View source for DIY STM32 Programmer (ST-Link/V2-1)

[[Category:STM32]][[Category:STM32 Projects]][[Category:KiCAD]]{{metadesc|Home made ST-Link V2.1}}
[[File:STLink.jpg|thumb|Original ST-Link]]
[[ST-Link]] devices are almost essential when developing software for the [[STM32]] [[MCU]]s.  They are relatively cheap and easily available.

They roughly fall into two different categories.  [[ST]] themselves make a number of them and they all work quite well.

One thing that annoys me with the original ST-Link devices is that the programming header is unlabelled.  This essentially mean that every time I use it I have to Google for the actual pinout.

Also, the ones I've got (the one in the photo to the right) are ST-Link/V2 devices.

Before diving into any further details, credits to Martin from [http://embedblog.eu/ EmbeddedBlog] who went through the same as here.  His project is linked under [[#Miscellaneous Links|Miscellaneous Links]].

{{Clear}}
[[File:STLink-v2 (Chinese knock off).jpg|thumb|Chinese knock off ST-Link/V2]]
There are also a lot of Chinese clones available and while they have some limitations they also work quite well.

Unfortunately these devices are also ST-Link/V2 devices, and they do not have the SWO pin on the header, so any debug trace is impossible.  For flashing and normal debugging they work fine though.

In short, the ST-Link/V2.1 devices offer a few extra features:

# Serial Wire Trace (SWO)
# Virtual serial port
# Mass storage

All features that, while not absolutely essential, does come quite handy.

Another reason for creating my own "programmer" is that I can experiment with using a GigaDevice GD32F103, which are much easier to source at the moment.
== Original ST-Link V2.1 ==

The schematic of the original ST-Link is readily available from the various Nucleo development modules.

[[File:ST-Link V2.1 Original Schematics.png|1000px]]

A bit messy schematics but it'll do.

== Schematics ==

Based on [[ST]]'s original schematics, creating a version using only parts from [[JLCPCB]]'s parts library was easy (and much nicer if I shall say so myself).

[[File:DIY ST-Link V2.1.svg|1000px]]

One thing [[User:Lth|I]] left out was the serial resistors of the programming header.  This might very well come back and bite me in the ass but space is going to be at a premium.

The main difference hardware wise between [[ST-Link/V2]] and [[ST-Link/V2-1]] is the renumeration circuitry:

[[File:ST-Link-V2-1 Renumeration Circuitry.png|600px]]

[[User:Lth|I]] think what is going on there is ensuring the D+ is pulled high through the 1.5 kOhm resistor unless the RENUM signal is forced low.  The voltage divider R4/R5 and R6 are merely there to protect the transistor itself.  While I do understand what they ([[ST]]) are trying to achieve, I would say they could have achieved this much simpler.  IF the D+ was simply permanently pulled high by the 1.5 kOhm resistor, since it is connected to a GPIO pin, this GPIO pin could simply be briefly yanked low at MCU reset.

As for [[MCU]] the original [[ST-Link/V2-1]] uses an [[STM32F103|STM32F103CB]] (128 kB flash).  Since it is well known that STM32F103C8 [[MCU]]s also have 128 kB flash this one should do nicely too.  In this case however, due to the general shortage of [[STM32]] [[MCU]]s, I went with a [[GigaDevice]] [[GD32]] instead.  It should be "compatible" enough for this purpose.

== PCB ==

For hobby projects like this I will usually stick with double-sided PCB.  But in this particular case I wanted this to fit into the aluminium "sleeve" of the Chinese knock off [[ST-Link]] devices, so space was at a premium.  Also, pricing wise there's not much difference these days, so I went for a four layer PCB and kept +3.3V and GND on the two inner layers.

For SMT assembly, [[JLCPCB]] has a minimum size of 20 mm in either direction:

[[File:JLCPCB Assembly Capabilities.png|800px]]

For a [[USB]] stick 20 mm is too wide, so I had to design the PCB with a breakaway part connected with mouse bites.

The final rev. a layout looks like this:

[[File:PCB Layout rev. a.png|800px]]

The [[KiCAD]] 3D model:

[[File:PCB Layout rev. a - 3D model.png|800px]]

== Revision a ==

A quick order to [[JLCPCB]] and within a week I had my first "samples".

<gallery>
File:STM32 Programmer 5 boards top view.jpg
File:STM32 Programmer 5 boards bot view.jpg
File:STM32 Programmer bot view.jpg
File:STM32 Programmer top view.jpg
File:STM32 Programmer broken out.jpg
File:STM32 Programmer broken out top view.jpg
</gallery>

I had to solder the USB connector by hand and it turned out that I was either out of IDC connectors (or couldn't be bothered to search long enough to dig them out of a box), so I used a simple dual-row standard 100 mil header.
{|
|[[File:DIY ST-Link w. USB connector and header.jpg|600px]]
|[[File:DIY St-Link Hooked up.jpg|600px]]
|}
That is "good enough".  For rev. b, I will put 1 mm more spacing between the IDC header and the components - that was a bit tight.

== Firmware ==

To be added

== Testing == 

To be added

== Miscellaneous Links ==

* [https://github.com/lbthomsen/st-link Github Repository of schematics and pcb]
* [https://ipfs.subutai.io/ipfs/QmdjW4GnqhQYZTfS2NhhZkgkSLiP7iwf8XCB8tSt32QCHi/MB1136.pdf NUCLEO-XXXXRX Schematics (includes ST-Link V2.1]
* [http://embedblog.eu/?p=780 BUILDING A CUSTOM ST-LINK V2.1]
* [https://dalaotech.com/2020/03/31/784/ Chinese blog post creating a custom ST-Link]