N900 is a great Phone. But i miss some features: better battery, faster browser, less lag.
Better battery is kind of easy. (Yes your device gets more bulky.)
The main reason for the others is i guess lag of ram and bad io.
So if my device gets more bulky by battery, maybe i can fix the other issues too.

First Why not use usb?
sd seems to be the better bus cause it offers lower latency, it can operate at 3.3V and maybe 1.8V, doesnt consume as much power no need for 5V and is supported as an tested addon in N900 and maemo.

So my idea was to get a ram based sd card. to get the most of the sdio bus.

For that i got an bbb, which is kind of the older brother of n900 cpu wise, very familiar.
It has kind of a dual cortex m0 coprocessor running at 200 Mhz. (awesome).
So you can use it as a logic analyser currently able to capture at 100Mhz (my guess is 200 is possible if ti hasnt messed this up too)
to a 380mb of ram. That would be a nice swap space or a nice little nand read only expansion.

So i started my RamOnSD project, to explore what is possible and maybe later use a beagle core to actually expand the n900.
It basicly bitbangs sdio / emulates an sdcard. My initial goal was to get it at 50Mhz 4 lines,
which would give you a 15-18mb random(!) read write card.

I failed, but i blame ti
the current status is i can send at 35mhz (13mbs) zeros via 4bit sdbus.
zeroes are easy cause crc is zero too.
But i know know that i wont reach 50 Mhz mainly because i got an too high latency.
I measured 4 clocks from fast pru output to pru fast input.
But the real problem is pinmuxing..
pinmuxing is a mess on bbb. (Many new technologies: device tree, with many bugs, you are beta tester in this field)
A ti selling point of the prus is bitbanging. But you cant switch the pins from the pru (Bug??),
which leads to nondeterministic latency by going through the a8. You need 3 pins to implement a 1 pin tristate,
the ti easy solution with 2 pins didnt work for me.
For sd you need 5 bidirectonal lines, 1 is the cmd line which needs to be exactly switched in 2 sdbuscyles from input<->output
you cant do that without additional hardware, which adds another 2-4 cycles latency.
At 50Mhz sdbus speed you got 4 cpu cycles per sdbusclock..
You can use the second pru to help. But my guess it would be really hard to bitbang at 50 Mhz.
(the most max value i read in the docs is 25mhz)
I bought additional hardware 1euro bus driver and im now able to send zeros at 35Mhz, 13 mbs.
To send something else you need to fetch it to pru first and then clock it out. Which most likely slows it down more.
So it is a ton of work in minefield. You can read a few problems at beaglelogics status updates how he switched from bbb to ti remoteproc,
just to get some nice features of the pru, which are currently not available on bbb disto. (xin/xout, iloop ..)
(So in my opinion ti failed to push upstream.)

A Picture of my set setup.
http://www.pic-upload.de/view-290104...25053.jpg.html

A samsung/sandisk card can give you already 5 mbs random read.

So second idea: connect a som/soc through sd io, reduce the apps on n900 to basic stuff put this in a ramdisk and do other ram intense thinks (like a browser) on soc/som.

using an fpga for 50 mhz would be too easy more costly and i guess to power hungry.

So some thoughts about possible expansions soc:

Most space is going in for battery so i want a really small form factor. 5.5 x 5.5 cm will fit below camera.

Most problems with soc is powerconsumption. You are limited to <1 watt if you want to power it via N900) I may be wrong on this numbers but i meassured something about that on the sd bus and it matched with the max usb host mode values.
working suspend resume!

