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<h1>Target Communication Framework Services - Registers</h1>

<ul>
    <li><a href='#VersionHistory'>Version History</a>
    <li><a href='#Overview'>Overview</a>
    <li><a href='#Cmds'>Commands</a>
    <ul>
        <li><a href='#CmdGetContext'>Get Context</a>
        <li><a href='#CmdGetChildren'>Get Children</a>
        <li><a href='#CmdSetRegister'>Set Register</a>
        <li><a href='#CmdGetRegister'>Get Register</a>
        <li><a href='#CmdSetMultiple'>Set Multiple Registers</a>
        <li><a href='#CmdGetMultiple'>Get Multiple Registers</a>
        <li><a href='#CmdSearch'>Search for Registers</a>
    </ul>
    <li><a href='#Events'>Events</a>
    <li><a href='#API'>API</a>
</ul>

<h1>Registers Service</h1>

<h2><a name='VersionHistory'>Version History</a></h2>

<table border=1 cellpadding=8>
    <tr>
        <th>Version
        <th>Date
        <th>Change
    <tr>
        <td>0.1
        <td>2008-01-10
        <td>Initial contribution
    <tr>
        <td>0.2
        <td>2008-04-23
        <td>Added get/set multiple
    <tr>
        <td>1.0
        <td>2008-05-06
        <td>Approved
    <tr>
        <td>1.1
        <td>2009-03-16
        <td>Added search command and several context properties
</table>

<h2><a name='Overview'>Overview</a></h2>

<p>The service provides basic operations to read/write CPU and hardware registers. Command
and event parameters are encoded as zero terminated <a href='TCF Specification.html#JSON'>JSON</a> strings.</p>

<p>The service uses standard format for error reports,
see <a href='TCF Services.html#ErrorFormat'>Error Report Format</a>.</p>

In addition to commands that can set/get individual register context values, the service defines commands to set/get values at
multiple locations. This allows:
<ol>
    <li> to get/set multiple register contexts in one command
    <li> to specify offset and size for get/set on large register groups
    <li> to get/set truncated register values, e.g. only the low 32 bits of a 64-bit register
</ol>

<h2><a name='Cmds'>Commands</a></h2>

<h3><a name='CmdGetContext'>Get Context</a></h3>

<pre><b><font face="Courier New" size=2 color=#333399>
C &bull; <i>&lt;token&gt;</i> &bull; Registers &bull; getContext &bull; <i>&lt;string: context ID&gt;</i> &bull;
</font></b></pre>

<p>The command retrieves context info for given context ID. A context corresponds to an
register, register group, register bit field, etc. Exact meaning of a context depends on the target.
Target agent should define contexts hierarchy that is:</p>

<ul type='disc'>
    <li>Adequately reflects target hardware registers layout;
    <li>Consistent with the lingo/terminology of the processor manuals;
    <li>Intuitive to a user.
</ul>

<p>Reply:</p>

<pre><b><font face="Courier New" size=2 color=#333399>
R &bull; <i>&lt;token&gt;</i> &bull; <i>&lt;error report&gt;</i> &bull; <i>&lt;context data&gt;</i> &bull;

<i>&lt;context data&gt;</i>
    &rArr; null
    &rArr; <i>&lt;object&gt;</i>
</font></b></pre>

<p>Context data object should, at least, contain member
<b><font face="Courier New" size=2 color=#333399>"ID" : <i>&lt;string&gt;.</i></font></b>
Context data is expected to be cached by clients.
Service sends contextChanged event to notify changes in context data.</p>

<p>Predefined register context properties are:</p>
<ul>
    <li><code><b><font face="Courier New" size=2 color=#333399>"ID" : <i>&lt;string&gt;</i></font></b></code>
    - ID of the context, same as getContext command argument.

    <li><code><b><font face="Courier New" size=2 color=#333399>"ParentID" : <i>&lt;string&gt;</i></font></b></code>
    - ID of a parent context.

    <li><code><b><font face="Courier New" size=2 color=#333399>"ProcessID" : <i>&lt;string&gt;</i></font></b></code>
    - process ID.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Name" : <i>&lt;string&gt;</i></font></b></code>
    - context name.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Description" : <i>&lt;string&gt;</i></font></b></code>
    - context description.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Size" : <i>&lt;int&gt;</i></font></b></code>
    - context size in bytes. Byte arrays in get/set commands should be same size.
    Hardware register can be smaller then this size, for example in case
    when register size is not an even number of bytes. In such case implementation
    should add/remove padding that consists of necessary number of zero bits.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Readable" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if context value can be read.

