AMD Polaris (RX 470/480/570/580) Memory Voltage
AMD Polaris cards (including the RX 470, 480, 570, and 580 are said to have a fixed memory voltage (MVDD), and it is impossible for software to change this. This, however, is not true. First, I will cite a post which describes the power delivery of these cards fairly well, and asks about software modification of the voltage. Second, I will detail how it is possible to adjust the voltage from software.
The aforementioned post is here. The specific (translated) part I wish to reference is:
Can someone confirm to me that it is not possible to modify the memory voltage (in a software way) on a reference card? According to the layout, this is not possible because the PWM 6 + 2, the +2 secondary phases are not used (the memory is controlled via a GS7256 from GStek: http://www.gstekic.com/pdf/GS7256.pdf => no i2c interface).
He is correct that the GSTek GS7256 is not software programmable. Let’s have a look at it on the reference schematics: schematic of GS7256
But, if you follow its FB input (feedback), you’ll find that there’s an I2C programmable rheostat connected to it!
Utilizing the AD5272/AD5274 digital rheostat to modify the FB (feedback) resistance, one can make the GS7256 change its output voltage. A higher resistance will raise the output voltage, a lower resistance will lower the output voltage. This is used by AMD to support different GDDR5 modules with different voltage needs.
