We are trying to save power on our iMX6ULL custom platform during lower computation periods. The idea would be to reduce DDR frequency which is a high power consumption budget.
We have tried to use low power idle DDR frequency mode (24MHz) but it is too slow for our computations, we cannot reach real time target.
We would like to run an intermediary DDR frequency (100MHz?) which seems to be named as "Audio DDR frequency" on Linux User guide (see below)
• Normal DDR frequency – Default frequency in U-Boot
• Audio DDR frequency – 50 MHz on i.MX 6Quad, i.MX 6DualLite, and i.MX 6SoloX, 100 MHz on i.MX 6SoloLite,
and 100 MHz on i.MX 7Dual
• Low power idle DDR frequency – 24 MHz
• Ultra Low power IDLE DDR frequency – 1 MHz (only on i.MX 6SoloLite)
However, iMX6ULL specific intermediary frequency does not appear on this document (L4.1.15_2.0.0-ga). Is document out of date?
When we try to force driver to pass into "Audio DDR frequency", DDR frequency stays at its default value (400MHz). Is iMX6ULL DDR controller able to run at an intermediary frequency? If yes, why isn't it available on current BSP? If not, is the limitation HW or SW?
Thank you for your help.