If the _IRQ_L2CAP_RECV handler does the actual consumption of the incoming
data (i.e. via l2cap_recvinto), rather than setting a flag for
non-scheduler-context to handle it later, then two things can happen:
- It can starve the VM (i.e. the scheduled task never terminates). This is
because calling l2cap_recvinto will empty the rx buffer, which will grant
more credits to the channel (an HCI command), meaning more data can
arrive. This means that the loop in hal_uart.c that keeps reading HCI
data from the uart and executing NimBLE events as they are created will
not terminate, preventing other VM code from running.
- There's no flow control (i.e. data will arrive too quickly). The channel
shouldn't be given credits until after we return from scheduler context.
It's preferable that no work is done in scheduler/IRQ context. But to
prevent this being a problem this commit changes l2cap_recvinto so that if
it is called in IRQ context, and the Python handler empties the rx buffer,
then don't grant credits until the Python handler is complete.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
47d02b3104