https://github.com/anholt/linux/blob/e50da9745215df2260169ff0685423dbf43ee2d3/drivers/soc/bcm/bcm2835-pm.c#L132-L137

this file has code that can enable various power domains withint he rpi

PM_PROC example (arm cpu cores)

start by clearing the ARMRSTN flag
wait 15 usec
set POWUP bit (enables power to that block)
wait for POWOK status
set ISPOW (some kind of electrical isolation)
set MEMREP (memory repair?)
wait for MRDONE (mem repair done)
set ISFUNC (functional isolation)


https://www.raspberrypi.org/documentation/raspbian/applications/vcgencmd.md

code found behind `vcgencmd measure_volts`
sdram phy  sdram_p: A2W_SMPS_LDO1 >> 18
sdram io   sdram_i: A2W_SMPS_LDO0 >> 10
sdram core sdram_c: A2W_SMPS_LDO0 >> 15

those 3 registers are all signed 5 bit ints

&0x1f to select just the reg of interest
&0x10 to detect negative
|0xffff_ffe0 to sign extend

to convert to volts, (X * 25 + 1200) * 0.001

each tick of the 5bit int represents 0.025volts of offset, relative to a baseline of 1.2v, max range: 0.8v<->1.575v

core: A2W_SMPS_A_VOLTS
another 5bit int, sign extend, 0.025 volt increments, 1.2v baseline, but then offset by something in GP
then convert backwards into a 5bit int, and further translate into the -16<->+8 range, and convert back to voltage??

https://github.com/raspberrypi/linux/issues/932
PM_RSTS docs




pi3
power applied but reset held
4.73v (crappy cable)
110mA

network booted, VPU at 500mhz but held in sleep
4.78v
124mA

netboot, VPU 250mhz, held in sleep
4.79v
116mA

vpu now 125mhz
4.81v
112mA

100mhz
4.81v
112mA


10mhz
4.82v
111mA

https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=292538
> 1.2V is the defailt voltage when idle.
> It increases when in turbo mode by an amount that varies with silicon. (And you are forcing turbo mode always).




pi0
arm_clock pllb    divisor   core_v
100mhz    2.4ghz  /24       1.2
200mhz    2.4ghz  /12       1.35
300mhz    2.4ghz  /8        1.35
400mhz    3.2ghz  /8        1.35
500mhz    2ghz    /4        1.35
600mhz    2.4ghz  /4        1.35
700mhz    2.8ghz  /4        1.35

700mhz    2.8ghz  /4        1.2
800mhz    3.2ghz  /4        1.35
900mhz    1.8ghz  /2        1.35
1ghz      2ghz    /2        1.35