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  2. <html><head><meta content="text/html; charset=ISO-8859-1" http-equiv="content-type"><title>PTE on DSP/BIOS</title></head><body><br><big><big><big><span style="font-weight: bold;">PTE on DSP/BIOS</span></big></big></big><meta http-equiv="CONTENT-TYPE" content="text/html; charset=utf-8"><title></title><meta name="GENERATOR" content="OpenOffice.org 2.3  (Linux)">
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  19. 

  20. <p style="margin-bottom: 0in;"><br>
    21. 

  21. </p>
    22. 

  22. <p style="margin-bottom: 0in;">The DSP/BIOS OSAL is relatively
    23. 

  23. straightforward and maps relatively cleanly to the DSP/BIOS API.  For
    24. 

  24. instance, most mutex and semaphore operations are supported directly
    25. 

  25. using the LCK and SEM API's.  Specific details and exceptions are
    26. 

  26. described below.</p>
    27. 

  27. <h1 class="western">Threads</h1>
    28. 

  28. <h2 class="western">Thread creation</h2>
    29. 

  29. <p>OsThreadCreate allocates a dspbiosThreadData structure that
    30. 

  30. contains semaphores used for joining to a thread, cancelling a thread
    31. 

  31. and the initial priority requested by the user.  A pointer to this
    32. 

  32. structure is stored as a TLS value.  
    33. 

  33. </p>
    34. 

  34. <p>OsThreadCreate must create threads in a suspended state.  In
    35. 

  35. DSP/BIOS this is done by setting the initial priority to zero.  The
    36. 

  36. initial priority is stored in the per thread control data.  When
    37. 

  37. OsThreadStart is called, it retrieves the initial priority from the
    38. 

  38. control data attached to the thread and then sets the priority of the
    39. 

  39. thread, which starts execution.</p>
    40. 

  40. <h2 class="western">Thread termination</h2>
    41. 

  41. <p>In order for pthread_join to wait for a thread, OsThreadWaitForEnd
    42. 

  42. is called.   Since DSP/BIOS doesn't have a explicit system call for
    43. 

  43. this, we emulate it using a semaphore that is posted to when the
    44. 

  44. thread exits.  This semaphore is saved in the per thread control
    45. 

  45. structure.</p>
    46. 

  46. <h2 class="western">Thread cleanup</h2>
    47. 

  47. <p style="margin-bottom: 0in;"><br>
    48. 

  48. </p>
    49. 

  49. <p style="margin-bottom: 0in;">The PTE library calls <font face="Courier New, monospace">OsThreadDelete</font>
    50. 

  50. to signal to the OSAL that the resources for a task can be freed. 
    51. 

  51. For DSP/BIOS, this means a call to TSK_delete (task resources are <i>not</i><span style="font-style: normal;">
    52. 

  52. automatically freed by DSP/BIOS when the thread exits).</span></p>
    53. 

  53. <p style="margin-bottom: 0in; font-style: normal;"><br>
    54. 

  54. </p>
    55. 

  55. <p style="margin-bottom: 0in;"><font face="Courier New, monospace"><span style="font-style: normal;">OsThreadDelete</span></font><span style="font-style: normal;">
    56. 

  56. will be called at a number of points.  For attached threads, it will
    57. 

  57. be called when </span><font face="Courier New, monospace"><span style="font-style: normal;">pthread_join</span></font><span style="font-style: normal;">
    58. 

  58. is called and returns or when </span><font face="Courier New, monospace"><span style="font-style: normal;">pthread_detach</span></font><span style="font-style: normal;">
    59. 

  59. is called for a terminated thread.  For detached threads
    60. 

  60. </span><font face="Courier New, monospace"><span style="font-style: normal;">OsThreadDelete</span></font><span style="font-style: normal;">
    61. 

  61. will be called when the thread exits.</span></p>
    62. 

  62. <p style="margin-bottom: 0in; font-style: normal;"><br>
    63. 

  63. </p>
    64. 

  64. <p style="margin-bottom: 0in;"><span style="font-style: normal;">The
    65. 

  65. problem is that </span><font face="Courier New, monospace"><span style="font-style: normal;">TSK_delete</span></font><span style="font-style: normal;">
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  66. naturally can not be called from the same context as the thread that
    67. 

  67. we're trying to free.  For the first two cases (</span><font face="Courier New, monospace"><span style="font-style: normal;">pthread_join</span></font><span style="font-style: normal;">
    68. 

  68. and </span><font face="Courier New, monospace"><span style="font-style: normal;">pthread_detach</span></font><span style="font-style: normal;">)
    69. 

  69. this is not a problem as these will always be called from another
    70. 

  70. thread.  However, for detached threads </span><font face="Courier New, monospace"><span style="font-style: normal;">OsThreadDelete</span></font><span style="font-style: normal;">
    71. 

  71. will be called from the same context.</span></p>
    72. 

  72. <p style="margin-bottom: 0in; font-style: normal;"><br>
    73. 

  73. </p>
    74. 

  74. <p style="margin-bottom: 0in;"><span style="font-style: normal;">To
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  75. work around it, the DSP/BIOS OSAL includes a low priority that will
    76. 

  76. clean up detached threads.  If </span><font face="Courier New, monospace"><span style="font-style: normal;">OsThreadDelete</span></font><span style="font-style: normal;">
    77. 

  77. detects that it is being called from the same context, it will post a
    78. 

  78. message to a mailbox that the garbage collector thread is waiting on.
    79. 

  79.  The garbage collector thread will then call </span><font face="Courier New, monospace"><span style="font-style: normal;">TSK_delete</span></font><span style="font-style: normal;">
    80. 

  80. for that thread, as well as to clean up any resources that were
    81. 

  81. allocated when the thread was created.</span></p>
    82. 

  82. <p style="margin-bottom: 0in;"><br>
    83. 

  83. </p>
    84. 

  84. <h1 class="western">Thread Local Storage</h1>
    85. 

  85. <p style="margin-bottom: 0in;"><br>
    86. 

  86. </p>
    87. 

  87. <p style="margin-bottom: 0in;">TLS is implemented using the
    88. 

  88. &#8220;environment&#8221; of DSP/BIOS threads.  This allows a single value to
    89. 

  89. be associated with a thread.  The TLS helper routines are used to
    90. 

  90. provide full TLS functionality; these routines allocate a structure
    91. 

  91. that holds multiple TLS keys and values.  The DSP/BIOS environment is
    92. 

  92. used to hold a pointer to this structure.</p>
    93. 

  93. <p style="margin-bottom: 0in;"><br>
    94. 

  94. </p>
    95. 

  95. <h1 class="western">Thread Cancellation</h1>
    96. 

  96. <p style="margin-bottom: 0in;"><br>
    97. 

  97. </p>
    98. 

  98. <p style="margin-bottom: 0in;">Since DSP/BIOS does not natively
    99. 

  99. provide a way to break out of blocked operations, this functionality
    100. 

  100. is emulated using a cancellation semaphore that is stored in the per
    101. 

  101. thread control data.  When the user requests that a thread be
    102. 

  102. canceled (i.e. <font face="Courier New, monospace">OsThreadCancel</font>
    103. 

  103. is called) this semaphore is posted to.  In
    104. 

  104. <font face="Courier New, monospace">OsSemaphoreCancellablePend</font>,
    105. 

  105. the cancellation semaphore as well as the user semaphore are polled
    106. 

  106. (rather than blocking) and the routine returns if the cancellation
    107. 

  107. semaphore is posted to.</p>
    108. 

  108. </body></html>
    109.