[question] Voltage calculation

[karolherbst]

In the vbios of Kepler gpus is a P table (We cal it Voltage Map Table) with all the voltage entries for each clock state and the performance levels.

Each of those entries contain some min/max voltage and 6 coefficients which are used to calculate the final voltage for the given clock state or performance level.

in the end, depending on the 0th byte, the final voltage is calculated (on my GPU by):

0: c0 * 0.1 + c1 * 168 + c2 * 28
1: c0 * 0.06 + c1 * 100 + c2 * 15.3 * T + c3 * 100 + c4 * 41 + c5 * 0.065 * T^2

now my questions:

1. Are those factors in any way hardware specific or are the same factors used for every gpu?
2. If those factors are hw specific, where could we find those? (I would suspect them inside PFUSE)
3. what would be the exact coefficients

[karolherbst]

well I spend more time and got closer to the calculation:

S: speedo
T: temperature

mode0:
c0 / 10
c1 * S / 10
c2 * S^2 / 10^5

mode1:
c0 * 5^6 >> 18
c1 * S * 5^6 >> 18
c2 * T * 5^6 >> 10
c3 * S * T * 5^6 >> 18
c4 * S^2 * 5^6 >> 30
c5 * T^2 * 5^6 >> 18

mode2: min
mode3: (min+max)/2

I am pretty sure this is right, so I just need a confirmation

[Gnurou]

Hi Karol,

The P-table actually contains many sub-tables, which Nouveau selects using the following code:

    if (!bit_entry(bios, 'P', &bit_P)) { <- this extracts P table
            if (bit_P.version == 2)
                    cstep = nvbios_rd16(bios, bit_P.offset + 0x34); <- this extracts sub-table (here, 0x34 offset gives voltage-frequency table)

Can you clarify which bit_P.offset values you are using, so we know which sub-table is referred to and check the coefficients properly?

[ghost]

He's referring to the CVB table (+0x20).

[karolherbst]

what is CVB? But yeah, it is the +0x20 table.

[karolherbst]

are there any updates on this one so far?

[Gnurou]

Pinged again, trying to get an answer...

[karolherbst]

thanks a lot