When running on armv6, set alignment checking to modulo-4 mode rather
than modulo-8, because clang emits ldrd and strd instructions for
addresses that are only 4-byte aligned.
When running on armv6, set alignment checking to modulo-4 mode rather
than modulo-8, because clang emits ldrd and strd instructions for
addresses that are only 4-byte aligned
Accommodate uart devices with large FIFOs (or DMA buffers which amount
to the same thing) by allocating the uart(4) rx buffer based on the
device's rxfifosz rather than using a hard-coded size of 384 bytes.

The  historical 384 byte size is 3 times the largest hard-coded fifo
size in the tree, so use that ratio as a guide and allocate the buffer
as three times rxfifosz, but never smaller than the historical size.