SWD debugging mode of stm32

We often use Jlink Downloader , One drawback of this Downloader is that it is used Jtag 20PIN Interface , Too many PIN Will lead to some small PCB The board is crowded , It will also increase the difficulty of wiring . While using SWD Interface download and debugging , Just use 4 individual PIN:  GND, RST, SWDIO, SWDCLK , And the download speed can reach 10M/s, The advantages are obvious .

SWD Brief description of simulation mode concept

 

One 、SWD It's different from traditional debugging

• SWD Model than JTAG More reliable in high speed mode . In the case of large amounts of data JTAG The download will fail , however SWD It's much less likely to happen . Basic use JTAG In the case of simulation mode, it can be used directly SWD Mode , As long as your emulator supports . So I recommend you to use this mode .

 

• In everyone GPIO Just when one is missing , have access to SWD Simulation , This mode supports fewer pins .

 

• It is recommended to use when the size of the board is limited SWD Pattern , It needs fewer pins , Of course we need to PCB The space is small ！ For example, you can choose a small one 2.54 Spaced 5 The core terminal is used as the simulation interface .

 

 

Two 、 The simulator is right SWD Mode support

 

1. Common simulators on the market are right SWD Mode support

 

        (1) JLINKV6 Support SWD Simulation mode , Slower .

        (2) JLINKV7 Better support SWD Simulation mode , The speed has been significantly improved , The velocity is JLINKV6 Of 6 times . 

        (3) JLINKV8 Very good support SWD Simulation mode , The speed can reach 10M.

        (4) ULINK1 I won't support it SWD Pattern .

        (5) Pirate ULINK2 Very good support SWD Pattern , Speed can reach 10M.

        (6) The original ULINK2 Very good support SWD Pattern , Speed can reach 10M.

 

2. SWD Differences in hardware interfaces

 

        (1) JLINKV6 The required hardware interface is : GND, RST, SWDIO, SWDCLK

        (2) JLINKV7 The required hardware interface is : GND, RST, SWDIO, SWDCLK

        (3) JLINKV8 The required hardware interface is : VCC, GND, RST, SWDIO, SWDCLK （ notes ： Here are some for my own use JLINKV8 And the corresponding experimental results ）

        (4) ULINK1 I won't support it SWD Pattern

        (5) Pirate ULINK2 The required hardware interface is : GND, RST, SWDIO, SWDCLK

        (6) The original ULINK2 The required hardware interface is : GND, RST, SWDIO, SWDCLK

 

    From this we can see that only JLINKV8 need 5 One pin , One more VCC Pin , The advantage is that : The simulation of the target board by the simulator needs RST Pin , Use the inside of the simulator VCC This function is not very wonderful . therefore ,JLINKV8 You have chosen to share only with the target board GND, But not altogether VCC. So I think this model is the most reasonable , Of course, usually the emulator and the target board share GND and VCC There's nothing wrong with it .

 

3、 ... and 、 stay MDK in SWD Mode settings

 

    When debugging the simulation, use J-LINK Of Cortex-M3 The way is enough , And in MDK His function has been done very well , Using standard 20 Foot's JTAG download , The speed is very fast , This is what most beginners do . however SWD The way seems to be faster 、 It is more convenient 、 Simple and direct 、, Strict requirements for board space in the project 、I/O It is more beneficial to users who are short of oral resources , natural JTAG need 20 Pin , and J-Link Of SWD It only needs 2 Root line （PA13/JTMS/SWDIO、PA14/JTCK/SWCLK） That's enough （ Add the power cord 4 root ）, This saves you 3 individual I/O mouth （PA15/JTDI、PB3/JTDO、PB4/JNTRST） For other purposes , And it can save some board space ( just 4 Just take a bite ).

 

    Now let me say something SWD Some steps of two-wire simulation 、 Precautions and problems needing attention .

 

    The interface is connected as follows ： take JLINK Of 1、7、9、20 And their own development boards JTAG Of VCC、JTMS、JTCK、GND Connect with DuPont line ！

 

    Next, let's tell you how to use SWD Set up ：

 

Open the project OPTION Set up ：

 

 

         In the setting, it is set to... According to the above figure SWD Pattern , You can set the speed according to your actual needs , If your board power supply system is not particularly stable , If the ripple is large or the simulation line is long, it can be set to 500K perhaps 1M, If the environment is good, of course you can choose 10M , Of course the speed will fly .

 

    Remember not to ignore the one at the bottom left USB still TCP Pattern , Of course we are USB Pattern , Because sometimes the default is TCP Pattern , At this time, if we ignore this setting, we will simulate that the connection is often unavailable .

 

Press SW Way to debug , Actually, it is necessary to connect 1,7,9,15,20 foot , Some materials say it is necessary 6 A foot （ The first 13 foot SWO It also needs to be connected ） It is not right ,SWO There is no need to connect .

 

my Jilnk and Development board Wiring diagram ：

 

 

• The white line : 3.3v      
• Black line : GND      
• Gray line ：SWIO
• Purple line ：SWCLK

         About whether to connect Reset Pin problem I didn't connect it during the test   It can be downloaded and debugged normally   And the download speed is set to 10Mhz   Still no problem   The speed is really much faster ..