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<html>
<head>
<title>openMSP430 Serial Debug Interface</title>
</head>
<body>
<a name="TOC"></a>
<h3>Table of content</h3>
<ul>
<li><a href="#1. Introduction"> 1. Introduction</a></li>
<li><a href="#2. Debug Unit"> 2. Debug Unit</a>
<ul>
<li><a href="#2.1 Register Mapping"> 2.1 Register Mapping</a></li>
<li><a href="#2.2 CPU Control/Status Registers"> 2.2 CPU Control/Status Registers</a></li>
<ul>
<li><a href="#2.2.1 CPU_ID"> 2.2.1 CPU_ID</a></li>
<li><a href="#2.2.2 CPU_CTL"> 2.2.2 CPU_CTL</a></li>
<li><a href="#2.2.3 CPU_STAT"> 2.2.3 CPU_STAT</a></li>
</ul>
<li><a href="#2.3 Memory Access Registers"> 2.3 Memory Access Registers</a></li>
<ul>
<li><a href="#2.3.1 MEM_CTL"> 2.3.1 MEM_CTL</a></li>
<li><a href="#2.3.2 MEM_ADDR"> 2.3.2 MEM_ADDR</a></li>
<li><a href="#2.3.3 MEM_DATA"> 2.3.3 MEM_DATA</a></li>
<li><a href="#2.3.4 MEM_CNT"> 2.3.4 MEM_CNT</a></li>
</ul>
<li><a href="#2.4 Hardware Breakpoint Unit Registers">2.4 Hardware Breakpoint Unit Registers</a></li>
<ul>
<li><a href="#2.4.1 BRKx_CTL"> 2.4.1 BRKx_CTL</a></li>
<li><a href="#2.4.2 BRKx_STAT"> 2.4.2 BRKx_STAT</a></li>
<li><a href="#2.4.3 BRKx_ADDR0"> 2.4.3 BRKx_ADDR0</a></li>
<li><a href="#2.4.4 BRKx_ADDR1"> 2.4.4 BRKx_ADDR1</a></li>
</ul>
</ul>
</li>
<li><a href="#3. Debug Communication Interface: UART"> 3. Debug Communication Interface: UART</a>
<ul>
<li><a href="#3.1 Serial communication protocol: 8N1"> 3.1 Serial communication protocol: 8N1</a></li>
<li><a href="#3.2 Synchronization frame"> 3.2 Synchronization frame</a></li>
<li><a href="#3.3 Read/Write access to the debug registers"> 3.3 Read/Write access to the debug registers</a></li>
<ul>
<li><a href="#3.3.1 Command Frame"> 3.3.1 Command Frame</a></li>
<li><a href="#3.3.2 Write access"> 3.3.2 Write access</a></li>
<li><a href="#3.3.3 Read access"> 3.3.3 Read access</a></li>
</ul>
<li><a href="#3.4 Read/Write burst implementation for the CPU Memory access">3.4 Read/Write burst implementation for the CPU Memory access</a></li>
<ul>
<li><a href="#3.4.1 Write Burst access"> 3.4.1 Write Burst access</a></li>
<li><a href="#3.4.2 Read Burst access"> 3.4.2 Read Burst access</a></li>
</ul>
</ul>
</ul>
<a name="1. Introduction"></a>
<h1>1. Introduction</h1>
The original MSP430 from TI provides a serial debug interface to give a simple path to software development. In that case, the communication with the host computer is typically build on a JTAG or Spy-Bi-Wire serial protocol. However, the global debug architecture from the MSP430 is unfortunately poorly documented on the web (and is also probably tightly linked with the internal core architecture).
