Changes between Version 6 and Version 7 of DsxDocumentation

Timestamp:

Jan 28, 2008, 12:21:28 AM (16 years ago)

Author:

alain

Comment:

--

DsxDocumentation

@@ -24 +24 @@
  * The coarse grain parallelism of the software application must be statically defined as  a '''Task & Communications Graph (TCG)'''. The number of tasks, and the communication channels between tasks should not change during execution. 
  * The software tasks are supposed to be written in C or C++, but - for portability reasons - the tasks must use an abstract '''System Resource Layer (SRL)''' API to access the communication and synchronizations resources. 
- * Each task in the TCG can be implemented as a ''software task'' (software running on an embedded processor), or can be implemented as an ''hardware task'', (running as a dedicated hardware coprocessor).
- * DSX allows the programmer to use unprotected shared memory spaces, but the prefered inter-tasks communication mechanism use the MWMR middleware. The MWMR (Multi-Writer, Multi-Reader) channels, are implemented as software FIFOs and can be shared by ''software tasks'', and by ''hardware tasks.
+ * Each task in the TCG can be implemented as a '''software task''' (software running on an embedded processor), or can be implemented as an '''hardware task''', (running as a dedicated hardware coprocessor).
+ * DSX allows the programmer to use unprotected shared memory spaces, but the prefered inter-tasks communication mechanism use the '''MWMR middleware'''. The MWMR (Multi-Writer, Multi-Reader) channels, are implemented as software FIFOs and can be shared by ''software tasks'', and by ''hardware tasks''.
  * DSX provides classical synchronization mechanisms such as barriers and locks, but inter-task synchronisation is mainly done through the data availability in the MWMR channels.
  * The target hardware architecture is a shared memory multi-processor system on chip (MP-SoC) using the SoCLib library of IP cores. But - in order to validate the multi-threaded software application - DSX is able to generate an executable binary code for a standard POSIX workstation.
@@ -83 +83 @@
 == C)  Defining the software application ==
 
-This chapter describes the DSX/L constructs used to define the Task & Communication Graph structure.
+This chapter describes the DSX/L syntax used to define the Task & Communication Graph structure.
 The TCG is a bipartite graph: the two types of nodes are the tasks and the communication channels.
-The following figure describes the TCG corresponding to an MJPEG decoder application. The two TG & RAMDAC tasks will be implemented as hardware coprocessors : the TG component implements a wire-less receiver, and the RAMDAC component is a graphic display controller. The 5 other tasks can be implemented as ''software tasks'' or  
-as ''hardware tasks''. In this example, all MWMR communication channels have one single producer, and one
+
+As an example, the following figure describes the TCG corresponding to an MJPEG decoder application. 
+The two TG & RAMDAC tasks will be implemented as hardware coprocessors : the TG component implements a wire-less receiver for the MJPEG stream, and the RAMDAC component is a graphic display controller. 
+The 5 other tasks can be implemented as ''software tasks'' or  as ''hardware tasks''. In this particular example, 
+all MWMR communication channels have one single producer, and one
 single consumer, which is frequent for stream oriented multi-media applications.
 
@@ -93 +96 @@
 As a software application can instanciate several instances of the same task, we must distinguish the task, and the task model. A task model defines the code associated to the task, and the task interface (corresponding to the system resources used by the task : MWMR communications channels, synchronization barriers, locks, and memspaces).
 {{{
-Task_model = Task( 'model_name',
+Task_Model = TaskModel( 'model_name',
                     infifos = [ 'inport_name', ... ] ,
                     outfifos = [ 'outport_name', ... ] ,
@@ -102 +105 @@
                     impls = [ SwTask( 'func', stack_size = 1024 , sources = [ 'func.c' ] )
 }}}   
-I a task does not use a given type of resource, the corresponding parameter can be skipped.
+If a task does not use a given type of resource, the corresponding parameter can be skipped.
 
