lsr

Reserved bits [31:8] - Read Only

Receiver FIFO Error bit.
This bit is only relevant when FIFO_MODE != NONE AND FIFO's are enabled (FCR[0]
set to one). This is used to indicate if there is at least one parity error, framing
error, or break indication in the FIFO. That is:
0 = no error in RX FIFO
1 = error in RX FIFO
This bit is cleared when the LSR is read and the character with the error is at the
top of the receiver FIFO and there are no subsequent errors in the FIFO.

Transmitter Empty bit.
If in FIFO mode (FIFO_MODE != NONE) and FIFO's enabled (FCR[0] set to one), this
bit is set whenever the Transmitter Shift Register and the FIFO are both empty.
If in the non-FIFO mode or FIFO's are disabled, this bit is set whenever the
Transmitter Holding Register and the Transmitter Shift Register are both empty.

Transmit Holding Register Empty bit.
If THRE_MODE_USER == Disabled or THRE mode is disabled (IER[7] set to zero) and
regardless of FIFO's being implemented/enabled or not, this bit indicates that
the THR or TX FIFO is empty. This bit is set whenever data is transferred from
the THR or TX FIFO to the transmitter shift register and no new data has been
written to the THR or TX FIFO. This also causes a THRE Interrupt to occur, if the
THRE Interrupt is enabled.
If THRE_MODE_USER == Enabled AND FIFO_MODE != NONE and both modes are active
(IER[7] set to one and FCR[0] set to one respectively), the functionality is switched
to indicate the transmitter FIFO is full, and no longer controls THRE interrupts,
which are then controlled by the FCR[5:4] threshold setting. Programmable THRE
interrupt mode operation is described in detail in section 5.7 on page 52.

Break Interrupt bit.
This is used to indicate the detection of a break sequence on the serial input data.
If in UART mode  it is set whenever the serial input, sin, is held in a logic '0'
state for longer than the sum of start time + data bits + parity + stop bits.
If in infrared mode  it is set whenever the serial input, sir_in, is continuously
pulsed to logic '0' for longer than the sum of start time + data bits + parity + stop
bits.
A break condition on serial input causes one and only one character, consisting of
all zeros, to be received by the UART. In the FIFO mode, the character associated
with the break condition is carried through the FIFO and is revealed when the
character is at the top of the FIFO. Reading the LSR clears the BI bit. In the
non-FIFO mode, the BI indication occurs immediately and persists until the LSR is
read.

Framing Error bit.
This is used to indicate the occurrence of a framing error in the receiver. A framing
error occurs when the receiver does not detect a valid STOP bit in the received data.
In the FIFO mode, since the framing error is associated with a character received, it
is revealed when the character with the framing error is at the top of the FIFO. When
a framing error occurs the UART will try resynchronize. It does this by assuming that
the error was due to the start bit of the next character and then continues receiving
the other bit i.e. data, and/or parity and stop.
It should be noted that the Framing Error (FE) bit (LSR[3]) will be set if a break
interrupt has occurred, as indicated by Break Interrupt (BI) bit (LSR[4]).
0 = no framing error
1 = framing error
Reading the LSR clears the FE bit.

Parity Error bit.
This is used to indicate the occurrence of a parity error in the receiver if the
Parity Enable (PEN) bit (LCR[3]) is set. In the FIFO mode, since the parity error is
associated with a character received, it is revealed when the character with the parity
error arrives at the top of the FIFO.
It should be noted that the Parity Error (PE) bit (LSR[2]) will be set if a break
interrupt has occurred, as indicated by Break Interrupt (BI) bit (LSR[4]).
0 = no parity error
1 = parity error
Reading the LSR clears the PE bit.

Overrun error bit.
This is used to indicate the occurrence of an overrun error. This occurs if a new data
character was received before the previous data was read. In the non-FIFO mode, the OE
bit is set when a new character arrives in the receiver before the previous character
was read from the RBR. When this happens, the data in the RBR is overwritten. In the
FIFO mode, an overrun error occurs when the FIFO is full and a new character arrives at
the receiver. The data in the FIFO is retained and the data in the receive shift register
is lost.
0 = no overrun error
1 = overrun error
Reading the LSR clears the OE bit.

Data Ready bit.
This is used to indicate that the receiver contains at least one character in the
RBR or the receiver FIFO.
0 = no data ready
1 = data ready
This bit is cleared when the RBR is read in the non-FIFO mode, or when the receiver
FIFO is empty, in the FIFO mode.