Author Topic: Faster CMSIS DAP compatable boards?  (Read 549 times)

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Offline tmadness

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Faster CMSIS DAP compatable boards?
« on: June 15, 2021, 06:34:42 pm »
I've been on the search for a good low cost generic debug probe for a while now. And through trial and error I've come to really like the CMSIS DAP + pyOCD combo.
I've used a number of CMSIS DAP compatible probes like the NXP MCU Link, seeeduino xiao  etc.
Does anyone know of other good quality + higher speed DAPs?
 
 

Online SiliconWizard

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Re: Faster CMSIS DAP compatable boards?
« Reply #1 on: June 15, 2021, 06:59:54 pm »
I just received 2 nanodap-hs probes. Contrary to most cheap CMSIS DAP probes out there, they support USB HS. They are much faster.
(Can be found from MuseLab on Aliexpress.)
 

Online ataradov

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Re: Faster CMSIS DAP compatable boards?
« Reply #2 on: June 15, 2021, 07:07:19 pm »
From readily and widely available devices LPC-Link2 with CMSIS-DAP firmware is the fastest from all I tried. It is the only debugger I have that uses 1024 byte endpoints.

But yes, generally you get enough of a performance boost by switching from FS to HS, that details of the HS implementation almost do not matter. So look for USB HS devices and ignore everything that is FS. There is no reason to compare FS devices between themselves, they all will be slow.
Alex
 

Offline tmadness

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Re: Faster CMSIS DAP compatable boards?
« Reply #3 on: June 15, 2021, 07:31:35 pm »
interesting  they the use ATSAM3U2C, I bought a couple, but I'm not looking forward to shipping...
LPC-Link2 uses DAP I i think, I did not realize that it may have been the fastest, makes sense though it is a dual core MCU running at 150 MHz. Mine just quit on me one day. It's probably from all the mishandling with no container to protect it   >:D.
I just remember that the NXP MCU link at weird quirk, it would randomly reset the target every ~20 min if left idle but connected. It caused some deep consternation and frustration as I tried to debug the issue thinking it was something to do with the code I had written.
 
« Last Edit: June 15, 2021, 07:42:41 pm by tmadness »
 

Online SiliconWizard

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Re: Faster CMSIS DAP compatable boards?
« Reply #4 on: June 15, 2021, 07:42:24 pm »
The LPC-Link2 is cheap and works well? Drawback with the nanodap-hs probes is that they only support 3.3V. No level shifting of any kind as far as I've seen. Not sure about the LPC-Link2 for this?
 

Online ataradov

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Re: Faster CMSIS DAP compatable boards?
« Reply #5 on: June 15, 2021, 08:17:05 pm »
LPC-Link2 has level shifters.

It also has 20-pin trace connector with trace pins actually going to the MCU. I'm not sure how well that works though, I suspect not well at all, given that trace is hit or miss even on dedicated trace probes.
« Last Edit: June 15, 2021, 08:28:51 pm by ataradov »
Alex
 

Offline josip

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Re: Faster CMSIS DAP compatable boards?
« Reply #6 on: June 16, 2021, 05:54:02 am »
BTW, NXP MCU-Link (10$) is based on LPC55S69, dual core Cortex-M33 150 MHz with HS USB and level shifters.
 

Offline tmadness

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Re: Faster CMSIS DAP compatable boards?
« Reply #7 on: June 16, 2021, 06:52:54 pm »
The Link2 has the LPC4370 3 cores: 1X M4, 2X M0 @ 205 MHz :phew: .
As ataradov said it has level shifters on board.
The LPC4370  is actually a really cool part, but they had to handicap it by giving 1 SPI |O
As far as DAP is concerned I would not be surprised if they are running on only 1 core  :-DD
 

Online ataradov

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Re: Faster CMSIS DAP compatable boards?
« Reply #8 on: June 16, 2021, 07:08:55 pm »
DAP does not need the performance, so yes, I would not expect multi-core stuff to matter.

USB HS is the critical part. FS limits the speed at 64 KByte/sec and really bad turnaround time.
Alex
 

Online SiliconWizard

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Re: Faster CMSIS DAP compatable boards?
« Reply #9 on: June 16, 2021, 07:39:27 pm »
DAP does not need the performance, so yes, I would not expect multi-core stuff to matter.

USB HS is the critical part. FS limits the speed at 64 KByte/sec and really bad turnaround time.

Yes of course. Since it's HID, yes it tops at 64 KBytes/s in FS. I don't remember in HS if there's a lower limit for HID or if you can get the full throughput, but either way, it's much faster.

And of course, you don't need a powerful MCU to handle DAP. You just need one that can be clocked fast enough so that the serial clock will be high enough.
As a quick calculation, if it uses SPI or similar for the JTAG/SWD interface, you may typically need a peripheral clocked at a multiple of the max serial rate (2, or 4 times is typical), so, for a 30MHz link, for instance, you'll need a peripheral clock of 60MHz or 120MHz. Depending on the architecture, the core clock will be required to be at least this fast as well. So, a MCU running at > 100MHz actually makes sense for a fast DAP link. Multiple cores, OTOH, are likely completely useless. Anyway, CMSIS-DAP implementation is open and usually what is used on those boards, and I don't think it supports multi-core anyway.

The Link2 probably uses this particular chip because they use it on some other dev boards as well.
 


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