i.MX6 Trace Clock

bcody — Fri, 23 Jul 2021 00:36:17 GMT

I've been having some difficulty dialing in the trace clock on the i.MX 6 DL. I believe it is attached to the ahb_clk_root (pg 782 of the RM) but there is no talk of a divider. Given the 792 MHz core clock (and two cores!) you need a fairly substantial clock to get data out without losing it to fifo full errors, especially since there's not guarantee of a 32-bit wide trace bus. However it seems like something has divided the clock to be half the frequency of the ahb. The trace clock is half-rate, so with the default ahb clock rate (132 MHz), the half-frequency trace clock (66 MHz) is sampling at 132 MHz. This is not nearly enough to keep up with the processor.

So two questions:
1) Is it possible to increase the trace clock rate to match the AHB, or is there any independent control?

2) Is it possible to suspend the cores when trace falls behind to reduce or eliminate data loss?

Thank you.

Re: i.MX6 Trace Clock

igorpadykov — Sat, 31 Jul 2021 00:12:36 GMT

Hi Brian

unfortunately answers are "no" for both questions. Trace clocks are derived directly from

the AHB clock. There is no ability to change the trace clock frequencies other than changing

the AHB clock frequency, which will have multiple side effects in the system. So essentially,
no you cannot change the Trace clock frequency.

Usually it is recommended to use the ETB. In this mode you don't need to
configure ETM, IO pins and you don't need even special trace hardware: standard
JTAG signals are used. The trace is collected via JTAG. The disadvantage in this mode
is that the trace is not collected in real time and the maximal size of trace buffer is 4K.

Best regards
igor

i.MX Processorsのトピックi.MX6 Trace Clock

i.MX6 Trace Clock

Re: i.MX6 Trace Clock