@c @c COPYRIGHT (c) 1988-1999. @c On-Line Applications Research Corporation (OAR). @c All rights reserved. @c @c $Id$ @c @chapter Non-Volatile Memory Driver The Non-Volatile driver is responsible for providing an interface to various types of non-volatile memory. These types of memory include, but are not limited to, Flash, EEPROM, and battery backed RAM. The capabilities provided by this class of device driver are: @itemize @bullet @item Initialize the Non-Volatile Memory Driver @item Optional Disable Read and Write Handlers @item Open a Particular Memory Partition @item Close a Particular Memory Partition @item Read from a Particular Memory Partition @item Write to a Particular Memory Partition @item Erase the Non-Volatile Memory Area @end itemize There is currently only one non-volatile device driver included in the RTEMS source tree and it does not adhere to this device driver model. The information provided in this chapter is based on drivers developed by OAR Corporation personnel for applications using RTEMS. It is hoped that this driver model information can form the basis for a standard non-volatile memory driver model that can be supported in future RTEMS distribution. @section Major and Minor Numbers The @b{major} number of a device driver is its index in the RTEMS Device Address Table. A @b{minor} number is associated with each device instance managed by a particular device driver. An RTEMS minor number is an @code{unsigned32} entity. Convention calls dividing the bits in the minor number down into categories that specify an area of non-volatile memory and a partition with that area. This results in categories like the following: @itemize @bullet @item @b{area} - indicates a block of non-volatile memory @item @b{partition} - indicates a particular address range with an area @end itemize From the above, it should be clear that a single device driver can support multiple types of non-volatile memory in a single system. The minor number is used to distinguish the types of memory and blocks of memory used for different purposes. @section Non-Volatile Memory Driver Configuration There is not a standard non-volatile driver configuration table but some fields are common across different drivers. The non-volatile memory driver configuration table is typically an array of structures with each structure containing the information for a particular area of non-volatile memory. The following is a list of the type of information normally required to configure each area of non-volatile memory. @table @b @item memory_type is the type of memory device in this area. Choices are battery backed RAM, EEPROM, Flash, or an optional user-supplied type. If the user-supplied type is configured, then the user is responsible for providing a set of routines to program the memory. @item memory is the base address of this memory area. @item attributes is a pointer to a memory type specific attribute block. Some of the fields commonly contained in this memory type specific attribute structure area: @table @b @item use_protection_algorithm is set to TRUE to indicate that the protection (i.e. locking) algorithm should be used for this area of non-volatile memory. A particular type of non-volatile memory may not have a protection algorithm. @item access is an enumerated type to indicate the organization of the memory devices in this memory area. The following is a list of the access types supported by the current driver implementation: @itemize @bullet @item simple unsigned8 @item simple unsigned16 @item simple unsigned32 @item simple unsigned64 @item single unsigned8 at offset 0 in an unsigned16 @item single unsigned8 at offset 1 in an unsigned16 @item single unsigned8 at offset 0 in an unsigned32 @item single unsigned8 at offset 1 in an unsigned32 @item single unsigned8 at offset 2 in an unsigned32 @item single unsigned8 at offset 3 in an unsigned32 @end itemize @item depth is the depth of the progamming FIFO on this particular chip. Some chips, particularly EEPROMs, have the same programming algorithm but vary in the depth of the amount of data that can be programmed in a single block. @end table @item number_of_partitions is the number of logical partitions within this area. @item Partitions is the address of the table that contains an entry to describe each partition in this area. Fields within each element of this table are defined as follows: @table @b @item offset is the offset of this partition from the base address of this area. @item length is the length of this partition. @end table @end table By dividing an area of memory into multiple partitions, it is possible to easily divide the non-volatile memory for different purposes. @section Initialize the Non-Volatile Memory Driver At system initialization, the non-volatile memory driver's initialization entry point will be invoked. As part of initialization, the driver will perform whatever initializatin is required on each non-volatile memory area. The discrete I/O driver may register device names for memory partitions of particular interest to the system. Normally this will be restricted to the device "/dev/nv_memory" to indicate the entire device driver. @section Disable Read and Write Handlers Depending on the target's non-volatile memory configuration, it may be possible to write to a status register and make the memory area completely inaccessible. This is target dependent and beyond the standard capabilities of any memory type. The user has the optional capability to provide handlers to disable and enable access to a partiticular memory area. @section Open a Particular Memory Partition This is the driver open call. Usually this call does nothing other than validate the minor number. With some drivers, it may be necessary to allocate memory when a particular device is opened. If that is the case, then this is often the place to do this operation. @section Close a Particular Memory Partition This is the driver close call. Usually this call does nothing. With some drivers, it may be necessary to allocate memory when a particular device is opened. If that is the case, then this is the place where that memory should be deallocated. @section Read from a Particular Memory Partition This corresponds to the driver read call. After validating the minor number and arguments, this call enables reads from the specified memory area by invoking the user supplied "enable reads handler" and then reads the indicated memory area. When invoked the @code{argument_block} is actually a pointer to the following structure type: @example @group typedef struct @{ rtems_unsigned32 offset; void *buffer; rtems_unsigned32 length; rtems_unsigned32 status; @} Non_volatile_memory_Driver_arguments; @end group @end example The driver reads @code{length} bytes starting at @code{offset} into the partition and places them at @code{buffer}. The result is returned in @code{status}. After the read operation is complete, the user supplied "disable reads handler" is invoked to protect the memory area again. @section Write to a Particular Memory Partition This corresponds to the driver write call. After validating the minor number and arguments, this call enables writes to the specified memory area by invoking the "enable writes handler", then unprotecting the memory area, and finally actually writing to the indicated memory area. When invoked the @code{argument_block} is actually a pointer to the following structure type: @example @group typedef struct @{ rtems_unsigned32 offset; void *buffer; rtems_unsigned32 length; rtems_unsigned32 status; @} Non_volatile_memory_Driver_arguments; @end group @end example The driver writes @code{length} bytes from @code{buffer} and writes them to the non-volatile memory starting at @code{offset} into the partition. The result is returned in @code{status}. After the write operation is complete, the "disable writes handler" is invoked to protect the memory area again. @section Erase the Non-Volatile Memory Area This is one of the IOCTL functions supported by the I/O control device driver entry point. When this IOCTL function is invoked, the specified area of non-volatile memory is erased.