<br /><br />
A custom module has therefore been implemented for the openMSP430. The communication with the host is done with a simple RS232 cable (8N1 serial protocol) and the debug unit provides all the required features for Nexus Class 3 debugging (beside trace), namely:
<ul>
<li>CPU control (run, stop, step, reset).</li>
<li>Software & hardware breakpoint support.</li>
<li>Memory read/write on-the-fly (no need to halt execution).</li>
<li>CPU registers read/write on-the-fly (no need to halt execution).</li>
</ul>
<a name="2. Debug Unit"></a>
<div style="text-align: right"><a href="#TOC">Top</a></div>
<h1>2. Debug Unit</h1>
<a name="2.1 Register Mapping"></a>
<h2>2.1 Register Mapping</h2>
The following table summarize the complete debug register set accessible through the debug communication interface:
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1">15</font></td><td><font size="-1">14</font></td>
<td><font size="-1">13</font></td><td><font size="-1">12</font></td>
<td><font size="-1">11</font></td><td><font size="-1">10</font></td>
<td><font size="-1"> 9</font></td><td><font size="-1"> 8</font></td>
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.2.1 CPU_ID">CPU_ID_LO</a></font></td>
<td><font size="-1">0x00</font></td>
<td colspan="7"><font size="-5">PER_SPACE</font></td>
<td colspan="5"><font size="-5">USER_VERSION</font></td>
<td colspan="1"><font size="-5">ASIC</font></td>
<td colspan="3"><font size="-5">CPU_VERSION</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.2.1 CPU_ID">CPU_ID_HI</a></font></td>
<td><font size="-1">0x01</font></td>
<td colspan="6"><font size="-5">PMEM_SIZE</font></td>
<td colspan="9"><font size="-5">DMEM_SIZE</font></td>
<td colspan="1"><font size="-5">MPY</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.2.2 CPU_CTL">CPU_CTL</a></font></td>
<td><font size="-1">0x02</font></td>
<td colspan="9"><font size="-5">Reserved</font></td>
<td><font size="-5">CPU_RST</font></td>
<td><font size="-5">RST_BRK_EN</font></td>
<td><font size="-5">FRZ_BRK_EN</font></td>
<td><font size="-5">SW_BRK_EN</font></td>
<td><font size="-5">ISTEP</font></td>
<td><font size="-5">RUN</font></td>
<td><font size="-5">HALT</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.2.3 CPU_STAT">CPU_STAT</a></font></td>
<td><font size="-1">0x03</font></td>
<td colspan="8"><font size="-5">Reserved</font></td>
<td><font size="-5">HWBRK3_PND</font></td>
<td><font size="-5">HWBRK2_PND</font></td>
<td><font size="-5">HWBRK1_PND</font></td>
<td><font size="-5">HWBRK0_PND</font></td>
<td><font size="-5">SWBRK_PND</font></td>
<td><font size="-5">PUC_PND</font></td>
<td><font size="-5">Res.</font></td>
<td><font size="-5">HALT_RUN</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.3.1 MEM_CTL">MEM_CTL</a></font></td>
<td><font size="-1">0x04</font></td>
<td colspan="12"><font size="-5">Reserved</font></td>
<td><font size="-5">B/W</font></td>
<td><font size="-5">MEM/REG</font></td>
<td><font size="-5">RD/WR</font></td>
<td><font size="-5">START</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.3.2 MEM_ADDR">MEM_ADDR</a></font></td>
<td><font size="-1">0x05</font></td>
<td colspan="16"><font size="-5">MEM_ADDR[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.3.3 MEM_DATA">MEM_DATA</a></font></td>
<td><font size="-1">0x06</font></td>
<td colspan="16"><font size="-5">MEM_DATA[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.3.4 MEM_CNT">MEM_CNT</a></font></td>
<td><font size="-1">0x07</font></td>
<td colspan="16"><font size="-5">MEM_CNT[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.1 BRKx_CTL">BRK0_CTL</a></font></td>
<td><font size="-1">0x08</font></td>
<td colspan="11"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_MODE</font></td>
<td><font size="-5">INST_EN</font></td>
<td><font size="-5">BREAK_EN</font></td>
<td colspan="2"><font size="-5">ACCESS_MODE</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.2 BRKx_STAT">BRK0_STAT</a></font></td>
<td><font size="-1">0x09</font></td>
<td colspan="10"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_WR</font></td>
<td><font size="-5">RANGE_RD</font></td>
<td><font size="-5">ADDR1_WR</font></td>
<td><font size="-5">ADDR1_RD</font></td>
<td><font size="-5">ADDR0_WR</font></td>
<td><font size="-5">ADDR0_RD</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.3 BRKx_ADDR0">BRK0_ADDR0</a></font></td>
<td><font size="-1">0x0A</font></td>
<td colspan="16"><font size="-5">BRK_ADDR0[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.4 BRKx_ADDR1">BRK0_ADDR1</a></font></td>
<td><font size="-1">0x0B</font></td>
<td colspan="16"><font size="-5">BRK_ADDR1[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.1 BRKx_CTL">BRK1_CTL</a></font></td>