community support and recent drivers

linux

affordable

Some possible candidates:

intel edison
+x86 browsers
+ kind of powerful compared to n900
octane score 1000
- community unfriendly
you need an break out to do something
closed source parts
kernel 3.14?
- intel
power consumption:
standby min 13 mW (35 mW with wifi)
max <1W



beagle core
+ ti,bbb in small kind of known community
- unknown powerconsumption for core
- powerconsumption for bbb
suspend 0.1W without ethernet and hdmi
(https://e2e.ti.com/support/arm/sitar...f/791/t/374553)
3 hours on idle, 1400 / 3 ~ 500 ma => 1500 mW
(http://www.element14.com/community/c...battery-system)
- ti
octane score 800 (bbb)

rasberry pi zero
+ linux desktop in pocket
- a laggy linux in your pocket?
+ cheap
- too long in size
power consumption:
no standby (=idle)
ide 100ma at 5V = 0.5W = 500mW
(https://github.com/geerlingguy/raspb...er-Consumption or http://raspi.tv/2015/raspberry-pi-ze...r-measurements)

acqua a5
+ i like the openess of that device, it seems very friendly
+ you can get still a linux kernel 4.2 image for the older g25
? 526 mhz a5 maybe slow but 850 dmips is hopefully in the n900 ballpark
and it appears to have a hardware double precission fpu which should be 3 times as fast a8 and has 512mb
- only the version without l2 cache and neon is used on Acqua
+ atmel seems to push upstream
power consumption:
standby 33ma at 3.3V = 100mW
(https://groups.google.com/forum/#!to...ms/x2XbyutjHVA) (sadly no lpddr option witch would reduce power consumption to a 1/3 according to atmel)
ide 100ma at 3.3V = 0.33W = 330mW
max power consumption 500mw
- seems to be slower than even the rasberry pi zero


second n900
+ own battery
+ case
+ great device
- end of life n900 getting rare
- covers camera, maybe another slider
- no dp floating point unit
- recent kernel with power management is thankfully(!) worked on
but slowly
power consumption on kernel 2.6:
https://wiki.maemo.org/N900_Hardware_Power_Consumption
on 4.2:
6 hours on idle, 1400 / 6 ~ 250 ma => 800 mW
(http://talk.maemo.org/showpost.php?p...87&postcount=8)
suspend unknown

fun candidates:
ga144
+ very powerefficient
+ 144 700 Mhz cpus no floating point on these
+ forth
- maybe missing some memory
- limited io
- browser has yet to be written

The field looks very sparse for mainly a linux/browser on chip
Does anyone know other possible devices, or has experience with the acqua a5 or atmel?

I need to see if n900 supports somehow spi sd cards that would make connecting more easy. But as said in another thread my gsm is gone again. So i have to adress that first before i make improvements.

You have an SMD REWORK STATION
and you are not yet selling n900 clones ? Aghast ye mates !

Will stay tuned to this idea for some time to come...

More fun n900 booting debian900 via BBBSD

BBBSDdebian900Boot.m4v

i had to cheat cause uboot follows the spec more than the cards values and assumes 25MHZ while i report 400khz.
kernel comes from mmc.

time to login after first BBBSD access 6:37 min
login takes around 30 sec.

i couldnt find enough fast pins so i went for 1 bit sdio at 400 khz giving a random io of around 14kb/s

single block read, multi block write working
(they saved single block writes as fallback as well as crc7 check on cmd (so did I))

Does anyone know an sdio device/card/module which works with maemos "old" kernel out of the box. Something like an external wl1251 module? Preferable fast devices (wifi > uart, gps receiver).

Your requested URL has been blocked as per the directions received from Department of Telecommunications, Government of India. Please contact administrator for more information.
What the he*l!

> file-upload.net
Your fascist government blocked the whole website because of single link to some bad (anti-regime?) file. Same as in Russia.
Use VPN or Socks proxy.

Or does someone have a pinout or documentation for wl1251blyfbr?

Seems maemo power53 doesnt have sdio support enabled by default.
MMC_CAP_SDIO seems disabled and
/drivers/mmc/core/core.c skips sdio card init.
But it looks like support for polling via cmd52 at last is in kernel.

My DebiaN900 kernel seems to do sdio polling ok.

It is connected via spi. So not a working sdio solution on n900 .