Hi,
On Thu, Jul 30, 2015 at 5:45 PM, Mikhail Yakshin <greycat@xxxxxxxxxxxxx> wrote:
> Hi,
>
> I've been analyzing various boards based on Allwinner A20 CPU and
> X-Powers AXP209 PMU (to make a proper configuration for our board,
> Whitebox Labs Watermelon).
>
> There are some things very common and some things pretty different on
> various boards.
>
> Namely, there's agreement on that DCDC2 and DCDC3 and used for CPU
> voltages (VDD-CPU and (VDD-SYS=VDD-INT)+VDD-DLL respectively) on all
> boards I've analyzed (Olimex boards, Cubieboard / Cubietruck, BananaPi,
> PCDuino, Watermelon, etc) and probably it should be kept this way.
>
> However, what puzzles me the most so far is LDO1 regulator. According to
> [AXP209 datasheet, p. 13, p. 23][1] and all the boards I've
> investigated, it's used exclusively for powering VDD-RTC input of A20
> CPU that supports internal CPU's RTC. LDO1 gets very special status in
> AXP209 - basically, it's as close to "always on" (even on backup
> battery) as possible the purpose of timekeeping.
>
> According to the same spec, LDO1 allows 2 distinct voltage choices: 1.3V
> and 3.3V. However, according to the [A20 datasheet][2], VDD-RTC (pin K8)
> has absolute minimum and maximum voltage ratings of 3.0V. I'm not sure
> how is it supposed to work together, given that X-Powers AXP209 and
> Allwinner A20 is basically produced by different branches the same
> company and are meant to be totally compatible.
Get an updated datasheet. Mine (v1.5 20150510) recommends VDD-RTC to
be 1.2 V ~ 1.4 V, and nominally at 1.3 V.
Also, my AXP209 datasheet (v1.0 Chinese) says LDO1SET grounded means
LDO1 is set to 1.3 V.
> What's even more weird, is that all configurations I've encountered so
> far (i.e. FEX configurations for 3.4 sunxi kernel and DTS for modern
> mainline kernels) use hard locked 1.3V setting for LDO1. For example,
> kernel 3.4:
>
> /sys/devices/platform/sunxi-i2c.0/i2c-0/0-0034/axp20-regulator.21/regulator/regulator.1/
> name axp20_ldo1
> microvolts 1300000
> min_microvolts 1300000
> max_microvolts 1300000
>
> and similar construction in mainline DTSes:
>
> vdd_rtc: ldo1 {
> regulator-min-microvolt = <1300000>;
> regulator-max-microvolt = <1300000>;
> regulator-always-on;
> };
>
> or in axp209.dtsi:
>
> reg_ldo1: ldo1 {
> /* LDO1 is a fixed output regulator */
> regulator-always-on;
> regulator-min-microvolt = <1300000>;
> regulator-max-microvolt = <1300000>;
> regulator-name = "ldo1";
> };
>
> If we'll take a look at default power-on setup for AXP209 in the
> datasheet (page 24), we'll see that it's determined by LDO1SET pin. If
> it's connected to GND, then LDO1 will start with 1.3V, if it's connected
> to VINT, then it would be 3.3V.
>
> I've analyzed all the schematics I found in public:
>
> * Older Olimex schematics (Lime rev C, Lime rev D, Lime2 rev B) state
> that LDO1 line is "3V3/30mA". LDO1SET is grounded.
> * Newer Olimex schematics (Lime2 rev C) call that "1V3/30mA". LDO1SET is
> grounded.
> * All Bananapi and Cubieboard schematics look very similar and seem to
> be originating from the same source (reference Allwinner design?) and do
> not hint any voltages. LDO1SET is grounded.
>
> Can someone explain to me how does it work / supposed to work?
See above.
ChenYu
> [1]: http://linux-sunxi.org/images/8/89/AXP209_Datasheet_v1.0en.pdf
> [2]:
> https://github.com/OLIMEX/OLINUXINO/raw/master/HARDWARE/A20-PDFs/A20%20Datasheet%20v1.0%2020130227.pdf
>
> --
> WBR, Mikhail Yakshin
>
>
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