<td><font size="-1">0x0C</font></td>
<td colspan="11"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_MODE</font></td>
<td><font size="-5">INST_EN</font></td>
<td><font size="-5">BREAK_EN</font></td>
<td colspan="2"><font size="-5">ACCESS_MODE</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.2 BRKx_STAT">BRK1_STAT</a></font></td>
<td><font size="-1">0x0D</font></td>
<td colspan="10"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_WR</font></td>
<td><font size="-5">RANGE_RD</font></td>
<td><font size="-5">ADDR1_WR</font></td>
<td><font size="-5">ADDR1_RD</font></td>
<td><font size="-5">ADDR0_WR</font></td>
<td><font size="-5">ADDR0_RD</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.3 BRKx_ADDR0">BRK1_ADDR0</a></font></td>
<td><font size="-1">0x0E</font></td>
<td colspan="16"><font size="-5">BRK_ADDR0[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.4 BRKx_ADDR1">BRK1_ADDR1</a></font></td>
<td><font size="-1">0x0F</font></td>
<td colspan="16"><font size="-5">BRK_ADDR1[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.1 BRKx_CTL">BRK2_CTL</a></font></td>
<td><font size="-1">0x10</font></td>
<td colspan="11"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_MODE</font></td>
<td><font size="-5">INST_EN</font></td>
<td><font size="-5">BREAK_EN</font></td>
<td colspan="2"><font size="-5">ACCESS_MODE</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.2 BRKx_STAT">BRK2_STAT</a></font></td>
<td><font size="-1">0x11</font></td>
<td colspan="10"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_WR</font></td>
<td><font size="-5">RANGE_RD</font></td>
<td><font size="-5">ADDR1_WR</font></td>
<td><font size="-5">ADDR1_RD</font></td>
<td><font size="-5">ADDR0_WR</font></td>
<td><font size="-5">ADDR0_RD</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.3 BRKx_ADDR0">BRK2_ADDR0</a></font></td>
<td><font size="-1">0x12</font></td>
<td colspan="16"><font size="-5">BRK_ADDR0[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.4 BRKx_ADDR1">BRK2_ADDR1</a></font></td>
<td><font size="-1">0x13</font></td>
<td colspan="16"><font size="-5">BRK_ADDR1[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.1 BRKx_CTL">BRK3_CTL</a></font></td>
<td><font size="-1">0x14</font></td>
<td colspan="11"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_MODE</font></td>
<td><font size="-5">INST_EN</font></td>
<td><font size="-5">BREAK_EN</font></td>
<td colspan="2"><font size="-5">ACCESS_MODE</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.2 BRKx_STAT">BRK3_STAT</a></font></td>
<td><font size="-1">0x15</font></td>
<td colspan="10"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_WR</font></td>
<td><font size="-5">RANGE_RD</font></td>
<td><font size="-5">ADDR1_WR</font></td>
<td><font size="-5">ADDR1_RD</font></td>
<td><font size="-5">ADDR0_WR</font></td>
<td><font size="-5">ADDR0_RD</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.3 BRKx_ADDR0">BRK3_ADDR0</a></font></td>
<td><font size="-1">0x16</font></td>
<td colspan="16"><font size="-5">BRK_ADDR0[15:0]</font></td>
</tr>
<tr align="center">
<td><font size="-1"><a href="#2.4.4 BRKx_ADDR1">BRK3_ADDR1</a></font></td>
<td><font size="-1">0x17</font></td>
<td colspan="16"><font size="-5">BRK_ADDR1[15:0]</font></td>
</tr>
</table>
<a name="2.2 CPU Control/Status Registers"></a>
<div style="text-align: right"><a href="#TOC">Top</a></div>
<h2>2.2 CPU Control/Status Registers</h2>
<a name="2.2.1 CPU_ID"></a>
<h3>2.2.1 CPU_ID</h3>
This 32 bit read-only register holds the program and data memory size information of the implemented openMSP430.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1">15</font></td><td><font size="-1">14</font></td>
<td><font size="-1">13</font></td><td><font size="-1">12</font></td>
<td><font size="-1">11</font></td><td><font size="-1">10</font></td>
<td><font size="-1"> 9</font></td><td><font size="-1"> 8</font></td>
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">CPU_ID_LO</font></td>
<td><font size="-1">0x00</font></td>
<td colspan="7"><font size="-5">PER_SPACE</font></td>
<td colspan="5"><font size="-5">USER_VERSION</font></td>
<td colspan="1"><font size="-5">ASIC</font></td>
<td colspan="3"><font size="-5">CPU_VERSION</font></td>
</tr>
<tr align="center">
<td><font size="-1">CPU_ID_HI</font></td>
<td><font size="-1">0x01</font></td>
<td colspan="6"><font size="-5">PMEM_SIZE</font></td>
<td colspan="9"><font size="-5">DMEM_SIZE</font></td>
<td colspan="1"><font size="-5">MPY</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>CPU_VERSION</b></li></td>
