Raspberry Pi BCM2835 ARMv6 support by Fletch

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seb mitchell

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Nov 27, 2015, 5:50:38 AM11/27/15
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I wonder if you could cross compile Fletch for ARMv6 used by the old Raspberry Pi and the new us$5 Zero.

Don't know if this is important for Fletch, but the BCM2835 has Floating Point Unit.

Doing a google I found this article about hard FP cross compiler 

Just wonder Thanks.
Seb



Mads Ager

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Nov 27, 2015, 6:07:10 AM11/27/15
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Hi Seb,

we haven't tried, but off the top of my head I don't see anything in Fletch that would prevent us from running on ARMv6. Most of our code is C++ and should just work giving a working cross-compiler. We have an interpreter that we have handwritten in ARM/Thumb2 assembly. We are not using any complicated instructions at this point and therefore, I don't think we would need to change much (if anything) to get that running on ARMv6.

Cheers,
Mads

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Erik Corry

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Nov 27, 2015, 6:31:39 AM11/27/15
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Should be possible.  Biggest missing things in ARMv6 are

movt and movw - the 16 bit immediate load instructions - use PC-relative loads and constant pools
VFP floating point - use the old floating point instructions instead (if available!)
NEON - but we never used that in any VM anyway

Mostly the assembler takes care of this for us in fletch.

For the GC I want to use a pop count (count the number of 1s in a word), and there's actually a NEON instruction for it, but nothing on ARMv6.  There's some cleverness in Hacker's Delight I can use.


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seb mitchell

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Dec 14, 2015, 7:17:20 AM12/14/15
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If you want a pi zero these guys have stock, don't know for how long.

Michael Thomsen

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Dec 14, 2015, 9:28:16 AM12/14/15
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Looks like they are already sold out.

On Mon, Dec 14, 2015 at 1:17 PM, seb mitchell <si...@jseb.com> wrote:
If you want a pi zero these guys have stock, don't know for how long.

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Søren Gjesse

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Dec 15, 2015, 2:44:16 AM12/15/15
to Michael Thomsen, seb mitchell, Fletch Discuss
I we need ARMv6 boards to test with the original Raspberry Pi will work as well.

seb mitchell

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Dec 15, 2015, 2:55:28 AM12/15/15
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True, was thinking if there was an sd card image that supported usb otg, 
then connecting a pi zero to a computer to supply the network would require a simple usb phone cable.

Pi zero would still require 5v power connect to the other usb.
Don't know howmuch work is required to get usb otg networking up and running.

seb mitchell

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Jan 4, 2016, 4:44:45 AM1/4/16
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Just an update on the pi zero.

The pi zero OTG usb port can be used to power the zero and networking at the same time.
Power requirements of the pi zero are 100ma at idle.

To get the ethernet working some modules needed to be added.
http://pi.gbaman.info/?p=699
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