    <li><code><b><font face="Courier New" size=2 color=#333399>"ReadOnce" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if reading the context (register) destroys its current value - it can be read only once.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Writeable" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if context value can be written.

    <li><code><b><font face="Courier New" size=2 color=#333399>"WriteOnce" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if register value can not be overwritten - every write counts.

    <li><code><b><font face="Courier New" size=2 color=#333399>"SideEffects" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if writing the context can change values of other registers.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Volatile" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if the register value can change even when target is stopped.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Float" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if the register value is a floating-point value.

    <li><code><b><font face="Courier New" size=2 color=#333399>"BigEndian" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if big endian, which means decreasing numeric significance with increasing bit number.
    If absent default if false, which implies little endianess. The endianess is used to encode and decode values of get, getm, set and setm commands.

    <li><code><b><font face="Courier New" size=2 color=#333399>"LeftToRight" : <i>&lt;boolean&gt;</i></font></b></code>
    - true if the lowest numbered bit (i.e. bit #0 or bit #1, depending on "FirstBit" value) should be shown to user as the left-most bit.

    <li><code><b><font face="Courier New" size=2 color=#333399>"FirstBit" : <i>&lt;int&gt;</i></font></b></code>
    - 0 or 1. If the context has bit field children, bit positions of the fields can be zero-based or 1-based.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Bits" : <i>&lt;array of int&gt;</i></font></b></code>
    - if context is a bit field, contains the field bit numbers in the parent context.

    <li><code><b><font face="Courier New" size=2 color=#333399>"Values" : <i>&lt;array of named values&gt;</i></font></b></code>
    - predefined names (mnemonics) for some of context values.
        <pre><b><font face="Courier New" size=2 color=#333399>
        <i>&lt;array of named values&gt;</i>
                &rArr; null
                &rArr; [ ]
                &rArr; [ <i>&lt;named values list&gt;</i> ]

        <i>&lt;named values list&gt;</i>
                &rArr; <i>&lt;object: named value properties&gt;</i>
                &rArr; <i>&lt;named values list&gt;</i> , <i>&lt;object: named value properties&gt;</i>
        </font></b></pre>
    Named value properties are:
    <ul>
        <li><code><b><font face="Courier New" size="2" color="#333399">"Name"</font></b></code>
        - Name (menemonic) of the value.
        <li><code><b><font face="Courier New" size="2" color="#333399">"Value"</font></b></code>
        - BASE64 encoded binary bits of the value.
        <li><code><b><font face="Courier New" size="2" color="#333399">"Description"</font></b></code>
        - Short, human readable description of the value.
        </ul>
        <p>

    <li><code><b><font face="Courier New" size="2" color="#333399">"MemoryAddress" : <i>&lt;int&gt;</i></font></b></code>
    - The address of a memory mapped register. If MemoryContext is provided, the address is referring into that context.

    <li><code><b><font face="Courier New" size="2" color="#333399">"MemoryContext" : <i>&lt;string&gt;</i></font></b></code>
    - The context ID of a memory context in which a memory mapped register is located. Used together with MemoryAddress to inform where in memory memory mapped registers are located.
      If absent and MemoryAddress is defined, the context ID of this context is used as default.

    <li><code><b><font face="Courier New" size="2" color="#333399">"CanSearch" : <i>&lt;array of strings&gt;</i></font></b></code>
    - A list of attribute names which can be searched for starting on this context.
      If absent the context does not support search.

    <li><code><b><font face="Courier New" size="2" color="#333399">"Role" : <i>&lt;string&gt;</i></font></b></code>
    - The role the register plays in a program execution.

    <p>Predefined register role strings are:</p>
    <ul>
        <li><code><b><font face="Courier New" size="2" color="#333399">"PC"</font></b></code>
        - Program counter. Defines instruction to execute next.

        <li><code><b><font face="Courier New" size="2" color="#333399">"SP"</font></b></code>
        - Register defining the current stack pointer location.

        <li><code><b><font face="Courier New" size="2" color="#333399">"FP"</font></b></code>
        - Register defining the current frame pointer location.

        <li><code><b><font face="Courier New" size="2" color="#333399">"RET"</font></b></code>
        - Register used to store the return address for calls.

