use input port as counter

[pasau]

Hi, i've encountered something in the usb reference design that requires some sort of clarification. First, there is the output port from a certain PLL that is input to give a clock reference.

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/* Clock master clock-block from master-clock port */
    configure_clock_src(clk_audio_mclk, p_mclk_in);

Then this clock is used to clock an in port

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asm("ldw %0, dp[clk_audio_mclk]":"=r"(x));
asm("setclk res[%0], %1"::"r"(p_for_mclk_count), "r"(x));

But the port p_for_mclk_count, is not attached to anything, in fact it is declared as P16B, from which only the bit 15 is available on a pin on the u8-64-fb96. Im assuming they use the buffered port as a reference timer, since the port is never input and all the application ever does is getting the port timestamp. but why use a port for this purpose?

[segher]

What else would you use? The alternative is to count clock
edges "by hand", not such a hot idea.

[Ross]

Annoyingly with the current architecture you can only get clock ticks out of a port (getts instruction) not a clock block...

The port isn't used for anything apart from getting the clock count out of the clock block. Any unused port could be used.

[pasau]

i get it thanks. In short it serves as a timer which can be driven by any clockblock, and not just the system clock?