Default frequency of extperiph1

[user41388]

Hello,

According to the Sensor Software Driver Programming - Device Properties, the maximum frequency of extperiph1 is 24 MHz.

Well, I took a Jetson, flashed it with the Nvidia SDK, boot, and then run the command:

cat /sys/kernel/debug/bpmp/debug/clk/extperiph1/rate

The output is 37090909, as in, ~37.1 MHz. If I run:

cat /sys/kernel/debug/bpmp/debug/clk/extperiph1/max_rate

The output is also 37090909.

Based on this, I’m led to believe that 37.1 MHz is the default value for extperiph1.

I’m aware that this topic is partly related to Maximum output frequency of CAM0_MCLK and Master clock question on CSI interface, but they do not answer the questions:

1. Why is the default value 37.1 MHz?
2. Can the default be changed?
3. Why is extperiph1 being set (by default) to a value larger than the documented maximum of 24 MHz?

[JerryChang]

hello user41388,

this is calculated by following… extperiph1 = pll_p (408MHz) / div(11)
it’s due to particular camera requires higher frequencies, and, it’s only extperiph1 with higher frequencies.

[user41388]

Would be great if this information can be updated in the manual: Sensor Software Driver Programming - Device Properties.

Probably best to write that the maximum rate can be checked with cat /sys/kernel/debug/bpmp/debug/clk/extperiph1/max_rate

[JerryChang]

hello user41388,

FYI,
doc update has complete to revise the maximum frequency for extperiph1 to 37.09MHz in [Sensor Software Driver Programming].
it’ll also mention others (i.e. extperiph2/extperiph3/extperiph4) are limited to 24Mhz.