RetroBSD

2.11BSD operating system for microcontrollers
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PostPosted: Fri May 22, 2015 12:02 pm 
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The SD regulator shall not be used for other peripherals, only for the sdcard socket, it gets "shorted" for a while when inserting micro sdcard (yes, they include mlcc capacitors inside)..
P.

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PostPosted: Fri Jun 12, 2015 1:54 pm 
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I have found an LDO regulator by good-old Microchip that is a drop-in replacement for the existing TI regulator. Double the current handling, and saves on one capacitor per regulator.

That's 300mA for the core, and 300mA for the SD card and any other peripherals you should choose to power from the 3V3P pin.

Means I can use up some of my existing prototype boards before I have to do a redesign.

These regulators also have an open-drain "power good" pin, so I am thinking I may link those both up to the MCLR pin of the MCU so that it remains in reset until the regulators both signal that they are within 95% of 3.3V.

In other news, Microchip have finally agreed to release the Harmony USB stack to the chipKIT project under an Apache license. Their Applications Engineers are going to create us a custom version with just the bits in we need, which should make it reasonably easy to integrate both into chipKIT and, ultimately, into LiteBSD.

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PostPosted: Sat Jun 13, 2015 5:52 am 
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Good news! For LiteBSD, it makes sense to port the USB stack from OpenBSD, using Microchip sources at the hardware level.

FYI: I made a version of classic article "Building BSD Kernels with Config", adapted for LiteBSD and PIC32: https://github.com/sergev/LiteBSD/wiki/Kernel-Config.


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PostPosted: Thu Jun 18, 2015 1:00 pm 
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Hi Serge and all,

Most amazing :). Nice work!

A question: Can this accomodate both MX and MZ cpus?

And it would be nice to have a few real working examples. I think you may have already done this?

I am needing some PIC32 boards for building things as my kludge breadboards are very hard to customize. Maybe its finally PCB time for me?

Not sure how Matt is coming with his MZ design? My MX stuff is working pretty well, so thus the question.

Do I do MX or try to use Matt's MZ?

Lots of fun !! :) :).

Wiz


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PostPosted: Thu Jun 18, 2015 3:28 pm 
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The mx and MZ chips have different power requirements and the power pin arrangement is different

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PostPosted: Thu Jun 18, 2015 5:27 pm 
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Hi Matt,

Different pins. Nice to know.

I am thinking of a PCB with a 'standard' edge connector. The RasbPi B+ sort of. The pin arrangement I have more or less standardized on so far is quite a bit different from B+.

If I get it right, I should be able to plug either an MX or MZ into the 'backplane' and have it work.

Nice theory of course :).

Right now I am sick and tired of either soldering pins in one at a time or plugging headers in and soldering to them.

The boot works well enough so that software could/should be on a plug-in SD.

Just what I am thinking right now.

Lots of fun.

Wiz


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PostPosted: Thu Jun 18, 2015 7:29 pm 
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For years I have been wanting to build up a multi-cpu computer based around pic32 chips. Pluggable modules with a pic32 and different external peripherals all on a DIN whatever it is Euro connector backplane. Each board has all the software needed to operate it on its pic and all the pics communicate through effectively a high speed parallel network on the backplane.

A mix of modern SMP with messaging and old school eurocards :)

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PostPosted: Fri Jun 19, 2015 7:42 am 
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Good idea. Not sure about high speed parallel network, though. How about i2c bus?


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PostPosted: Fri Jun 19, 2015 9:08 am 
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I've never been much of a fan of I2C - it's too slow for my liking. I'd rather transfer, say, 8 bits in parallel, like double-SQI - maybe SOI ;) But with multi-master, collision detection, etc...

Besides, where's the fun in using something someone else has already done?

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PostPosted: Fri Jun 19, 2015 1:15 pm 
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Hi Matt and Serge,

Choice of bus is THE problem. At least in my humble problem.

My bus so far. Power, clock, ground, serial 2 way, data in, data out, selects and other stuff

Where power is CPU voltage compatible, 3.3 in our case.

I have quite a few modules that just plug into this and just work.

The two way serial ( so called half duplex ) allows really cheap stuff to be powered from and talk to 3 pins. I usually use 1200 baud as the base rate. My PIC32 stuff uses 4800 right now. Speed shifting is quite possible but I doubt it is worth the effort?

The clock of spi is 'shielded' by power and ground and also delayed a small bit allowing simple shift registers to just plug in.

The serial i/o can be used to extend the select scheme. communicate simple low bandwidth data, etc.

The selects and other stuff allows ADC inputs, PWM outputs, etc. to be directly available to the plug in modules.

I usually make the minimum 10 pins. Sometimes I add a 2nd row and put +5V on the secondary power pin and define a pin as global reset.

Anyways, you get the idea. Seems to work pretty well here.

I am looking at a 6 slot, single row version of this bus with my RF stuff plugged into it talking to one of my PIC32 kludges :)..

Higher speed stuff is a very good question. I think ethernet in its various speeds fills that need with more or less non-proprietary stuff with 'simple' support software, unlike usb.

I 'should' get one of the Arduino gizmo packages Serge talked about and see if it fits this scheme?

Lots of fun.

Wiz


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PostPosted: Fri Jun 26, 2015 1:28 pm 
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Hi Matt and All,

I forgot to mention one small detail. I usually make the idle state of the half-duplex serial port resistive pull-up to cpu voltage. The reason is that when this is done, a couple of opto isolators can be used by the remote node to 'talk' to the bus while providing dielectric isolation [ground loop blocking]. This is often required when making measurements. And the further note that 3.3V is marginal for this sort of thing since the opto output is often a Darlington transistor.

In any case the complexity and cost is moved from the main board to the remotes.

Wiz


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PostPosted: Sat Jun 27, 2015 1:17 am 
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I think CANBus will be a good choice, we are working on it and hope soon Vak too :roll:

At 1Mbps 40 mts of cable less speed more cable (mmm domotics..) , etc... also can wire up to 127 devices, in theory only limited by capacitance of the transceivers and cables, I wired up more than 60 devices on the same bus on production and it works like a charm !

8 byte payload but in the other hand collision and error management / correction and a very relliable bus (automotive, etc), also then will be possible to add other CANBus enabled devices to the system.... ;)

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PostPosted: Sat Jun 27, 2015 2:59 pm 
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Hi Mike and All,

Can bus has some real advantages :).

My own preference for a somewhat faster bus would be 10base2. The so called cheapernet.

Why?

One wire and ground. No network 'hub' to get hacked. LOTS of stuff around that works with it [old ISA bus cards, etc.]. Provides dielectric isolation.

Being 'half-duplex' a single processor can both send and receive on it. And processors being LOTS faster these days, a single small micro can just talk on it.

I suspect PIC32 can send and receive on it directly? No fancy chips needed, just a few transistors to keep glitches from killing the PIC32. [This is still on my to do list.]

LOTS of experience with it. The only real problem I have with it, and yes I still have it up and running, is that the supplied BNC connectors are NOT long term reliable. I have replaced them with simple screw terminal connections. Gas tight. Work FOREVER.

All that said, am I the last person in the world using it? And even on an old 8086 PC as a production tester.

All that said, the more 'networking' kinds of things we do the better product we will have!!

Wiz


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