        <li><code><b><font face="Courier New" size="2" color="#333399">"CORE"</font></b></code>
        - Indicates register or register groups which belong to the core state.
          Commonly set for general purpose registers,
          condition code and other registers which are of special
          interest for determining the state.
   </ul>
</ul>

<h3><a name='CmdGetChildren'>Get Children</a></h3>

<pre><b><font face="Courier New" size=2 color=#333399>
C &bull; <i>&lt;token&gt;</i> &bull; Registers &bull; getChildren &bull; <i>&lt;string: parent context ID&gt;</i> &bull;
</font></b></pre>

<p>The command requests a list of contexts available for registers access commands.</p>

<p>Parent context ID is usually a thread ID retrieved through Run Control Service or one
of context IDs retrieved by previous getChildren commands.
Contexts hierarchy can be simple plain list of registers, or it can form a tree of register groups, registers and bit fields.
It is up to target agent developers to choose layout that is most descriptive for a given target.</p>

<p>Reply:</p>

<pre><b><font face="Courier New" size=2 color=#333399>
R &bull; <i>&lt;token&gt;</i> &bull; <i>&lt;error report&gt;</i> &bull; <i>&lt;array of context IDs&gt;</i> &bull;<i></i>

<i>&lt;array of context IDs&gt;</i>
    &rArr; null
    &rArr; [ ]
    &rArr; [ <i>&lt;context ID list&gt;</i> ]

<i>&lt;context ID list&gt;</i>
    &rArr; <i>&lt;string: context ID&gt;</i>
    &rArr; <i>&lt;context ID list&gt;</i> , <i>&lt;string: context ID&gt;</i>

</font></b></pre>

<h3><a name='CmdSetRegister'>Set Register</a></h3>

<pre><b><font face="Courier New" size=2 color=#333399>
C &bull; &lt;token&gt; &bull; Registers &bull; set &bull; <i>&lt;string: context ID&gt;</i> &bull; <i>&lt;string: value&gt;</i> &bull;
</font></b></pre>

<p>Writes value into given register context. Context ID must be one returned by getContexts.
Value is BASE64 encoded byte array of binary data. Array size should match the size of the register.</p>

<p>Result message:</p>

<pre><b><font face="Courier New" size=2 color=#333399>
R &bull; <i>&lt;token&gt;</i> &bull; <i>&lt;error report&gt;</i> &bull;
</font></b></pre>

<p>Error report provides integer error code and a short, human readable explanation
of error.</p>

<h3><a name='CmdGetRegister'>Get Register</a></h3>

<pre><b><font face="Courier New" size=2 color=#333399>
C &bull; &lt;token&gt; &bull; Registers &bull; get &bull; <i>&lt;string: context ID&gt;</i> &bull;
</font></b></pre>

<p>Reads register value from given register context. Context ID must be one returned by getContexts.
</p>

<p>Result message:</p>

<pre><b><font face="Courier New" size=2 color=#333399>
R &bull; <i>&lt;token&gt;</i> &bull; <i>&lt;error report&gt;</i> &bull; <i>&lt;string: value&gt;</i> &bull;
</font></b></pre>

<p>Error report provides integer error code and a short, human readable explanation
of error. Value is BASE64 encoded byte array of binary data. Array size should match the size of the register.</p>

<h3><a name='CmdSetMultiple'>Set Multiple Registers</a></h3>

<pre><b><font face="Courier New" size=2 color=#333399>
C &bull; &lt;token&gt; &bull; Registers &bull; setm &bull; <i>&lt;array of locations&gt;</i> &bull; <i>&lt;string: value&gt;</i> &bull;

<i>&lt;array of locations&gt;</i>
    &rArr; [ <i>&lt;location list&gt;</i> ]

<i>&lt;location list&gt;</i>
    &rArr; <i>&lt;location&gt;</i>
    &rArr; <i>&lt;location list&gt;</i> , <i>&lt;location&gt;</i>

<i>&lt;location&gt;</i>
    &rArr; [ <i>&lt;string: register context ID&gt;</i> , <i>&lt;int: offset in bytes&gt;</i> , <i>&lt;int: size in bytes&gt;</i> ]
</font></b></pre>

<p>Writes value into given list of locations in registers. Each location is represented by 3-element array that consists of
context ID, offset in the context in bytes and value size in bytes.
Value is BASE64 encoded byte array of binary data. Byte array size should match the sum of location sizes.</p>

<p>Result message:</p>

<pre><b><font face="Courier New" size=2 color=#333399>
R &bull; <i>&lt;token&gt;</i> &bull; <i>&lt;error report&gt;</i> &bull;
</font></b></pre>

<p>Error report provides integer error code and a short, human readable explanation
of error.</p>

<h3><a name='CmdGetMultiple'>Get Multiple Registers</a></h3>

<pre><b><font face="Courier New" size=2 color=#333399>
C &bull; &lt;token&gt; &bull; Registers &bull; getm &bull; <i>&lt;array of locations&gt;</i> &bull;

<i>&lt;array of locations&gt;</i>
    &rArr; [ <i>&lt;location list&gt;</i> ]

