Pi 4, 8GB RAM, 64-bit OS...

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https://www.raspberrypi.org/blog/8gb-raspberry-pi-4-on-sale-now-at-75/

https://www.raspberrypi.org/forums/viewtopic.php?f11%7&t27%5370

-Gordon

Re: Pi 4, 8GB RAM, 64-bit OS...
On 28/05/2020 11:36, Gordon Henderson wrote:
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That is excellent news.

I wonder if it also includes the necessary assemblers and compilers to  
produce 64 bit programs?

IMHO this will be computing coming of age for the man
on the Clapham Omnibus, for no longer will it be necessary
to program one's way around the limitations of processor design
because with so much memory, take the same design principle
that made Admiral Fisher's Dreadnought battleship design
so capable, big guns only, make all storage, even for
8 bit bytes, 64 bits.

64-bit-only BCPL anybody?


Re: Pi 4, 8GB RAM, 64-bit OS...
On 28/05/2020 12:45, Gareth Evans wrote:
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PS ! ! ! !

Not forgetting that all instructions encode into 32 bits, so
a compiler based on 64 bit data alone will be struggling to
output dollops of 32 bits, perhaps a variation of the PEEK and
POKE so favoured by early domestiv BASICs?


Re: Pi 4, 8GB RAM, 64-bit OS...
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BCPL compiles into a bytecode. This is then interpreted by a
C program (at least on most modern Unix/Linux systems).

There is a native ARM code generator but I've never looked at it.

-Gordon

Re: Pi 4, 8GB RAM, 64-bit OS...
On 28/05/2020 12:49, Gareth Evans wrote:
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I'm afraid this makes no sense at all. Both ARMv7 (32 bit) and ARMv8  
(ARMv8) can handle data of 8, 16, 32, and 64 bit widths.

---druck


Re: Pi 4, 8GB RAM, 64-bit OS...
On 29/05/2020 21:20, druck wrote:
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It makes perfect sense in the context of the discussion about a
Dreadnought language that has ONLY 64 bit variables.



Re: Pi 4, 8GB RAM, 64-bit OS...
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Indeed.

Although I'm not sure I'd describe BCPL as "Dreadnought" - more "light
cruiser" :-)

And now I'm thinking - does the Piv4 (and v3) have a 64-bit data bus, or
does it need 2 memory cycles at 32-bit each to read a 64-bit value. I'd
like to think it has a 64-bit (or wider) databus, but I really don't know.

This is something that's making my retro implementation of BCPL on a
65816 somewhat slower than it might be - the '816 is touted as a 16 bit
CPU, but it's still locked into an 8-bit data bus.

Gordon

Re: Pi 4, 8GB RAM, 64-bit OS...
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All Pis still have a 32 bit wide external DRAM interface, so that aspect
doesn't change, although it goes from LPDDR2 to LPDDR4 on the Pi 4 (so
higher memory bandwidth).

That will feed the last-level cache.  That's shared with the GPU and I'm not
sure if details are public, but as far as the CPU is concerned:
(cut and paste from Arm's descriptions)

Pi 2 v1.0: Cortex A7
Fixed [L2 cache] line length of 64 bytes [512 bits]
The L2 memory system interfaces with an AMBA AXI Coherency Extension (ACE)
interconnect on a 128-bit wide bus.

Pi 3: Cortex A53
512 bit wide fetch path from L2
A single 128-bit wide master interface to external memory

Pi 4: Cortex A72
Fixed [L2 cache] line length of 64 bytes [512 bits]
Configurable 128-bit wide ACE or 128-bit wide CHI interface [to external
memory]

The description of the Pi 1's ARM1176 is confusing as it appears the L2 has
four separate downstream ports, three 64 bit and one 32 bit.  However I
think the best you could do is 64 bit fetches.


So no change across the Pi families, possibly excepting the Pi 1.  As far as
the CPU core is concerned you can make 32, 64 or 128 bit accesses from cache
in a single cycle.  The bottom of the L2 can make 128 bit wide requests from
DDR memory, which will cause a burst of four 32 bit requests back-to-back.
The Pi 4 has LPDDR4-3200, which means those 4 requests will take:

4*(1/(3200*10^6)) = 1.25ns

Generally the setup time for a DRAM is the expensive part, so once you have
the request in the extra cycles for fetching multiple words don't cost much
more.

