”, and “2.5 MHz”.
The strings must appear exactly as shown, including capitalization.
This directive is not supported in model files.
#pragma system_image_extensions nv_length_override
This directive enables the NV length override system image extension. This
system image extension is used to implement changeable network variable
types. You must provide an extension function named
get_nv_length_override() as detailed below. Using this compiler directive
together with a version of the Neuron firmware that does not support system
extensions will cause a linker error (NLD#477).
You can continue to access the nv_len property as discussed in the Neuron C
Programmer’s Guide . However, the Neuron C Version 2.1 (and later) system
image extension technique provides a more robust implementation and
should therefore be used for all new designs.
Where #pragma system_image_extensions nv_length_override enables the
nv_length_override system image extension, you must also provide the
system extension. To do so, you must implement a function that meets the
following prototype:
unsigned get_nv_length_override(unsigned nvIndex);
The function returns the current length in bytes of the network variable with
the given index, or 0xFF to signal that the length has not been changed. You
must maintain information about the current length (and type) for network
variables with changeable types in some appropriate, persistent, variable.
You can use the sizeof( ) operator to obtain the initial size of the network
variable. See the discussion on
Changeable Type Network Variables in the
chapter How Devices Communicate Using Network Variables of the Neuron
C Programmer's Guide for more information.
This directive is not supported in model files.
#pragma transaction_by_address_off
#pragma transaction_by_address_on
These pragmas explicitly control which version of transaction ID allocation
algorithm the Neuron firmware uses. Some versions of the Neuron firmware
support a new version of transaction ID allocation that has superior duplicate
rejection properties. For the Neuron 3150 Chip, 3150 Smart Transceiver,