<i>&lt;location list&gt;</i>
    &rArr; <i>&lt;location&gt;</i>
    &rArr; <i>&lt;location list&gt;</i> , <i>&lt;location&gt;</i>

<i>&lt;location&gt;</i>
    &rArr; [ <i>&lt;string: register context ID&gt;</i> , <i>&lt;int: offset in bytes&gt;</i> , <i>&lt;int: size in bytes&gt;</i> ]
</font></b></pre>

<p>Reads register values from given list of locations in registers. Each location is represented by 3-element array that consists of
context ID, offset in the context in bytes and value size in bytes.
</p>

<p>Result message:</p>

<pre><b><font face="Courier New" size=2 color=#333399>
R &bull; <i>&lt;token&gt;</i> &bull; <i>&lt;error report&gt;</i> &bull; <i>&lt;string: value&gt;</i> &bull;
</font></b></pre>

<p>Error report provides integer error code and a short, human readable explanation
of error. Value is BASE64 encoded byte array of binary data. Byte array size should match the sum of location sizes.</p>

<h3><a name='CmdSearch'>Search for Registers</a></h3>

<pre><b><font face="Courier New" size="2" color="#333399">
C &bull; &lt;token&gt; &bull; Registers &bull; search &bull; <i>&lt;string: start context ID&gt; &bull; &lt;object:filter properties&gt;</i> &bull;
</font></b></pre>

<p>Search returns a path to each context with properties matching the filter. A path consists of a list of
    context ids starting with a direct child of the start context up to the found context.
    Search is only supported for properties listed in the CanSearch property.

<p>Predefined filter object properties are:</p>
<ul>
    <li><code><b><font face="Courier New" size="2" color="#333399">"Name" : <i>&lt;string&gt;</i></font></b></code>
    - The name of the property this filter applies to. Must be one of the names listed in the CanSearch property.
        </li>
    <li><code><b><font face="Courier New" size="2" color="#333399">"EqualValue" : <i>&lt;string&gt;</i></font></b></code>
    - The value which is searched for.
        </li>
</ul>
</p>

<p>Result message:</p>

<pre><b><font face="Courier New" size="2" color="#333399">
R &bull; <i>&lt;token&gt;</i> &bull; <i>&lt;error report&gt;</i> &bull; <i>&lt;array of context Paths&gt;</i> &bull;

<i>&lt;array of context Paths&gt;</i>
    &rArr; null
    &rArr; [ ]
    &rArr; [ <i>&lt;context Path list&gt;</i> ]

<i>&lt;context Path list&gt;</i>
    &rArr; <i>&lt;array of context IDs&gt;</i>
    &rArr; <i>&lt;context Path list&gt;</i> , <i>&lt;array of context IDs&gt;</i>

</font></b></pre>

<p>Error report provides integer error code and a short, human readable explanation of error.
In the result, each matching context is provided with the path of parents starting with the direct
children of the starting node up to the matching node.
Multiple found entries are returned as an array of those paths.
</p>
Example Assume the following context hierarchy:

<pre><b><font face="Courier New" size="2">
{"Name" : "Core", "ID":"ID_C"}
        {"Name" : "Group0", "ID":"ID_G0", "Role":"CORE"}
                {"Name" : "PC", "ID":"ID_PC", "Role":"PC"}
                {"Name" : "SP", "ID":"ID_SP", "Role":"SP"}
        {"Name" : "Group1", "ID":"ID_G1"}
                {"Name" : "R0", "ID":"ID_R0"}
</font></b></pre>

With this setup, the following commands and responses could take place:

<pre><b><font face="Courier New" size="2">
C &bull; "1234" &bull; Registers &bull; search &bull; "ID_C" &bull; {"Name":"Name", "EqualValue":"PC"} &bull;
R &bull; "1234" &bull; [["ID_G0", "ID_PC"]] &bull;

C &bull; "1235" &bull; Registers &bull; search &bull; "ID_C" &bull; {"Name":"Role", "EqualValue":"CORE"} &bull;
R &bull; "1235" &bull; [["ID_G0"]] &bull;
</font></b></pre>

<h2><a name='Events'>Events</a></h2>

<p>Registers service broadcasts notification events when registers contexts are changed, and when
a register content is altered by "set" commands.</p>

<pre><b><font face="Courier New" size="2" color="#333399">
E &bull; Registers &bull; contextChanged &bull;
E &bull; Registers &bull; registerChanged &bull; <i>&lt;string: context ID&gt;</i> &bull;
</font></b></pre>

<h2><a name='API'>API</a></h2>

<pre>
<font color=#3F5FBF>/**
 * IRegisters service provides access to target CPU register values and properties.
 */</font>
<font color=#7F0055>public interface</font> IRegisters <font color=#7F0055>extends</font> IService {