<td>: Current CPU version (currently 1)</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>ASIC</b></li></td>
<td>: Defines if the ASIC specific features are enabled in the current openMSP430 implementation.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>USER_VERSION</b></li></td>
<td>: Reflects the value defined in the <b>openMSP430_defines.v</b> file.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>PER_SPACE</b></li></td>
<td>: Peripheral address space for the current implementation (byte size = PER_SPACE*512)</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>MPY</b></li></td>
<td>: This bit is set if the hardware multiplier is included in the current implementation</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>DMEM_SIZE</b></li></td>
<td>: Data memory size for the current implementation (byte size = DMEM_SIZE*128)</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>PMEM_SIZE</b></li></td>
<td>: Progam memory size for the current implementation (byte size = PMEM_SIZE*1024)</td>
</tr>
</table>
<a name="2.2.2 CPU_CTL"></a>
<h3>2.2.2 CPU_CTL</h3>
This 8 bit read-write register is used to control the CPU and to configure some basic debug features. After a POR, this register is set to 0x00.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">CPU_CTL</font></td>
<td><font size="-1">0x02</font></td>
<td><font size="-5">Res.</font></td>
<td><font size="-5">CPU_RST</font></td>
<td><font size="-5">RST_BRK_EN</font></td>
<td><font size="-5">FRZ_BRK_EN</font></td>
<td><font size="-5">SW_BRK_EN</font></td>
<td><font size="-5">ISTEP</font></td>
<td><font size="-5">RUN</font></td>
<td><font size="-5">HALT</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>CPU_RST</b></li></td>
<td>: Setting this bit to 1 will activate the PUC reset. Setting it back to 0 will release it.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>RST_BRK_EN</b></li></td>
<td>: If set to 1, the CPU will automatically break after a PUC occurrence.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>FRZ_BRK_EN</b></li></td>
<td>: If set to 1, the timers and watchdog are frozen when the CPU is halted.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>SW_BRK_EN</b></li></td>
<td>: Enables the software breakpoint detection.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>ISTEP</b><sup>1</sup></li></td>
<td>: Writing 1 to this bit will perform a single instruction step if the CPU is halted.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>RUN</b><sup>1</sup></li></td>
<td>: Writing 1 to this bit will get the CPU out of halt state.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>HALT</b><sup>1</sup></li></td>
<td>: Writing 1 to this bit will put the CPU in halt state.</td>
</tr>
</table>
<br /><sup>1</sup>:this field is write-only and always reads back 0.
<br />
<a name="2.2.3 CPU_STAT"></a>
<h3>2.2.3 CPU_STAT</h3>
This 8 bit read-write register gives the global status of the debug interface. After a POR, this register is set to 0x00.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">CPU_STAT</font></td>
<td><font size="-1">0x03</font></td>
<td><font size="-5">HWBRK3_PND</font></td>
<td><font size="-5">HWBRK2_PND</font></td>
<td><font size="-5">HWBRK1_PND</font></td>
<td><font size="-5">HWBRK0_PND</font></td>
<td><font size="-5">SWBRK_PND</font></td>
<td><font size="-5">PUC_PND</font></td>
<td><font size="-5">Res.</font></td>
<td><font size="-5">HALT_RUN</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>HWBRK3_PND</b></li></td>
<td>: This bit reflects if one of the Hardware Breakpoint Unit 3 status bit is set (i.e. BRK3_STAT≠0).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>HWBRK2_PND</b></li></td>
<td>: This bit reflects if one of the Hardware Breakpoint Unit 2 status bit is set (i.e. BRK2_STAT≠0).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>HWBRK1_PND</b></li></td>
<td>: This bit reflects if one of the Hardware Breakpoint Unit 1 status bit is set (i.e. BRK1_STAT≠0).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>HWBRK0_PND</b></li></td>
<td>: This bit reflects if one of the Hardware Breakpoint Unit 0 status bit is set (i.e. BRK0_STAT≠0).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>SWBRK_PND</b></li></td>
<td>: This bit is set to 1 when a software breakpoint occurred. It can be cleared by writing 1 to it.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>PUC_PND</b></li></td>
<td>: This bit is set to 1 when a PUC reset occured. It can be cleared by writing 1 to it.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>HALT_RUN</b></li></td>
<td>: This read-only bit gives the current status of the CPU:
</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 0 - CPU is running.
