Hi!
What do you mean by latency?
pin_a0=low_usec_delay(10)pin_a0=highTXREG=255
The time which the serial start bit is delayed more than 1 Tcy I would call
latency. The time that follows then is the time required for transmission,
which is at least 10/baudrate (8 data plus 1 start plus 1 stop bits).
The first byte written to TXREG is going right through to the Transmit Shift
Register (TSR), while the second byte stays in the (user accessible) TXREG,
going automatically to TSR once that is free. If you want to send a third byte,
the library has to wait for TXREG to be free, or data would be overwritten and
lost.
So yes, if you're sending three bytes, the library will have to delay data,
either by blocking the program (serial_hardware) or by caching the data in a
software buffer (serial_hw_int_cts).
I haven't seen a library induced latency before. I presume the 80uS you've seen
are more related to the number of three bytes and the baudrate than to the
32MHz the controller is running on.
Greets,Kiste
Am Sonntag, 17. Oktober 2021, 12:12:49 MESZ hat vsurducan
<[email protected]> Folgendes geschrieben:
Hi all, just an info.
Serial_hw_write library seems to add a quite large latency for the real
signals. For example the following instructions:
serial_hw_write (address)
serial_hw_write (dataH)
serial_hw_write (dataL)
;_usec_delay ( 100 )
compiled on a 32MHz clock microcontroller are adding a measurable latency of
about 80uS which seems a bit weird.
If those instructions are chained in a critical time loop, a delay after those
three compiler instructions is mandatory, without it, the communication may
freeze. Actually this delay includes the communication latency. I've used a
logic analyzer to understand that behavior.best wishes,
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