    <font color=#7F0055>static final</font> String NAME = "Registers";

    <font color=#3F5FBF>/**
     * Context property names.
     */</font>
    <font color=#7F0055>static final</font> String
        PROP_ID = "ID",                         <font color=#3F5FBF>/** String, ID of the context */</font>
        PROP_PARENT_ID = "ParentID",            <font color=#3F5FBF>/** String, ID of a parent context */</font>
        PROP_PROCESS_ID = "ProcessID",          <font color=#3F5FBF>/** String, process ID */</font>
        PROP_NAME = "Name",                     <font color=#3F5FBF>/** String, context name */</font>
        PROP_DESCRIPTION = "Description",       <font color=#3F5FBF>/** String, context description */</font>
        PROP_SIZE = "Size",                     <font color=#3F5FBF>/** Number, context size in bytes. Byte arrays in get/set commands should be same size */</font>
        PROP_READBLE = "Readable",              <font color=#3F5FBF>/** Boolean, true if context value can be read */</font>
        PROP_READ_ONCE = "ReadOnce",            <font color=#3F5FBF>/** Boolean, true if reading the context (register) destroys its current value */</font>
        PROP_WRITEABLE = "Writeable",           <font color=#3F5FBF>/** Boolean, true if context value can be written */</font>
        PROP_WRITE_ONCE = "WriteOnce",          <font color=#3F5FBF>/** Boolean, true if register value can not be overwritten - every write counts */</font>
        PROP_SIDE_EFFECTS = "SideEffects",      <font color=#3F5FBF>/** Boolean, true if writing the context can change values of other registers */</font>
        PROP_VOLATILE = "Volatile",             <font color=#3F5FBF>/** Boolean, true if the register value can change even when target is stopped */</font>
        PROP_FLOAT = "Float",                   <font color=#3F5FBF>/** Boolean, true if the register value is a floating-point value */</font>
        PROP_BIG_ENDIAN = "BigEndian",          <font color=#3F5FBF>/** Boolean, true if big endian */</font>
        PROP_LEFT_TO_RIGHT = "LeftToRight",     <font color=#3F5FBF>/** Boolean, true if the lowest numbered bit should be shown to user as the left-most bit */</font>
        PROP_FIST_BIT = "FirstBit",             <font color=#3F5FBF>/** Number, bit numbering base (0 or 1) to use when showing bits to user */</font>
        PROP_BITS = "Bits",                     <font color=#3F5FBF>/** Number, if context is a bit field, contains the field bit numbers in the parent context */</font>
        PROP_VALUES = "Values",                 <font color=#3F5FBF>/** Array of Map, predefined names (mnemonics) for some of context values */</font>
        PROP_MEMORY_ADDRESS = "MemoryAddress",  <font color=#3F5FBF>/** Number, the address of a memory mapped register */</font>
        PROP_MEMORY_CONTEXT = "MemoryContext",  <font color=#3F5FBF>/** String, the context ID of a memory context in which a memory mapped register is located */</font>
        PROP_CAN_SEARCH = "CanSearch",          <font color=#3F5FBF>/** Array of String, a list of attribute names which can be searched for starting on this context */</font>
        PROP_ROLE = "Role";                     <font color=#3F5FBF>/** String, the role the register plays in a program execution */</font>

    <font color=#3F5FBF>/**
     * Role property names.
     */</font>
    <font color=#7F0055>static final</font> String
        ROLE_PC = "PC",                         <font color=#3F5FBF>/** Program counter. Defines instruction to execute next */</font>
        ROLE_SP = "SP",                         <font color=#3F5FBF>/** Register defining the current stack pointer location */</font>
        ROLE_FP = "FP",                         <font color=#3F5FBF>/** Register defining the current frame pointer location */</font>
        ROLE_RET = "RET",                       <font color=#3F5FBF>/** Register used to store the return address for calls */</font>
        ROLE_CORE = "CORE";                     <font color=#3F5FBF>/** Indicates register or register groups which belong to the core state */</font>

    <font color=#3F5FBF>/**
     * Filter property names.
     */</font>
    <font color=#7F0055>static final</font> String
        SEARCH_NAME = "Name",                   <font color=#3F5FBF>/** The name of the property this filter applies too */</font>
        SEARCH_EQUAL_VALUE = "EqualValue";      <font color=#3F5FBF>/** The value which is searched for */</font>


    <font color=#3F5FBF>/**
     * Retrieve context info for given context ID.
     *
     * <font color=#7F9FBF>@param</font> id &ndash; context ID.
     * <font color=#7F9FBF>@param</font> done - call back interface called when operation is completed.
     */</font>
    IToken getContext(String id, DoneGetContext done);