<br /> 1 - CPU is stopped.
</td>
</tr>
</table>
<a name="2.3 Memory Access Registers"></a>
<div style="text-align: right"><a href="#TOC">Top</a></div>
<h2>2.3 Memory Access Registers</h2>
The following four registers enable single and burst read/write access to both CPU-Registers and full memory address range.
<br />In order to perform an access, the following sequences are typically done:
<ul>
<li>single read access (MEM_CNT=0):</li>
<ol>
<li>set MEM_ADDR with the memory address (or register number) to be read</li>
<li>set MEM_CTL (in particular RD/WR=0 and START=1)</li>
<li>read MEM_DATA</li>
</ol>
<li>single write access (MEM_CNT=0):</li>
<ol>
<li>set MEM_ADDR with the memory address (or register number) to be written</li>
<li>set MEM_DATA with the data to be written</li>
<li>set MEM_CTL (in particular RD/WR=1 and START=1)</li>
</ol>
<li>burst read/write access (MEM_CNT≠0):</li>
<ul>
<li>burst access are optimized for the communication interface used (i.e. for the UART).
The burst sequence are therefore described in the corresponding section (<a href="#3.4 Read/Write burst implementation for the CPU Memory access">3.4 Read/Write burst implementation for the CPU Memory access</a>)</li>
</ul>
</ul>
<a name="2.3.1 MEM_CTL"></a>
<h3>2.3.1 MEM_CTL</h3>
This 8 bit read-write register is used to control the Memory and CPU-Register read/write access. After a POR, this register is set to 0x00.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">MEM_CTL</font></td>
<td><font size="-1">0x04</font></td>
<td colspan="4"><font size="-5">Reserved</font></td>
<td><font size="-5">B/W</font></td>
<td><font size="-5">MEM/REG</font></td>
<td><font size="-5">RD/WR</font></td>
<td><font size="-5">START</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>B/W</b></li></td>
<td>: 0 - 16 bit access.</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 1 - 8 bit access (not valid for CPU-Registers).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>MEM/REG</b></li></td>
<td>: 0 - Memory access.</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 1 - CPU-Register access.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>RD/WR</b></li></td>
<td>: 0 - Read access.</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 1 - Write access.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>START</b></li></td>
<td>: 0- Do nothing</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 1 - Initiate memory transfer.</td>
</tr>
</table>
<a name="2.3.2 MEM_ADDR"></a>
<h3>2.3.2 MEM_ADDR</h3>
This 16 bit read-write register specifies the Memory or CPU-Register address to be used for the next read/write transfer. After a POR, this register is set to 0x0000.
<br />
<strong>Note:</strong> in case of burst (i.e. MEM_CNT≠0), this register specifies the first address of the burst transfer and will be incremented automatically as the burst goes (by 1 for 8-bit access and by 2 for 16-bit access).
