19718: drivers/dht: busy wait reimplementation r=benpicco a=hugueslarrive
### Contribution description
In PR #19674, I also provided quick and dirty fixes to restore functionality on esp8266 and enable operation on AVR. While reviewing PR #18591, it became apparent to me that this driver needed a refresh, particularly its migration to ztimer.
The cause of the malfunction on esp8266 was that since the default switch to ztimer as the backend for xtimer, XTIMER_BACKOFF was no longer taken into account. Therefore, the correction I provided in PR #19674 simply made explicit what was previously done implicitly with xtimer and now needs to be done explicitly with ztimer (spinning instead of sleeping).
Moreover, it was unnecessarily complex to measure the pulse duration in a busy-wait implementation, which required 2 calls to ztimer_now() and 32-bit operations expensive on 8-bit architecture. Instead, it is sufficient to read the state of the bus at the threshold moment.
Finally, in practice, it is possible to reduce the read interval (down to less than 0.5s for DHT22) by "harassing" the DHT with start signals until it responds.
This re-implementation brings the following improvements:
- Many backports from `@maribu's` IRQ based implementation (#18591):
- Use of ztimer
- Use of errno.h
- Use of a dht_data structure to pass arguments, to facilitate integration
- Adaptation of the bit parsing technique to parse bits into the data array
- Reintroduction of DHT11/DHT22 differentiation.
- Separation of `dht_read()` steps into functions for better readability and the ability to share certain functions among different implementations
- Sensor presence check in `dht_init()`
- ~~Automatic adjustment to a minimum data hold time~~
- Default input mode changed to open drain (a pull-up resistor should be placed close to the output if necessary but not close to the input)
- AVR support without platform-specific handling by avoiding ztimer_spin() and using the overflow of an 8-bit variable as a pre-timeout to minimize time-consuming ztimer_now() calls
Regarding the changes in the start signal sequence and the removal of the `_reset()` function:
~~In the previous implementation, there was an unnecessary spike at the beginning of the signal sequence, corresponding to START_HIGH_TIME. This spike has been removed in the re-implementation, as it is unnecessary. Instead, the MCU now simply pulls the signal low for START_LOW_TIME and then releases the bus, which is sufficient for initiating communication with the DHT sensor.~~ Actually, it is necessary to raise the bus level; otherwise, the _wait_for_level() called immediately after to check the response of the DHT may read the port before the signal level is raised, resulting in a false positive.
Additionally, the previous implementation had an issue where the MCU switched back to output mode and went high immediately after reading the 40 bits of data. However, the DHT sensor was still transmitting 2 or 3 additional bytes of '0' at that point, causing a conflict. This issue has been resolved in the re-implementation:
~~Regarding the optimization for AVR, I have performed measurements of `_wait_for_level()` until timeout (85 loops):~~
~~- on esp8266-esp-12x: 264 µs, which is 3.11 µs per loop~~
~~- on nucleo-f303k8: 319 µs, which is 3.75 µs per loop~~
~~- on arduino-nano: 3608 µs, which is 42.45 µs per loop~~
~~Duration measurements on the Arduino Nano:~~
19737: dist/tools/openocd: start debug-server in background and wait r=benpicco a=fabian18
19746: buildsystem: Always expose CPU_RAM_BASE & SIZE flags r=benpicco a=Teufelchen1
### Contribution description
Hello 🐧
This moves the definition of `CPU_RAM_BASE/SIZE` from being only available in certain situation to be always available.
Reason for change is to simplify common code in the cpu folder.
In cooperation with `@benpicco`
### Testing procedure
Passing CI
### Issues/PRs references
First usage will be in the PMP driver. Although there is more code in RIOT that could be refactored to use these defines instead of hacks / hardcoded values.
Co-authored-by: Hugues Larrive <hlarrive@pm.me>
Co-authored-by: Fabian Hüßler <fabian.huessler@ml-pa.com>
Co-authored-by: Teufelchen1 <bennet.blischke@outlook.com>
561e19303d