    <font color=#3F5FBF>/**
     * Client call back interface for getContext().
     */</font>
    <font color=#7F0055>interface</font> DoneGetContext {
        <font color=#3F5FBF>/**
         * Called when contexts data retrieval is done.
         * <font color=#7F9FBF>@param</font> error &ndash; error description if operation failed, null if succeeded.
         * <font color=#7F9FBF>@param</font> context &ndash; context data.
         */</font>
        <font color=#7F0055>void</font> doneGetContext(IToken token, Exception error, RegistersContext context);
    }

    <font color=#3F5FBF>/**
     * Retrieve contexts available for registers commands.
     * A context corresponds to an execution thread, stack frame, registers group, etc.
     * A context can belong to a parent context. Contexts hierarchy can be simple
     * plain list or it can form a tree. It is up to target agent developers to choose
     * layout that is most descriptive for a given target. Context IDs are valid across
     * all services. In other words, all services access same hierarchy of contexts,
     * with same IDs, however, each service accesses its own subset of context's
     * attributes and functionality, which is relevant to that service.
     *
     * <font color=#7F9FBF>@param</font> parent_context_id &ndash; parent context ID. Can be null &ndash;
     * to retrieve top level of the hierarchy, or one of context IDs retrieved
     * by previous getChildren commands.
     * <font color=#7F9FBF>@param</font> done - call back interface called when operation is completed.
     */</font>
    IToken getChildren(String parent_context_id, DoneGetChildren done);

    <font color=#3F5FBF>/**
     * Client call back interface for getChildren().
     */</font>
    <font color=#7F0055>interface</font> DoneGetChildren {
        <font color=#3F5FBF>/**
         * Called when contexts data retrieval is done.
         * <font color=#7F9FBF>@param</font> error &ndash; error description if operation failed, null if succeeded.
         * <font color=#7F9FBF>@param</font> context_ids &ndash; array of available context IDs.
         */</font>
        <font color=#7F0055>void</font> doneGetChildren(IToken token, Exception error, String[] context_ids);
    }

    <font color=#3F5FBF>/**
     * RegistersContext objects represent register groups, registers and bit fields.
     */</font>
    <font color=#7F0055>interface</font> RegistersContext {
        <font color=#3F5FBF>/**
         * Get Context ID.
         * <font color=#7F9FBF>@return</font> context ID.
         */</font>
        String getID();

        <font color=#3F5FBF>/**
         * Get parent context ID.
         * <font color=#7F9FBF>@return</font> parent context ID.
         */</font>
        String getParentID();

        <font color=#3F5FBF>/**
         * Get context (register, register group, bit field) name.
         * <font color=#7F9FBF>@return</font> context name.
         */</font>
        String getName();

        <font color=#3F5FBF>/**
         * Get context description.
         * <font color=#7F9FBF>@return</font> context description.
         */</font>
        String getDescription();

        <font color=#3F5FBF>/**
         * Get context size in bytes.
         * Byte arrays in get()/set() methods should be same size.
         * Hardware register can be smaller then this size, for example in case
         * when register size is not an even number of bytes. In such case implementation
         * should add/remove padding that consists of necessary number of zero bits.
         * @return context size in bytes.
         */</font>
        <font color=#7F0055>int</font> getSize();

        <font color=#3F5FBF>/**
         * Check if context value can be read.
         * <font color=#7F9FBF>@return</font> true if can read value of the context.
         */</font>
        <font color=#7F0055>boolean</font> isReadable();

        <font color=#3F5FBF>/**
         * Check if reading the context (register) destroys its current value -
         * it can be read only once.
         * <font color=#7F9FBF>@return</font> true if read-once register.
         */</font>
        <font color=#7F0055>boolean</font> isReadOnce();

        <font color=#3F5FBF>/**
         * Check if context value can be written.
         * <font color=#7F9FBF>@return</font> true if can write value of the context.
         */</font>
        <font color=#7F0055>boolean</font> isWriteable();

        <font color=#3F5FBF>/**
         * Check if register value can not be overwritten - every write counts.
         * <font color=#7F9FBF>@return</font> true if write-once register.
         */</font>
        <font color=#7F0055>boolean</font> isWriteOnce();

        <font color=#3F5FBF>/**
         * Check if writing the context can change values of other registers.
         * <font color=#7F9FBF>@return</font> true if has side effects.
         */</font>
        <font color=#7F0055>boolean</font> hasSideEffects();

        <font color=#3F5FBF>/**
         * Check if the register value can change even when target is stopped.
         * <font color=#7F9FBF>@return</font> true if the register value can change at any time.
         */</font>
        <font color=#7F0055>boolean</font> isVolatile();

