This will initialize those structs with zero in all fields not set
and all fields set will only be change once to the final value not
wasting CPU time zeroing it.
This will guarantee that no non-unitialized structs will have
a trash value on from_external causing it to be sent to the
MAVLink channel without need it.
The previous approach was checking system id and component id but it
will not work in 100% of cases as external devices can send MAVLink
message with the right system id but with broadcast component id.
Define the default I2C buss frequncies that are backward compatible
with the existing code. While allowing it the defaults to be overridden
by a board config.
Based on the legacy STM32 code, the I2C buss numbering starts at 1.
The bus frequency is stored in a 0 based array. If px4_i2cbus_initialize
returns a valid device, then the _bus-1 will act as the index to the
busses frequency.
A board may define BOARD_NUMBER_I2C_BUSES - the number of I2C busses
it supports* and BOARD_I2C_BUS_CLOCK_INIT to initalize the bus
clocks for a given busses.
BOARD_NUMBER_I2C_BUSES - the number of busses including the *highest
number bus. If the board has 2 I2C
busses I2C1 and I2C3 BOARD_NUMBER_I2C_BUSES
would be set to 3
BOARD_I2C_BUS_CLOCK_INIT - Initalization for the bus frequencies
by bus. A call init, with a frequency
less then the value used for the
Initalization will result in the device
not starting becuase the buss runs too
fast for it.
PX4_NUMBER_I2C_BUSES number of busses that the HW can support
not all of them my be usesd. I.E. The STM32F427 has 3 I2C
busses but only I2C1 and I2C3 are used.
* For some reason cppcheck complains with `fp != nullptr` but accepts truthiness
of handle by itself.
* Note that the expressions are equivalent according to the C++ standard ("A
prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member
type can be converted to a prvalue of type bool. A zero value, null pointer
value, or null member pointer value is converted to false; any other value is
converted to true. A prvalue of type std::nullptr_t can be converted to a
prvalue of type bool; the resulting value is false.")
Daniel Agar