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1">15</font></td><td><font size="-1">14</font></td>
<td><font size="-1">13</font></td><td><font size="-1">12</font></td>
<td><font size="-1">11</font></td><td><font size="-1">10</font></td>
<td><font size="-1"> 9</font></td><td><font size="-1"> 8</font></td>
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">MEM_ADDR</font></td>
<td><font size="-1">0x05</font></td>
<td colspan="16"><font size="-5">MEM_ADDR[15:0]</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>MEM_ADDR</b></li></td>
<td>: Memory or CPU-Register address to be used for the next read/write transfer.</td>
</tr>
</table>
<a name="2.3.3 MEM_DATA"></a>
<h3>2.3.3 MEM_DATA</h3>
This 16 bit read-write register specifies (wr) or receive (rd) the Memory or CPU-Register data for the the next transfer. After a POR, this register is set to 0x0000.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1">15</font></td><td><font size="-1">14</font></td>
<td><font size="-1">13</font></td><td><font size="-1">12</font></td>
<td><font size="-1">11</font></td><td><font size="-1">10</font></td>
<td><font size="-1"> 9</font></td><td><font size="-1"> 8</font></td>
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">MEM_DATA</font></td>
<td><font size="-1">0x06</font></td>
<td colspan="16"><font size="-5">MEM_DATA[15:0]</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>MEM_DATA</b></li></td>
<td>: if MEM_CTL.WR - data to be written during the next write transfer.</td>
</tr>
<tr>
<td> </td><td> </td>
<td> if MEM_CTL.RD - updated with the data from the read transfer</td>
</tr>
</table>
<a name="2.3.4 MEM_CNT"></a>
<h3>2.3.4 MEM_CNT</h3>
This 16 bit read-write register controls the burst access to the Memory or CPU-Registers. If set to 0, a single access will occur, otherwise, a burst will be performed. The burst being optimized for the communication interface, more details are given <a href="#3.4 Read/Write burst implementation for the CPU Memory access">there</a>. After a POR, this register is set to 0x0000.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1">15</font></td><td><font size="-1">14</font></td>
<td><font size="-1">13</font></td><td><font size="-1">12</font></td>
<td><font size="-1">11</font></td><td><font size="-1">10</font></td>
<td><font size="-1"> 9</font></td><td><font size="-1"> 8</font></td>
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">MEM_CNT</font></td>
<td><font size="-1">0x07</font></td>
<td colspan="16"><font size="-5">MEM_CNT[15:0]</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>MEM_CNT</b></li></td>
<td>: =0 - a single access will be performed with the next transfer.</td>
</tr>
<tr>
<td> </td><td> </td>
<td> ≠0 - specifies the burst size for the next transfer (i.e number of data access). This field will be automatically decremented as the burst goes.</td>
</tr>
</table>
<a name="2.4 Hardware Breakpoint Unit Registers"></a>
<div style="text-align: right"><a href="#TOC">Top</a></div>
<h2>2.4 Hardware Breakpoint Unit Registers</h2>
Depending on the <a href="http://www.opencores.org/project/openmsp430/core#2.1.3 Configuration">defines</a> located in the "openmsp430_defines.v" file, up to four hardware breakpoint units can be included in the design. These units can be individually controlled with the following registers.
<a name="2.4.1 BRKx_CTL"></a>
<h3>2.4.1 BRKx_CTL</h3>
This 8 bit read-write register controls the hardware breakpoint unit x. After a POR, this register is set to 0x00.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">BRKx_CTL</font></td>
<td><font size="-1">0x08, 0x0C, 0x10, 0x14</font></td>
<td colspan="3"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_MODE</font></td>
<td><font size="-5">INST_EN</font></td>
<td><font size="-5">BREAK_EN</font></td>
<td colspan="2"><font size="-5">ACCESS_MODE</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>RANGE_MODE</b></li></td>
<td>: 0 - Address match on BRK_ADDR0 or BRK_ADDR1 (normal mode)</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 1 - Address match on BRK_ADDR0→BRK_ADDR1 range (range mode)
<br /><font color="red"><b>Note</b>: range mode is not supported by the core unless the `DBG_HWBRK_RANGE define is set to 1'b1 in the <i>openMSP430_define.v</i> file.</font></td>
</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>INST_EN</b></li></td>
<td>: 0 - Checks are done on the execution unit (data flow).</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 1 - Checks are done on the frontend (instruction flow).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>BREAK_EN</b></li></td>
<td>: 0 - Watchpoint mode enable (don't stop on address match).</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 1 - Breakpoint mode enable (stop on address match).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>ACCESS_MODE</b></li></td>
<td>: 00 - Disabled</td>
</tr>
<tr>
<td> </td><td> </td>
<td> 01 - Detect read access.
<br /> 10 - Detect write access.
<br /> 11 - Detect read/write access
<br /><b>Note</b>: '10' & '11' modes are not supported on the instruction flow</td>
</tr>
</table>
<a name="2.4.2 BRKx_STAT"></a>
<h3>2.4.2 BRKx_STAT</h3>
This 8 bit read-write register gives the status of the hardware breakpoint unit x. Each status bit can be cleared by writing 1 to it. After a POR, this register is set to 0x00.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">BRKx_STAT</font></td>
<td><font size="-1">0x09, 0x0D, 0x11, 0x15</font></td>
<td colspan="2"><font size="-5">Reserved</font></td>
<td><font size="-5">RANGE_WR</font></td>
<td><font size="-5">RANGE_RD</font></td>
<td><font size="-5">ADDR1_WR</font></td>
<td><font size="-5">ADDR1_RD</font></td>
<td><font size="-5">ADDR0_WR</font></td>
<td><font size="-5">ADDR0_RD</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>RANGE_WR</b></li></td>
<td>: This bit is set whenever the CPU performs a write access within the BRKx_ADDR0→BRKx_ADDR1 range (valid if RANGE_MODE=1 and ACCESS_MODE[1]=1).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>RANGE_RD</b></li></td>
<td>: This bit is set whenever the CPU performs a read access within the BRKx_ADDR0→BRKx_ADDR1 range (valid if RANGE_MODE=1 and ACCESS_MODE[0]=1).
