I want to let the AM335x enter more low power consumption when it is in idle mode as following method:
1. In Linux, OS schedule a idle task to let CPU enter WFI mode.
2. I've modified the code of the idle task, before CPU enter WFI mode, I'll put the PLLs of Core and MPU enter bypass mode.
kernel code:
local_irq_disable();
do_gettimeofday(&before);
cpu_do_idle();
do_gettimeofday(&after);
local_irq_enable();
The function "cpu_do_idle" shall let CPU enter "WFI" mode.
modified kernel code:
local_irq_disable();
do_gettimeofday(&before);
core_mpu_pll_bypass();
cpu_do_idle();
core_mpu_pll_restore();
do_gettimeofday(&after);
local_irq_enable();
The function "core_mpu_pll_bypass" shall let the PLLs of core and MPU enter bypass mode, the function "core_mpu_pll_restore" shall let the PLLs of core and MPU resume.
3. Added the PLLs of Core and MPU enter bypass mode, the power consumption of idle state is less than WFI only mode.
4. In my opinion, idle task is only handle the CPU idle. When CPU idle, DMA maybe works. If I put the PLL of core to bypass mode when cpu idle, it could reduce the DMA speed if there is a DMA transfer but cpu is idle. So I need to figure out the DMA status(it works or not) to bypass the PLL of core or not. If DMA works, the idle task shall not bypass the PLL of core.
Does anyone know how to judge whether the DMA controller is in use(DMA works or not)? It seems that there is no register related.