        <font color=#3F5FBF>/**
         * Check if the register value is a floating-point value.
         * <font color=#7F9FBF>@return</font> true if a floating-point register.
         */</font>
        <font color=#7F0055>boolean</font> isFloat();

        <font color=#3F5FBF>/**
         * Check endianess of the context.
         * Big endian means decreasing numeric significance with increasing bit number.
         * <font color=#7F9FBF>@return</font> true if big endian.
         */</font>
        <font color=#7F0055>boolean</font> isBigEndian();

        <font color=#3F5FBF>/**
         * Check if the lowest numbered bit (i.e. bit #0 or bit #1 depending on
         * getFirstBitNumber() value) should be shown to user as the left-most bit or
         * the right-most bit.
         * <font color=#7F9FBF>@return</font> true if the first bit is left-most bit.
         */</font>
        <font color=#7F0055>boolean</font> isLeftToRight();

        <font color=#3F5FBF>/**
         * If the context has bit field children, bit positions of the fields
         * can be zero-based or 1-based.
         * <font color=#7F9FBF>@return</font> first bit position - 0 or 1.
         */</font>
        <font color=#7F0055>int</font> getFirstBitNumber();

        <font color=#3F5FBF>/**
         * If context is a bit field, get the field bit numbers in parent context.
         * <font color=#7F9FBF>@return</font> array of bit numbers.
         */</font>
        <font color=#7F0055>int</font>[] getBitNumbers();

        <font color=#3F5FBF>/**
         * A context can have predefined names (mnemonics) for some its values.
         * This method returns a list of such named values.
         * <font color=#7F9FBF>@return</font> array of named values or null.
         */</font>
        NamedValue[] getNamedValues();

        <font color=#3F5FBF>/**
         * Get the address of a memory mapped register.
         * <font color=#7F9FBF>@return</font> address.
         */</font>
        Number getMemoryAddress();

        <font color=#3F5FBF>/**
         * Get the context ID of a memory context in which a memory mapped register is located.
         * <font color=#7F9FBF>@return</font> memory context ID.
         */</font>
        String getMemoryContext();

        <font color=#3F5FBF>/**
         * Get a list of property names which can be searched for starting on this context
         * <font color=#7F9FBF>@return</font> collection of property names.
         */</font>
        Collection<String> canSearch();

        <font color=#3F5FBF>/**
         * Get the role the register plays in a program execution.
         * <font color=#7F9FBF>@return</font> role name.
         */</font>
        String getRole();

        <font color=#3F5FBF>/**
         * Get complete map of context properties.
         * <font color=#7F9FBF>@return</font> map of all available context properties.
         */</font>
        Map<String,Object> getProperties();

        <font color=#3F5FBF>/**
         * Read value of the context.
         * <font color=#7F9FBF>@param</font> done - call back object.
         * <font color=#7F9FBF>@return</font> - pending command handle.
         */</font>
        IToken get(DoneGet done);

        <font color=#3F5FBF>/**
         * Set value of the context.
         * <font color=#7F9FBF>@param</font> value - value to write into the context.
         * <font color=#7F9FBF>@param</font> done - call back object.
         * <font color=#7F9FBF>@return</font> - pending command handle.
         */</font>
        IToken set(byte[] value, DoneSet done);

       <font color=#3F5FBF>/**
         * Search register contexts that passes given search filter.
         * Search is only supported for properties listed in the "CanSearch" property.
         * <font color=#7F9FBF>@param</font> filter - properties bag that defines search filter.
         * <font color=#7F9FBF>@param</font> done - call back object.
         * <font color=#7F9FBF>@return</font> - pending command handle.
         */</font>
         IToken search(Map&lt;String,Object&gt; filter, DoneSearch done);
    }

    <font color=#3F5FBF>/**
     * A register context can have predefined names (mnemonics) for some its values.
     * NamedValue objects represent such values.
     */</font>
    <font color=#7F0055>interface</font> NamedValue {
        <font color=#3F5FBF>/**
         * Get value associated with the name.
         * <font color=#7F9FBF>@return</font> the value as an array of bytes.
         */</font>
        byte[] getValue();

        <font color=#3F5FBF>/**
         * Get name (mnemonic) of the value.
         * <font color=#7F9FBF>@return</font> value name.
         */</font>
        String getName();

        <font color=#3F5FBF>/**
         * Get human readable description of the value.
         * <font color=#7F9FBF>@return</font> value description.
         */</font>
        String getDescription();
    }

