UART on ATmega8

[modm-io]

UART on ATmega8

[salkinium]

 $ lbuild -r repo.lb -D :target=atmega8 discover -t :platform
Module(modm:platform)   Platform HAL
├── Module(modm:platform:1-wire.bitbang)   Software 1-Wire
├── Module(modm:platform:adc)   Analog-to-Digital Converter (ADC)
├── Module(modm:platform:can.common)   CAN Common
├── Module(modm:platform:clock)   System Clock
│   ╰── NumericOption(f_cpu) = REQUIRED in [1 ... 32000000]   CPU clock frequency
├── Module(modm:platform:core)   AVR Core
│   ├── EnumerationOption(ram_block_length) = 16 in [2, 4, 8, 16, 32, 64]
│   ╰── NumericOption(ram_length) = 1024 in [64 .. 1024 .. 32768]
├── Module(modm:platform:gpio)   General Purpose I/O (GPIO)
├── Module(modm:platform:gpio.common)   GPIO Common
├── Module(modm:platform:i2c)   Inter-Integrated Circuit (I²C)
├── Module(modm:platform:i2c.bitbang)   Software Inter-Integrated Circuit (I²C)
├── Module(modm:platform:spi)   Serial Peripheral Interface (SPI)
│   ╰── BooleanOption(busywait) = False in [True, False]
╰── Module(modm:platform:spi.bitbang)   Software Serial Peripheral Interface (SPI)

Hm… why isn't there a UART module?

[salkinium]

There is no "instance" in the driver in modm-devices:

    driver = device.get_driver("usart")
    if "instance" in driver:
        for instance in listify(driver["instance"]):
            module.add_submodule(Instance(int(instance)))
    else:
        return False

=> From here

<driver name="usart" type="avr"/>

=> From here

[salkinium]

Looking at the ATmega8 datasheet, modm-devices is correct, the instance is called just USART, not USART0. So the driver needs to be adapted to work with a None or "" (empty string) instance.

[salkinium]

The SPI driver does something similar already, by building in modm:platform:spi directly instead of a submodule. I'm not sure why I didn't port this from xpcc the same way: https://github.com/modm-io/modm/blob/develop/src/modm/platform/spi/at90_tiny_mega/module.lb#L79-L92