I refer to Technical Reference Manual SPRUH22G, revised January 2015. I have several questions:
1) In section 23.3.7 it states "For example, if the 1/4 option is selected for the receive FIFO, the UART generates a receive interrupt after 4 data bytes are received."
I interpret this as when the 4th character is completely received (for 1/4 FILL level option), the interrupt will be generated, whether or not ANY OTHER CHARACTERS ARE EVER RECEIVED.
However, in section 23.6.9 it states "The interrupts are generated based on a transition through a level rather than being based on the level. That is, the interrupts are generated when the fill level progresses through the trigger level. For example, if the receive trigger level is set to the half-way mark, the interrupt is triggered as the module is receiving the 9th character."
I interpret this as ONLY when the 5th character is beginning to be (completely?) received (again, for 1/4 FILL level option), the interrupt will be generated.
These two statements seem in conflict with each other. Either the interrupt occurs after the 4th character is received OR only as the module is receiving (or has completely received?) the 5th character. Please clarify.
2) In Table 23-10 the RXIFLSEL value of 0x0 is shown as meaning RX FIFO >= 1/2 full. However value 0x2 is ALSO showing as meaning RX FIFO >= 1/2 full. To be consistent it seems that 0x0 should mean RX FIFO >= 1/8 full. I believe therefore that this is merely a typo in the documentation. Please confirm.
3) In the same table the TXIFLSEL values are shown to indicate TX FIFO <= xx empty. This is confusing.
A TX FIFO trends from MORE FULL towards LESS FULL as data is serialized and transmitted.
Alternatively, a TX FIFO trends from LESS EMPTY towards MORE EMPTY as data is serialized and transmitted.
I think the table is incorrect. Examples of what I think:
0x1 TX FIFO >= 3/4 empty - CORRECT (interrupt as transition towards MORE EMPTY)
0x1 TX FIFO <= 3/4 full - ALSO CORRECT (interrupt as transition towards LESS FULL)
0x1 TX FIFO <= 3/4 empty - INCORRECT
Please review and comment.
Thank you in advance.
Steve C.
