Echelon LonTal Stack - Manual (Page 121)

LonTalk Stack Developer’s Guide 109
a pointer to the created semaphore and returns a status variable that indicates
whether the function was successful.
The LonTalk Stack includes source code for OSAL files that interface with
Windows and Linux. To use a different operating system or provide your own
operating system services, you must modify the OSAL files to implement the API
for that operating system.
For more information about the OSAL functions, see The Operating System
Abstraction Layer. For information about configuring the operating system, see
Configuring the Operating System.
Providing Persistent Storage for Non-Volatile Data
The LonTalk host stack provides an API for managing non-volatile data (NVD).
Because non-volatile data is stored and managed by the host processor rather
than the Echelon Smart Transceiver, the LonTalk Stack application must
implement the API’s functions so that both the LonTalk host stack and the
application can read and write NVD to non-volatile memory (typically, flash
memory). Two example implementations, one using a flash file system, and one
using raw flash access (through the HAL flash access routines) are provided in
the FtxlNvdFlashDirect.c and FtxlNvdFlashFs.c files.
The implementations of the NVD-management functions are contained in one of
the following files (all of which are copied to the project directory by the LonTalk
Interface Developer utility):
• FtxlNvdFlashDirect.c for direct-access flash memory management
• FtxlNvdFlashFs.c for file-system flash memory management
• FtxlNvdUserDefined.c for your own flash memory management
Typically, if you select either the direct flash model or the flash file system model,
you need only specify the appropriate value for the non-volatile root in the
LonTalk Interface Developer Utility. This section describes how the LonTalk API
uses the non-volatile memory driver, in case you need to implement your own
user-defined non-volatile data driver or modify one of the provided drivers.
Non-volatile data is stored in segments. Two of the segments are used to store
data maintained by the LonTalk host stack, and the third segment is used to
store data maintained by the application. Examples of data maintained by the
LonTalk host stack include network variable configuration and address tables.
Examples of data maintained by the application include configuration network
variable values and persistent memory files (used for configuration property
value files and user files). Each data segment is identified by an enumeration of
type LonNvdSegmentType, defined in the FtxlTypes.h file.
The LonTalk host stack reads non-volatile data (loads it into RAM) only during
device initialization. Included with the data is a header that the LonTalk host
stack uses for validation. Within this header is an application identifier,
generated by the LonTalk Interface Developer utility, that allows the LonTalk
host stack to ensure that the data belongs to the current application. The header
also includes a checksum to ensure that the data is free of errors. If any of these
validations fails, the LonTalk host stack deletes all non-volatile data in the
segment and sets the device to the unconfigured state.