<br /><font color="red"><b>Note</b>: range mode is not supported by the core unless the `DBG_HWBRK_RANGE define is set to 1'b1 in the <i>openMSP430_define.v</i> file.</font></td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>ADDR1_WR</b></li></td>
<td>: This bit is set whenever the CPU performs a write access at the BRKx_ADDR1 address (valid if RANGE_MODE=0 and ACCESS_MODE[1]=1).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>ADDR1_RD</b></li></td>
<td>: This bit is set whenever the CPU performs a read access at the BRKx_ADDR1 address (valid if RANGE_MODE=0 and ACCESS_MODE[0]=1).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>ADDR0_WR</b></li></td>
<td>: This bit is set whenever the CPU performs a write access at the BRKx_ADDR0 address (valid if RANGE_MODE=0 and ACCESS_MODE[1]=1).</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>ADDR0_RD</b></li></td>
<td>: This bit is set whenever the CPU performs a read access at the BRKx_ADDR0 address (valid if RANGE_MODE=0 and ACCESS_MODE[0]=1).</td>
</tr>
</table>
<a name="2.4.3 BRKx_ADDR0"></a>
<h3>2.4.3 BRKx_ADDR0</h3>
This 16 bit read-write register holds the value which is compared against the address value currently present on the program or data address bus. After a POR, this register is set to 0x0000.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Address</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1">15</font></td><td><font size="-1">14</font></td>
<td><font size="-1">13</font></td><td><font size="-1">12</font></td>
<td><font size="-1">11</font></td><td><font size="-1">10</font></td>
<td><font size="-1"> 9</font></td><td><font size="-1"> 8</font></td>
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">BRKx_ADDR0</font></td>
<td><font size="-1">0x0A, 0x0E, 0x12, 0x16</font></td>
<td colspan="16"><font size="-5">BRK_ADDR0[15:0]</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>BRK_ADDR0</b></li></td>
<td>: Value compared against the address value currently present on the program or data address bus.</td>
</tr>
</table>
<a name="2.4.4 BRKx_ADDR1"></a>
<h3>2.4.4 BRKx_ADDR1</h3>
This 16 bit read-write register holds the value which is compared against the address value currently present on the program or data address bus. After a POR, this register is set to 0x0000.
<br /><br />
<table border="1">
<tr align="center">
<td rowspan="2" ><b><font size="-1">Register Name</font></b></td>
<td rowspan="2" ><b><font size="-1">Addresses</font></b></td>
<td colspan="16"><b><font size="-1">Bit Field</font></b></td>
</tr>
<tr align="center">
<td><font size="-1">15</font></td><td><font size="-1">14</font></td>
<td><font size="-1">13</font></td><td><font size="-1">12</font></td>
<td><font size="-1">11</font></td><td><font size="-1">10</font></td>
<td><font size="-1"> 9</font></td><td><font size="-1"> 8</font></td>
<td><font size="-1"> 7</font></td><td><font size="-1"> 6</font></td>
<td><font size="-1"> 5</font></td><td><font size="-1"> 4</font></td>
<td><font size="-1"> 3</font></td><td><font size="-1"> 2</font></td>
<td><font size="-1"> 1</font></td><td><font size="-1"> 0</font></td>
</tr>
<tr align="center">
<td><font size="-1">BRKx_ADDR1</font></td>
<td><font size="-1">0x0B, 0x0F, 0x13, 0x17</font></td>
<td colspan="16"><font size="-5">BRK_ADDR1[15:0]</font></td>
</tr>
</table>
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>BRK_ADDR1</b></li></td>
<td>: Value compared against the address value currently present on the program or data address bus.</td>
</tr>
</table>
<a name="3. Debug Communication Interface: UART"></a>
<div style="text-align: right"><a href="#TOC">Top</a></div>
<h1>3. Debug Communication Interface: UART</h1>
With its UART interface, the openMSP430 debug unit can communicate with the host computer using a simple RS232 cable (connected to the <a href="http://www.opencores.org/project/openmsp430/core#2.1.4 Pinout">dbg_uart_txd</a> and <a href="http://www.opencores.org/project/openmsp430/core#2.1.4 Pinout">dbg_uart_rxd</a> ports of the IP).<br />
Using an standard <a href="http://www.google.com/search?q=usb+to+rs232+converter">USB to RS232 adaptor</a>, the interface provides a reliable communication link up to 1,5Mbps.
