esp32: add support for uart pin inversions

[jeremyherbert]

The ESP32 supports inversion of UART TX/RX/RTS/CTS. This adds support for inversions as optional kwargs:

u = UART(1, baudrate=115200, parity=1, bits=8, rx=27, tx=32, rx_invert=True, tx_invert=True)

[dpgeorge]

Thanks for the contribution. This adds a lot of new arguments and it might be better to simplify it by combining them all together into a single invert argument. This can then be set via a bit mask, eg:

u = UART(1, 9600, invert=UART.INV_TX | UART.INV_RX)

[jeremyherbert]

Ok, I will do that this evening.

[jeremyherbert]

I’ve been thinking about this, if the bitmask approach is used, should the str printout show the individual bits? Or show the calculated mask (ie 0x3)? Or nothing?

[dpgeorge]

if the bitmask approach is used, should the str printout show the individual bits

Usually (well, sometimes) the output of str would be some text that can be reevaluated to produce the same object. Printing the calculated mask would work for this. So would the individual bits like invert=INV_TX|INV_RX. The latter is how stm32's UART prints the flow control.

[jeremyherbert]

Ok, you can now invert all four lines via a mask. Here is how it looks:

MicroPython v1.11-418-g96faf5a3b-dirty on 2019-10-11; ESP32 module with ESP32
Type "help()" for more information.
>>> from machine import UART
>>> u = UART(1, 115200)
>>> u
UART(1, baudrate=115201, bits=8, parity=None, stop=1, tx=10, rx=9, rts=-1, cts=-1, txbuf=256, rxbuf=256, timeout=0, timeout_char=1)
>>> u = UART(1, 115200, invert=UART.INVERSE_TX|UART.INVERSE_RX)
>>> u
UART(1, baudrate=115201, bits=8, parity=None, stop=1, tx=10, rx=9, rts=-1, cts=-1, txbuf=256, rxbuf=256, timeout=0, timeout_char=1, invert=INVERSE_TX|INVERSE_RX)
>>> u = UART(1, 115200, invert=7)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid inversion mask
>>> 

Only issue is that you can't use it as-is to construct a new object as the mask bits are under the UART class, ie "UART.INVERSE_TX" rather than just "INVERSE_TX".

[robert-hh]

Using an integer for invert=xx should work. You just have to pick the right values.
UART_INVERSE_RX = 2**19 + 1
UART_INVERSE_TX = 2**19 + 8
UART_INVERSE_CTS = 2**19 + 2
UART_INVERSE_RTS = 2**19 + 16
I implemented that reecntly for anothe MP branch, and shifted the values forth & back for convenience.

[jeremyherbert]

It does work :) I just added that as an example of the error, 7 is not a valid mask. If you were to put in a correct integer mask it would go through fine

[dpgeorge]

Thanks for updating, merged in 7a7ee16