[Arm-netbook] A minimal A10 SBC

[Neal Peacock]

On 03/28/2013 07:07 AM, luke.leighton wrote:
> On Thu, Mar 28, 2013 at 4:22 AM, Ajith Kumar <ajith at iuac.res.in> wrote:
>> P1
>>> ---
>>>
>>> B1, B2, B3 - call +1.5V "DRAM_VCC" and +0.75V "DRAM-REF", then put 1
>>> of the capacitors connected directly to the DRAM-REF, and mark it
>>> "keep as close to DDR3 as possible", to remind yourself.  joe will
>>> know what value those need to be, but that ref voltage *must* be kept
>>
>> All the decoupling capacitors kept on one sheet for ease of handling,
>   ... but then you don't know how many you actually need, or where they
> are supposed to go!  this is a mistake
>
>>   will
>> note it down in the schematic about the critical positions. Joe is going to
>> attempt a layout. Could you give some suggestions regarding layers, the ones
>> to be dedicated for ground etc. My understanding is that there should be s
>> ground layer next to the DDR3 tracks to get the characteristic impedance
>> correct and also to give good return path. Something like:
>> L1 : tracks , L2 : ground, L3 : power, L4 : tracks, L5 : GND, L6 : tracks
>   that looks about right.
>
>> Since you already have done it,
>   i have not.  what i have done is asked SoC manufacturers to supply
> full EVB schematics.  i have then NOT ONCE MADE ONE SINGLE ALTERATION
> TO THE DDR3 LAYOUT, precisely because i know that it is beyond my
> experience and time to learn.
>
>> please make some concrete suggestions on
>> that.
>   i can't.
>
>>> A6, A7 - 24mhz XTAL is connected to RTC :)  that'll need to be to N23
>>> and N22 :)  then, if you are going to have an RTC, you *need* that
>>> 32mhz crystal - you cannot leave it off.  remember the 10M/1% resistor
>>> which needs to be put in parallel with the 32mhz XTAL.
>>
>> That was a mistake, intention is to use only the 24MHz oscillator, not the
>> 32k one. Corrected.
>   .. as in added in the 32k xtal as well?  if you do not do this, you
> *will* not have time on the device - period.
>
>>> E4, E5 - if the SY8008C is the same as the SY8008B, then you want
>>> resistors 10x that size, and you want them @ 1%.  so: R10 = 150K/1%,
>>> R11 = 100K/1%, and R13 = 442K/1% and R16 = 100K/1%.
>>
>> SY8008B or C would do 1A and 1.2A,
>   right - i see, the datasheet rev #0.9 page 3 says SY8008C does 1.5A,
> SY8008B does 1.2A
>
>> the resistors calculated as per the data
>> book. Olinuxino seems to be using 1.1K and 4.99K, I thought it is too much
>> of current wasted and used higher values. 100k & 1500k
>   150k not 1500k!!!!
>
>> will make the
>> feedback path current 4 micro amps, will it make it more prone to noise.
>> Should I change it ?
>   i have no idea.  the circuits from wits-tech use 100k and 150k and it's fine.
>
>>>
>>> also you're missing the capacitors which *must* be close to the SY8008
>>> - you want a 10uF on the IN as well as the OUT, but also on the OUT
>>> you want a 2nd much *smaller* capacitor (joe - 0.1uF?) as this catches
>>> the high frequencies.  make sure you put these as connected directly
>>> to the SY8008 because that tells you, when you come to do the layout,
>>
>> The instructions for layout will be marked in the schematic, so that is it
>> is not overlooked.
>    you're missing the point: you should *move* the capacitors onto the
> same schematic.  how the hell will you know which ones, out of a huge
> long line of 30 to 50 capacitors on page 2, are supposed to be close
> to which components??
>
>   it doesn't make any odds - you have space on P.1 for two more capacitors.
>
>>> to each and every single pin.  my recommendation here: follow the
>>> example schematic on p5 of the AXP209 datasheet.
>>
>> I did not find an English version, learned somewhat from a lower version
>> AXP202.
>   find the english translation.  look harder, and use the correct
> example.  AXP202 could be *different* from AXP209 and you would blow
> up the board as a result.
We have a machine translated version of the original Chinese spec sheet 
here
http://linux-sunxi.org/AXP209

Its not pretty but it might help.
>
>>> C7 - what's the 6-pin thing connected to DM0/DP0?  it's not marked.
>>
>> Another mistake, it is only a USB header with two shield pins. Corrected.
>   :)
>
>>>
>>> other comments:
>>>
>>> * no JTAG!  no JTAG+UART equals very very baaad :)
>>
>> Should I add a 20 pin JTAG connector or just bring  TDI0, TDO0, TMS0, TCK0
>> and RESET to a header. Please suggest.
>   i'd bring them to a header.
>
> l.
>
> _______________________________________________
> arm-netbook mailing list arm-netbook at lists.phcomp.co.uk
> http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook
> Send large attachments to arm-netbook at files.phcomp.co.uk

-- 
Neal Peacock
PengPod