+ * The instantiator should set the blockSize, which represents the maximum
+ * number of bytes the underlying SPI stack will transmit or receive in a
+ * single interrupt service. Increasing the block size decreases SPI
+ * communications time at the expense of reducing system responsiveness to
+ * other events.
+ *
+ * The blockSize is best set by considering the maximum time the SPI stack
+ * should be able to delay other events. A rule of thumb formula would be:
+ *
+ * block_time = block_size / (spi_bitclock/8)
+ *
+ * For example, using a 500KHZ SPI bitclock, a block size of 64 bytes
+ * equates to a block time of 1 ms. Note that this calculation is rough
+ * because it does not take into account ISR overhead and other factors.
+ *
+ * The implementation will use a default blockSize if set to 0 here.
+ *
+ * @author R. Steve McKown <rsmckown@gmail.com>