<a name="3.1 Serial communication protocol: 8N1"></a>
<h2>3.1 Serial communication protocol: 8N1</h2>
There are plenty tutorials on Internet regarding RS232 based protocols. However, here is quick recap about 8N1 (1 Start bit, 8 Data bits, No Parity, 1 Stop bit):<br />
<br />
<img src="getimg.php?1247419201" alt="8N1 Serial Protocol" title="8N1 Serial Protocol" />
<br />
As you can see in the above diagram, data transmission starts with a Start bit, followed by the data bits (LSB sent first and MSB sent last), and ends with a "Stop" bit.
<a name="3.2 Synchronization frame"></a>
<h2>3.2 Synchronization frame</h2>
After a POR, the Serial Debug Interface expects a synchronization frame from the host computer in order to determine the communication speed (i.e. the baud rate).<br />
The synchronization frame looks as following:
<br />
<img src="getimg.php?1247420610" alt="Debug Synchronization Frame" title="Debug Synchronization Frame" />
<br />
As you can see, the host simply sends the 0x80 value. The openMSP430 will then measure the time between the falling and rising edge, divide it by 8 and automatically deduce the baud rate it should use to properly communicate with the host.
<br /><br />
<b>Important note</b>: if you want to change the communication speed between two debugging sessions, the openMSP430 needs to go over a POR cycle and a new synchronization frame needs to be send.
<a name="3.3 Read/Write access to the debug registers"></a>
<h2>3.3 Read/Write access to the debug registers</h2>
In order to perform a read / write access to a debug register, the host needs to send a command frame to the openMSP430.<br />
In case of write access, this command frame will be followed by 1 or 2 data frames and in case of read access, the openMSP430 will send 1 or 2 data frames after receiving the command.
<a name="3.3.1 Command Frame"></a>
<h3>3.3.1 Command Frame</h3>
The command frame looks as following:
<br />
<img src="getimg.php?1247427400" alt="Debug Command Frame" title="Debug Command Frame" />
<br />
<table border="0">
<tr>
<td> </td><td valign="top"><li><b>WR</b></li></td>
<td>: Perform a Write access when set. Read otherwise.</td>
</tr>
<tr>
<td> </td><td valign="top"><li><b>B/W</b></li></td>
<td>: Perform a 8-bit data access when set (one data frame). 16-bit otherwise (two data frame).<tr>
</tr>
<tr>
<td> </td><td valign="top"><li><b>Address</b></li></td>
<td>: Debug register address.<tr>
</tr>
</table>
<a name="3.3.2 Write access"></a>
<h3>3.3.2 Write access</h3>
A write access transaction looks like this:
<br />
<img src="getimg.php?1247428987" alt="Debug Write Transaction" title="Debug Write Transaction" />
<a name="3.3.3 Read access"></a>
<h3>3.3.3 Read access</h3>
A read access transaction looks like this:
<br />
<img src="getimg.php?1247429086" alt="Debug Read Transaction" title="Debug Read Transaction" />
<a name="3.4 Read/Write burst implementation for the CPU Memory access"></a>
<h2>3.4 Read/Write burst implementation for the CPU Memory access</h2>
In order to optimize the data burst transactions for the UART, read/write access are not done by reading or writing the MEM_DATA register.<br />
Instead, the data transfer starts immediately after the MEM_CTL.START bit has been set.
<a name="3.4.1 Write Burst access"></a>
<h3>3.4.1 Write Burst access</h3>
A write burst transaction looks like this:
<br />
<img src="getimg.php?1247430408" alt="Debug Write Burst Transaction" title="Debug Write Burst Transaction" />
<a name="3.4.2 Read Burst access"></a>
<h3>3.4.2 Read Burst access</h3>
A read burst transaction looks like this:
<br />
<img src="getimg.php?1247430449" alt="Debug Read Burst Transaction" title="Debug Read Burst Transaction" />
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