Hi,
On 19-09-16 18:07, TsvetanUsunov wrote:
Hi,
We make our final touch of A64-OLinuXino PCB and there we add option eMMC Flash
to work on dual voltages 1.8V and 3.3V.
The eMMC is connected to AXP803 pin.34 GPIO1/LDO. The problem is that when A64
boots and AXP803 is not initialized it outputs default 0.8V then after
initialization driver takes care to drive it 1.8V or 3.3V.
This makes impossible to boot from eMMC which is not good. We now think for
solution which to drive eMMC at 3.3V initially when AXP803 output is below 1.8V
but this adds unnecessary hardware complexity.
For hardware point of view it will be much more simplier if dedigated A64 GPIO
is used and initially is pulled down and after AXP803 is initialized is pulled
up.
Ok, so what your suggesting is:
axp803-ldo-io1 -\
[mux]---> mmc-supply
Fixed-3.3v ------/ |
|
|mux-control
A64 gpio out--------/
Note the above ascii-art requires a fixed-width font.
With a pull-down (or pull-up) to fix the mux in a certain position when the
gpio is in tri-state ?
As long as we pin the axp803-ldo-io1 at 1.8v then the Linux regulator
framework should be able to deal with, and in u-boot we can just
keep things at 3.3v.
How would you suggest us to implement it? Will this additional GPIO create
troubles in eMMC driver philosophy?
For the Linux mmc driver the mmc-supply is abstracted as a regulator,
and the regulator framework should be able to deal with any setup
you can come up with.
For the SDMMC we are still hesitating what to do as we don't know if the card
which will be inserted will support low voltage and higher speeds at all.
As long as you default to 3.3v then the kernel's sd subsystem can
dynamically switch voltage (through e.g. the gpio) if the card
advertises it supports low voltage. Note that you're planning
the first board to implement this that I know off, so the sunxi-mmc
kernel driver will need some work to support voltage switching,
but in the mean time things should work fine at 3.3v.
Also eMMC Flash and SDMMC card should be driven by separate voltages, as they
may work in any combinations.
Ack, right, as said both cards should come up with 3.3v and then
a new voltage will be negotiated before switching, so this definitely
needs to be per card.
This means we need another AXP803 LDO and another GPIO for the SDMMC card.
Right.
Regards,
Hans
By the way the current eMMC from Micron we use has 11MB Write speed no matter
what is the voltage and this is written in the datasheet, so maybe we should
switch and add this dual voltage to the SD MMC where someone could use SD MMC
card supporting higher clocks?
I would love to hear your opinion.
Tsvetan
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