The main purpose of this new COM implementation is that it is
much simpler, and requires less code space. This takes a bit
of the pressure off of the CC bootloader which was right at
the limit of available code space in the bootloader partition.
This is not intended to ever be used by the application.
This driver also formalizes the assumptions in the bootloader's
usage of the COM layer. All messages are assumed to arrive
in atomic chunks from the HID layer.
The PIOS_COM_ReceiveBufferUsed() function call is no longer
necessary since the same semantics can be achieved using calls
to PIOS_COM_ReceiveBuffer().
The small bootloaders (CC and PipX) are out of flash space
so their stopwatch implementation has been swapped out for
one based on the DELAY clock that takes about 500 bytes less
of code space.
Identical functionality is preserved.
This allows the spektrum and sbus receiver drivers to bind
directly to the usart layer using a properly exported API
rather than overriding the interrupt handler.
Bytes are now pushed directly from the usart layer into the
com layer without any buffering. The com layer performs all
of the buffering.
A further benefit from this approach is that we can put all
blocking/non-blocking behaviour into the COM layer and not
in the underlying drivers.
Misc related changes:
- Remove obsolete .handler field from irq configs
- Adapt all users of PIOS_COM_* functions to new API
- Fixup callers of PIOS_USB_HID_Init()
Now that every bootloader build has a board info blob,
make all fw and bl images use it.
The following MACROS are removed:
BOARD_TYPE, BOARD_REVISION, BOOTLOADER_VERSION,
START_OF_USER_CODE, HW_TYPE
These values are now ONLY available from the bootloader
flash via the pios_board_info_blob symbol. These values
must not be #defined or otherwise hard-coded into the
firmware in any way. The bootloader flash is the only
valid source for this information.
NOTE: To ensure that we have an upgrade path from an
old bootloader (without board_info_blob) to a
new bootloader (with board_info_blob), it is
essential that the bu_* targets do not depend
on (or validate) the board_info_blob being present
in the bootloader flash.
