ESP32: EOI - high-speed UART driver

[jmattsson]

The UART driver provided by Espressif in the IDF is full featured, and integrated into the IDF VFS and all those things. It is also big and complex (three levels of buffering - aaah!). And the UART ISR sits in flash. The latter turns out to be a show stopper if you're using high baud rates like 1Mbit and are wanting to write to flash at the same time. While the flash erase/write is taking place, the UART interrupt is blocked (since the ISR resides in flash, and the flash is inaccessible during an erase/write) and this leads to lost bytes.

At $work we had to work around this, so I have written a replacement, high-performance UART driver specifically for NodeMCU. Its ISR sits in RAM so it does not get blocked by flash operations, and it also provides full configurability of the RAM FIFOs (queues) used, so they can be dimensioned according to the particular project requirements, per UART. We're for example using an 8K receive queue and 512byte send queue on one of the UARTs, and 2k/8byte on the second.

Is there any interest in me PR'ing this UART driver here? Comments for and against below, please :)

It's a Kconfig option whether to use it or the standard IDF driver, and it defaults to off (i.e. use IDF driver). The downside to it is that it uglifies the platform.c a bit, as there are effectively two implementations there depending on which driver is used. I should also mention that the console UART is not affected by the driver change, as it already has its own driver.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[NicolSpies]

@jmattsson, @galjonsfigur, maybe this should not be closed in light of #3104.

[jmattsson]

If there's actual interest then sure. I'd let this one languish since there were no comments here.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.