    <font color=#3F5FBF>/**
     * Read values of multiple locations in registers.
     * <font color=#7F9FBF>@param</font> locs - array of data locations.
     * <font color=#7F9FBF>@param</font> done - call back object.
     * <font color=#7F9FBF>@return</font> - pending command handle.
     */</font>
    IToken getm(Location[] locs, DoneGet done);

    <font color=#3F5FBF>/**
     * Set values of multiple locations in registers.
     * <font color=#7F9FBF>@param</font> locs - array of data locations.
     * <font color=#7F9FBF>@param</font> value - value to write into the context.
     * <font color=#7F9FBF>@param</font> done - call back object.
     * <font color=#7F9FBF>@return</font> - pending command handle.
     */</font>
    IToken setm(Location[] locs, byte[] value, DoneSet done);

    <font color=#3F5FBF>/**
     * Class Location represents value location in register context
     */</font>
    <font color=#7F0055>final class</font> Location {
        <font color=#3F5FBF>/** Register context ID */</font>
        <font color=#7F0055>public final</font> String id;

        <font color=#3F5FBF>/** offset in the context, in bytes */</font>
        <font color=#7F0055>public final int</font> offs;

        <font color=#3F5FBF>/** value size in bytes */</font>
        <font color=#7F0055>public final int</font> size;

        <font color=#7F0055>public</font> Location(String id, <font color=#7F0055>int</font> offs, <font color=#7F0055>int</font> size) {
            <font color=#7F0055>this</font>.id = id;
            <font color=#7F0055>this</font>.offs = offs;
            <font color=#7F0055>this</font>.size = size;
        }
    }

    <font color=#3F5FBF>/**
     * 'get' command call back interface.
     */</font>
    <font color=#7F0055>interface</font> DoneGet {
        <font color=#3F5FBF>/**
         * Called when value retrieval is done.
         * <font color=#7F9FBF>@param</font> token - command handle
         * <font color=#7F9FBF>@param</font> error - error description if operation failed, null if succeeded.
         * <font color=#7F9FBF>@param</font> value - context value as array of bytes.
         */</font>
        <font color=#7F0055>void</font> doneGet(IToken token, Exception error, byte[] value);
    }

    <font color=#3F5FBF>/**
     * 'set' command call back interface.
     */</font>
    <font color=#7F0055>interface</font> DoneSet {
        <font color=#3F5FBF>/**
         * Called when value setting is done.
         * <font color=#7F9FBF>@param</font> token - command handle.
         * <font color=#7F9FBF>@param</font> error - error description if operation failed, null if succeeded.
         */</font>
        <font color=#7F0055>void</font> doneSet(IToken token, Exception error);
    }

    <font color=#3F5FBF>/**
     * 'search' command call back interface.
     */</font>
    <font color=#7F0055>interface</font> DoneSearch {
        <font color=#3F5FBF>/**
         * Called when context search is done.
         * <font color=#7F9FBF>@param</font> token - command handle.
         * <font color=#7F9FBF>@param</font> error - error description if operation failed, null if succeeded.
         * <font color=#7F9FBF>@param</font> paths - array of paths to each context with properties matching the filter
         */</font>
        <font color=#7F0055>void</font> doneSearch(IToken token, String[][] paths);
    }

    <font color=#3F5FBF>/**
     * Add registers service event listener.
     * <font color=#7F9FBF>@param</font> listener - event listener implementation.
     */</font>
    <font color=#7F0055>void</font> addListener(RegistersListener listener);

    <font color=#3F5FBF>/**
     * Remove registers service event listener.
     * <font color=#7F9FBF>@param</font> listener - event listener implementation.
     */</font>
    <font color=#7F0055>void</font> removeListener(RegistersListener listener);

    <font color=#3F5FBF>/**
     * Registers event listener is notified when registers context hierarchy
     * changes, and when a register is modified by the service commands.
     */</font>
    <font color=#7F0055>interface</font> RegistersListener {

        <font color=#3F5FBF>/**
         * Called when register context properties changed.
         * Most targets have static set of registers and register properties.
         * Such targets never generate this event. However, some targets,
         * for example, JTAG probes, allow user to modify register definitions.
         * Clients should flush all cached register context data.
         */</font>
        <font color=#7F0055>void</font> contextChanged();

        <font color=#3F5FBF>/**
         * Called when register content was changed and clients
         * need to update themselves. Clients, at least, should invalidate
         * corresponding cached registers data.
         * Not every change is notified - it is not possible,
         * only those, which are not caused by normal execution of the debuggee.
         * At least, changes caused by "set" command should be notified.
         * <font color=#7F9FBF>@param</font> id - register context ID.
         */</font>
        <font color=#7F0055>void</font> registerChanged(String context_id);
    }
}
</pre>

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