SWD

This introduction provides a general overview of the SWD debugging system.

Using SWD Debug Interface

Users can use SWD debugging with Keil or Jlink Commander.

SWD Hardware

SWD is a hardware interface standard developed by ARM for debugging and programming embedded systems. Compared to the traditional JTAG interface, SWD offers fewer pins, higher performance, and lower power consumption.

RTL87x3E to Jlink Connection

The SWD interface connection is straightforward and involves the following pins: VCC, SWCLK, SWDIO, and GND. These correspond to VDD, CLK, IO, and GND on the EVB (Evaluation Board).

There are four pins to connect to the Jlink - VCC, SWCLK, SWDIO, and GND. These pins correspond to VDD, CLK, IO, and GND on the EVB board.

MCUConfig Tool Settings

P1_0 and P1_1 pins are set to SWDIO and SWCLK, respectively. Therefore, avoid using P1_0 and P1_1 pins in the MCUConfig Tool.

SWD with Keil

Using SWD with Keil μVision is a straightforward process that involves setting up your hardware and configuring the Keil debugging environment. Here’s a step-by-step guide to help you through the process.

Set the Debug Interface

Install the appropriate Jlink driver and then select the corresponding one in Debug Tab of ‘Options for Target…’. We need to choose ‘Jlink / J-trace Cortex’ for RTL87x3E. Then, Disable ‘Load Application at Startup’ which would reset the MCU.

Set the Configuration for Jlink

Make sure the MCU is not in the DLPS state and click the ‘Settings’ button beside the ‘debug driver’. There will be a ‘Cortex Jlink/Jtrace Target Driver Setup’ window.

First, set the port to SWD and speed to 1MHz, and do not choose ‘Reset after Connect’ Then click the Scan Button, and you can see the device name with IDCODE in the SW device. If there is no information in ‘SW device’, please hardware reset the MCU and check the wiring for jlink. By doing so, Keil can find SW device.

Disable the Target Download before Debugging

By default, Keil will download the image through jlink when it starts debugging, so you need to disable the ‘Update Target before Debugging’ option. This option is in the Utilities Tab of ‘Options for Target…’.

Disable Watchdog and DLPS before Build

The purpose of disabling the watchdog is to not reset the MCU when it is halted by SWD. The way to disable the watchdog is as follows.

void system_init(void)
{
	wdg_disable();
	...
}

Make sure the MCU is not in the DLPS state. The way to disable DLPS is as follows.

int main(void)
{
	...
	app_cfg_init();
	...
	app_cfg_const.enable_dlps = 0;
	...
	app_dlps_init();
	...
}

Start a Debug Session during Running

1. Click the ‘Debug’ button to start a Keil debugging session in Keil main window and MCU will be halted.

2. Input the load command as below in the command window.

3. Click the run button and MCU will be halted at the breakpoint.

If there is a pop-up window that mentions that it cannot find ‘SW device’, please reset the MCU and go back to ‘Cortex Jlink/Jtrace Target Driver Setup’ and follow the steps in section 3.2 to check ‘SW device’ information, which means Keil scanned and found ‘SW device’.

Start a Debug from Main Function

For the sake of capturing the MCU before running over the main function, we need to add a delay before the main function. We can add it in system_init of system_rtl8763.c. After pressing the reset key, you need to click Debug to start the simulation as soon as possible. Too fast and it will be too late to identify Jlink, too slow and it will run out of the main function.

1. Reset the MCU and click the ‘Debug’ button to make the MCU halt before main.

2. Input the command ‘LOAD %L INCREMENTAL’ in the command window.

3. Set a breakpoint at the main and click the run button.

Jlink download is not supported, so the modified code needs to be recompiled and returned before debugging. During debugging, the ‘RESET’ button of Keil is not available. Please press the hardware reset on the EVB to start debugging from scratch.

Download with Keil

1. Do Set the Debug Interface and Set the Configuration for Jlink.

2. Copy RTL87x3E_FLASH.FLM in sdk\tool\flash to Keil root directory Keil\ARM\Flash and load the RTL87x3E_FLASH.FLM file as below figure.

3. Download bin with Keil.

SWD with Jlink Commander

Using SWD with Jlink Commander, a command-line utility provided by SEGGER, allows direct communication with the target device for purposes such as flashing, debugging, or performing other operations.

Preparation

This section describes the preparation before starting SWD debugging with Jlink Commander.

Jlink Commander (Jlink.exe) is a command-line-based utility that can be used for verifying the proper functionality of Jlink (the debugger) and for simple analysis of the target system. It supports some simple commands, such as memory dump, halt, step, go, etc. to verify the target connection.

Jlink Commander installation package is packed into https://www.segger.com/downloads/jlink/#JlinkSoftwareAndDocumentationPack. You can click the website and choose the platform you used.

Debug Feature Introduction

There are two categories of debugging methods: invasive debugging and noninvasive debugging.

