I had a look to the firmware.
In order to cope with strict timings of 802.15.4, in its implementation,
Freescale sets the modem in streaming mode, otherwise there will be not enough
time for sending an ack (macAckWaitDuration is 54 symbol periods = 864us).
In streaming mode, while rx is in progress, the modem interrupts the CPU once
every 64us (2 octects received) and the CPU reads the 2 octects via SPI. Once
rx is done CPU is ready to send an ack immediately.
In your implementation, instead, the received packet is buffered and has to be
entirely read from modem RAM. Then it must be forwarded over the UART. The
kernel might have to check if buffers for indirect transmission are pending to
set the bit in the ack. Then the ack must be transmitted back over the SCI and
finally to the modem. Is this really feasible?
Thanks
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