[RP2040] Allow any GPIO pin for RS485 direction pin #6330
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As I mentioned in issue adafruit#6310 while investigating that the Teensy port did not support RS485_dir pin on normal GPIO pins, I found that it was not implemented either as well on some other ports. So was curious to implement it for RP2040 using same approach as I did for the MIMXRT in the Pull Request adafruit#6328 That is I setup the specified pin as a normal GPIO pin in output mode and then when you do a write operation it sets the GPIO pin logically high, and when the write completes I set it logically low. Note: knowing when I can set it low can be tricky, as you need to make sure the full output has completed otherwise the data will be corrupted. I am using: uart_tx_wait_blocking(self->uart); Which looks like it is supposed to wait until the busy status is no longer set, which the Reference manual mentioned, but this is leaving the line logically set longer than I would like. however I have tried running it with my hacked up version of the Python Robotis DynamixelSDK and was able to talk to some AX servos. I did have to change the library slightly for the RP2040, as the library was erroring out when you did something like uart.read(5) and it timed out without receiving anything. The RP2040 returned None whereas I think the Teensy returned an empty set, which is what it looks like the PySerial original code expects. Not sure if anyone is interested in this, but thought i would put it out as PR and see.
dhalbert
reviewed
May 4, 2022
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I am concerned that this software impl of RS485 might fail occasionally due to timing issues, as I mentioned here for i.MX: #6328 (review).
The discussion I have found about RS485 on RP2040 discusses using PIO instead of the regular UART, because that way the direction pin timing can be guaranteed.
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Added doc caveat in #6328. |
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As I mentioned in issue #6310 while investigating that the Teensy port
did not support RS485_dir pin on normal GPIO pins, I found that it
was not implemented either as well on some other ports.
So was curious to implement it for RP2040 using same approach as I did
for the MIMXRT in the Pull Request #6328
That is I setup the specified pin as a normal GPIO pin in output mode
and then when you do a write operation it sets the GPIO pin logically
high, and when the write completes I set it logically low.
Note: knowing when I can set it low can be tricky, as you need to make
sure the full output has completed otherwise the data will be corrupted.
I am using: uart_tx_wait_blocking(self->uart);
Which looks like it is supposed to wait until the busy status is no
longer set, which the Reference manual mentioned, but this is leaving
the line logically set longer than I would like.
however I have tried running it with my hacked up version of the
Python Robotis DynamixelSDK and was able to talk to some AX servos.
I did have to change the library slightly for the RP2040, as the
library was erroring out when you did something like uart.read(5)
and it timed out without receiving anything. The RP2040 returned
None whereas I think the Teensy returned an empty set, which is what
it looks like the PySerial original code expects.
Not sure if anyone is interested in this, but thought i would
put it out as PR and see.