• Invasive debugging: - Program halt and stepping - Hardware breakpoints - Breakpoint instruction - Data watchpoint on access to data address, address range, or data value - Register value accesses (both read and write) - Debug monitor exception - ROM-based debugging (Flash patch)

• Noninvasive debugging: - Memory accesses (memory contents can be accessed even when the core is running) - Instruction trace (via the optional Embedded Trace Module) - Data trace - Software trace (via the Instrumentation Trace Module) - Profiling (via the Data Watchpoint and Trace Module)

The most common debugging method is invasive debugging, which is used in this guide. So it should be emphasized that you should halt MCU with the command ‘h’ every time you need to read or write registers.

Debug Procedures

1. Debug Configuration:

   In the debugging setting, it needs to set the parameters about the target and debugging sessions.

   1. Start the Jlink commander (by CONNA or desktop shortcut).

   

   2. After Jlink Commander starts, you should use the command ‘connect’ to start the setting for the debugging session.

   

   3. Then you should select the device/core to which the MCU belongs. It is Cortex-M4 for RTL87x3D and Cortex-M3 for RTL87x3E.

   

   

   4. Please specify SWD as the target interface.

   

   5. You can also set the interface speed of SWD. The default speed is 4000kHz, and you can use this value by inputting Enter key directly. It is recommended to be below 2000kHz for debugging stability.

   

   6. Finally, Jlink Commander will print the following information. It means debugging configuration is finished!

   

2. Capture MCU before main: Because the first 32KB in ROM was protected for security, SWD could not halt MCU by its reset command ‘h’. To this limitation, it is difficult to debug the app from the main function directly. It needs to add a dead loop and set PC to the top of the main loop.

   The steps are as follows.

   1. Add a dead loop in system_init in system_rtl8763.c:

   

   2. Connect MCU by following the steps in Debug Configuration.

   3. Halt MCU by ‘h’, and check whether MCU is running in the loop:

   

   4. Set the PC to the top of the main function by the ‘SetPC’ command. Here app’s main function is at 0x831e96:

   

3. Breakpoint Debugging:

   The most commonly used debugging function is breakpoint. In Jlink Command, the breakpoint command is ‘SetBP’. For actual debugging, it should be used in combination with the command ‘go’.

   1. Use SetBP to set a breakpoint in the form of an assembly address. ‘Handle’ is the number used to remove a breakpoint with ClrBP.

   

   2. Input ‘g’ or ‘go’ to make MCU run at full speed. You will see there is no response, but MCU has been halted at the breakpoint you set before. And you can use regs to check this.

   

   3. If you don’t need the breakpoint anymore, ‘ClrBP’ should be used. You will see the hint that Breakpoint is cleared.

   

4. Watchpoint Debugging:

   Watchpoint can be considered as a kind of condition breakpoint. For example, a variable ‘hello’ of type uint8_t is added and it is added in the main while loop as follows.

   1. You can check its address and the code in the .disasm file.

   

   

   2. Set a watchpoint at 0x1000769C for ‘hello’.

   

   3. Let MCU run and it will be halted automatically when ‘hello’ grows up to 5. Check the registers and you will find that 0x8322DE is near 0x8322D4. 0x8322DE is the place MCU writes the value back to 0x1000769C.

   

   

   4. Finally, you can look into the 0x1000769C by ‘mem’:

   

5. Single Step Debugging:

   The single-step debugging command is ‘s’. If you want to single step through your program, you should halt MCU by ‘h’ first. Then you are enabled to go through the program step by step with ‘s’.

   

Common Commands

1. connect
   Syntax: connect
   This command is not listed in the commands help list. As depicted in Debug Configuration, it starts the setting for the debugging session. It is always the first step when using the SWD to debug.

2. h
   Syntax: h
   ’h’ means halt, which will stop MCU. It’s a common command in MCU debugging.

3. s
   Syntax: s
   Single step the target chip.

4. mem, mem8, mem16, mem32
   Syntax:
   mem Addr, NumBytes
   mem8 Addr, NumBytes
   mem16 Addr>, NumBytes
   mem32 Addr, NumBytes
   All these commands are used to read the memory. Both ‘mem’ and ‘mem32’ are the most common commands. ‘mem’ can read the memory with arbitrary size and ‘mem32’ can read the memory with the unit of one word in ARM.

5. w1, w2, w4
   Syntax:
   w1 Addr, Data
   w2 Addr, Data
   w4 Addr, Data
   These commands can write a value to a certain address.

6. q
   Syntax: q
   ’q’ means quit, which can close Jlink Commander.

7. r, rx
   Syntax:
   r
   rx DelayAfterReset
   ’r’ and ‘rx’ can reset the target chip. ‘rx’ can reset the MCU after a specified interval.

8. Regs
   Syntax: Regs
   ’Regs’ is a very common command in almost all command-line debuggers. It can read all the general purpose registers, such as R0-R12, LR, and PC.

9. wreg
   Syntax: wreg RegName, Data
   ’wreg’ can write a value to a specific register.

10. SetBP
    Syntax: SetBP addr
    This command is used to set the breakpoint. It is usually used in combination with the command ‘g’. Command ‘g’ makes MCU run at full speed and if it reaches the breakpoint, MCU can be suspended by Jlink.

11. ClrBP
    Syntax: ClrBP BP_Handle
    This command is used to clear breakpoints which you don’t need anymore.

12. SetPC
    Syntax: SetPC Addr
    This command can set the current PC to a specified address.