(I can't seem to find the data sheet for the Pi 4's DRAM part to see what
the initial latency is)

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But you'll presumably win with not burning lots of cycles doing 32 bit
arithmetic.  Although lack of registers will likely be a pain.

Theo

Re: Pi 4, 8GB RAM, 64-bit OS...
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Some interesting details in this thread, look for posts by dom especially:
https://www.raspberrypi.org/forums/viewtopic.php?f63%&t27%1121

Re: Pi 4, 8GB RAM, 64-bit OS...
Got everything working I tried (SAMBA, NTP, SNMP, minicom etc.) and  
installed gpsd from the source (as I wanted the current 3.20, not the  
"ancient" 3.20).  Minor issue to get my own gps monitoring software  
working - write-up here:

   https://www.satsignal.eu/raspberry-pi/UpdatingGPSD.html#64

RPi 4B, 4 GB.  Fast command-line compiles etc.  Noted that the serial  
port changed from ttyAMA0 to ttyS0.
--  
Cheers,
David
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Re: Pi 4, 8GB RAM, 64-bit OS...
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What is the primary and secondary uart changed between the pi 1/2 and 3/4.
ttyS0 was and is the mini-uart, you might not want to use that, or at least
it requires fixing the cpu with core_freq25%0. See
https://www.raspberrypi.org/documentation/configuration/uart.md


Re: Pi 4, 8GB RAM, 64-bit OS...
On 01/06/2020 03:27, A. Dumas wrote:
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Yes, I had forgotten about the mini/PL011 UART issue, not even following  
my own notes!  Thanks for the reminder - I've updated my Web page and  
thanked you there.

--  
Cheers,
David
We've slightly trimmed the long signature. Click to see the full one.
Re: Pi 4, 8GB RAM, 64-bit OS...
On 29/05/2020 22:03, Gareth Evans wrote:
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No, its still gibberish. BASIC and C running on 8 bit machines could  
have 32 bit variables. Having the size of the variable match the size of  
the processors register size is the most efficient combinations, but it  
in no way precludes using larger (or smaller) variables in any language.

---druck



Re: Pi 4, 8GB RAM, 64-bit OS...
On 30/05/2020 22:33, druck wrote:
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That was the problem on 8 bit micros with C - the language guarantees a  
16 bit integer minimum.

even multiplying 8 x 8 bits meant promotion to 16 and a 16 bit result


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--  
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin


Re: Pi 4, 8GB RAM, 64-bit OS...
On 30/05/2020 22:33, druck wrote:
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I think that you have missed the point being made and are
arguing off at a tangent.



Re: Pi 4, 8GB RAM, 64-bit OS...
On Thu, 28 May 2020 12:45:22 +0100, Gareth Evans

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Likely when in a few months the 64-bit OS becomes stable.

Re: Pi 4, 8GB RAM, 64-bit OS...
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64-bit BCPL has been a thing for a long time. Just re-compile the compiler
and you'll have it. Should take all of a second or so.

-Gordon
(BCPL user, but sticking to 32-bit on a 16 bit CPU with an 8-bit memory
bus, for now :-)

Re: Pi 4, 8GB RAM, 64-bit OS...
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It should.  I've run 64-bit Gentoo Linux on the Raspberry Pi 3 before.  
Compiling on-device can be a bit painful (and some of the larger packages,
like Chromium, won't build in 1 GB RAM), but I would build software under
emulation on a more powerful host and sync binary packages over for
installation.

  _/_
 / v \ Scott Alfter (remove the obvious to send mail)
(IIGS( https://alfter.us/ Top-posting!
 \_^_/                              >What's the most annoying thing on Usenet?

Re: Pi 4, 8GB RAM, 64-bit OS...
On 29/05/2020 15:15, Scott Alfter wrote:
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Interesting.

Did the foreign Gentoo Linux provide full video capability and access to  
all the I/O?



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