Issue: When the memory-mapped flash region is accessed while the flash
read mode is disabled (fctrl.en flag is clear), the SPI flash controller
generates an invalid response on the D channel.
This may cause the TileLink bus to deadlock.
Workaround: Software should avoid accessing the memory-mapped flash
region when the SPI controller is not in the flash read mode.
Issue: Configuring the frame length to certain values causes incorrect
operation.
Symptoms: Certain frame lengths result in the master sending one extra
clock pulse. The slave device may then become desynchronized.
Workaround: The following frame lengths are supported and can be used.
Do not use other frame lengths.
* Serial mode: 0, 2, 4, 6, 8
* Dual mode: 0, 1, 3, 5, 7, 8
* Quad mode: 0, 1, 2, 3, 5, 6, 7, 8
Issue: The output enable signal for DQ[3] is not driven properly.
Symptoms: Output data from master to slave is not properly transmitted
in quad mode. Data received from the slave is unaffected.
Workaround: When interfacing with SPI flash devices, do not use the
"Quad Input/Output Fast Read" command (opcode 0xEB) while in the
Extended SPI protocol. Do not use the Native Quad SPI protocol.
Previously we had to do weird things to make non-homogenous
lists of items (e.g. PWM Peripherals where ncmp were different from one to
the other) into a vector. But now Chisel supports a Record type,
and we use the HomogenousBag utility to do this more naturally.
This also deletes all the cruft which was introduced to get
around the limitation which doesn't exist anymore.