 === C2) MWMR communication channel definition ===
 
+A MWMR communication channel is a memory buffer handled as a software FIFO that can have several producers and several consumers. Each channel is protected by an implicit lock for exclusive access. Any MWMR transaction 
+can be decomposed in five memory access:
+ 1.  get the lock protecting the MWMR (READ access).  
+ 1.  test the status of the MWMR (READ access).
+ 1.  transfer a burst of data between a local buffer and the MWMR (READ/WRITE access). 
+ 1.  update the status of the MWMR (WRITE access). 
+ 1.  release the lock (WRITE access).
+
+Any data transfer to or from a MWMR channel mut be an integer number of items. The item width is an
+intrinsic property of the channel. It is defined as a number of bytes, and it defines the channel ''width''.
+The channel ''depth'' is a number of items, and defines the total channel capacity.
+For performances reasons the channel ''width'' itself must be a multiple of 4 bytes.
+{{{  
+My_Channel = Mwmr( 'channel_name', width, depth )
+}}}
+In the mapping section of the DSX/L program, the 4 following software objects must be placed :
+ 1. ''desc'' :  read only informations regarding the communication channel
+ 1. ''status'' : channel state (number of stored items, read & write pointers)
+ 1. ''buffer'' : channel buffer containing the data
+ 1. ''lock'' : lock protecting exclusive access
+
 === C3) Synchronization barrier definition ===
 
-=== C4) Synchronization lock definition ===
-
-=== C5) Signal definition ===
-
-=== C6) Task instanciation ===
+The synchronization barriers can be used when the synchronization through the data availability in
+the MWMR communication channels in not enough. The set of tasks that are linked to a given barrier
+is defined when the the tasks are intanciated. Exclusive access to the barrier is protected by an implicit lock.
+{{{
+My_Barrier = Barrier( 'barrier_name' )
+}}}
+In the mapping section of the DSX/L program, the 3 following software objects must be placed :
+ 1. ''desc'' : read only informations regarding the synchronization barrier
+ 1. ''status'' : barrier state
+ 1. ''lock'' : lock protecting exclusive access
+
+=== C4) Memspace definition
+
+Direct communication through shared memory buffers is supported by DSX, but there is no protection mechanism, and the synchronization is the programmer responsability.
+A shared memory space is defined by two parameters : ''memspace_name'' is the name, and ''size'' defines
+the number of bytes to be reserved.
+{{{
+My_Shared_Buffer = Memspave( ''memspace_name', size )
+}}}
+In the mapping section of the DSX/L program, the 2 following software objects must be placed :
+ 1. ''desc'' : read only informations regarding the memspace
+ 1. ''mem'' : the shared memory buffer
+
+=== C5) lock definition ===
+
+A lock is a variable that can be used to protect exclusive access to a shared resource such as a shared
+memory space. It is implemented as a spinlock : the ''srl_lock_lock()'' funtion returns only when the lock
+has been obtained.
+{{{
+My_Lock = Lock( 'lock_name' )
+}}}
+In the mapping section of the DSX/L program, the lock can be explicitely placed in the memory space. 
+
+=== C6) Signal definition ===
+
+The DSX signals are used to signal a special event that is not synchronized with the data. The signal is transmitted
+to all registered tasks. The tasks are interrupted to execute the corresponding signal handler. Signals are mainlly
+used to implement soft real time constraints, a task can receive a signal, but cannot send a signal.
+{{{
+My_signal = Signal( 'signal_name' )
+}}}
+There is nothing to place in the mapping section.
+
+=== C7) Task instanciation ===
+
+A task is an instance of a task model. The constructor arguments are the task name ''task_name'', the task model
+''Task_Model'' (created by the TaskModel() function), a list of resources (MWMR channels, synchronization barriers,
+locks or memspaces), and the list of the signals that can be received by the task . DSX performs type checking between the port name and the associated resource.
+{{{
+My_Task = Task( 'task_name',
+                              Task_Model ,
+                             { 'port_name' : My_Channel, 'barrier_name' : My_Barrier, ... } ,
+                             { 'signal_name : My_signal, ... } )
+}}}
+In the mapping section of the DSX/L program, 4 software objects must be placed :
+ 1. ''desc'' : read-only informations associated to the task 
+ 1. ''status'' : state of the task
+ 1. ''stack'' : execution stack
+ 1. ''run'' : processor running the task
+
+A task that has real time constraints must be instanciated by a special constructor. 
+There is two extra arguments : ''cond_activate'' is the signal definig the activation condition, and ''cond_deadline''
+is the signal defining the dead_line condition. 
+{{{
+My_RT_Task = RtTask( 'task_name',
+                              Task_Model ,
+                             { 'port_name' : My_Channel, 'barrier_name' : My_Barrier, ... } ,
+                             { 'signal_name : My_signal, ... } ,
+                             cond_activate ,
+                             cond_deadline )
+}}}
+
 == D)  Defining the hardware architecture ==