Custom Teensy LC with MKL20 and MKL26Z128VFT4 (128kb flash)

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kshitijdadhekar

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Hey guys,
I am designing a custom teensy LC but there code is kinda big with too many variables and I am afraid its exceeding the 64k flash available on the MKL26Z64VFT4 of the Teensy LC. Will the pre-bootloaded MKL02 chip support the MKL26Z128VFT4 which has double the flash -128kb and 16kb sram? If not then please share any workarounds for this scenario. I dont want to use the MK20DX of the Teensy 3.2, it uses too much space on the PCB and is an overkill for my application.

Thanks in advance
 
Per the MKL02 bootloader page (https://www.pjrc.com/store/ic_mkl02.html), it will only support the LC, 3.2,3.5,3.6 but not the 3.0 which is the chip you're interested in. You'll have to use the older MINITAN54 bootloader chip, which is slightly larger than the MKL02.

EDIT: Ooops, I thought you were going for the QFN version of the MK20Dx128 (like one horse here has) rather than the MKL26 series. Your approach will not work out of the box. At the very least, you'll have to come up with a new boards.txt file. There likely will be more and Paul likely will have too much on his plate to help you with supporting a chip for which he ships no products.

Thus, I'd look for the thread where onehorse described making a DIY Teensy with a tiny QFN version of the MK20DX128 chip. That chip needs to use a MINITAN54 boot loading chip. I have previously posted eagle libraries for the minitan 54. I have not posted a library for the QFN version of the '128, perhaps you can get a version from onehorse.

PS: I'm at a loss to explain why "MKL02/MKL04 does not implement Teensy 3.0 or 3.1." as shown here: https://www.pjrc.com/store/ic_mkl02.html . AFAIK, the CPU used on the 3.1 is the same as the CPU used on the 3.2, see https://www.pjrc.com/teensy/teensy31.html, so I wonder if this is a typo on the part of whoever wrote up the MKL02 bootloader page.
 
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I too am planning a future board and wondering if the MKL26Z128VFT4 could be used.
Is it a matter of just redefining storage/RAM as a new board or is it more complicated?

The sketch uses 33Kb (52%) storage, but 7.9Kb (98%) memory with NoUSB. I need two HW serials, have not tried omitting the third. And this doesn't include all code that may be needed, so 25-30% left for future addons would be nice.
Alternatively, is there a known way of expanding/sharing memory with an additional chip?
I would go for the MK20DX256VLH7, but space is scarce and unfortunately they don't offer QFN versions.
 
Fyod said:
wondering if the MKL26Z128VFT4 could be used.
Click to expand...

There's a chance it might work, with only half the flash memory being programmable. But it might not work at all, and since it's unsupported, no fix will be coming. If you have an extra board, maybe solder one up to experiment, with the expectation there's a good chance it'll be a total loss.
 
Thanks, Paul. I understand the pitfalls, although I had luck with the smaller 36pin chip version last time.
Regarding half memory - is this something that a programmer like me with average code experience could fix with a "new board" and looking at the registry definitions, or does it go deeper into the rabbit hole and possibly not worth the time/effort?
 
I found that the MK20DX128 (Teensy 3.0) is also offered in QFN and has all the features I need. (Actually DX256 seems to be made in QFN36 also, but are not stocked anywhere).
The only problem I see when looking at the schematics is that the Mini54 is connected to PTB2, PTB3, which aren't included on the smaller chip.
Can these be ommited? I read on Phillip Schuster's "Custom Teensy" github that they are no longer used, but I couldn't find the forum post he was referencing.
Also, P0.0 is connected to uUSB pin 4. Is there any reason for this? The newer boards don't have this connection either.
 
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