TM4C1231D5PZ_15 Datasheet, PDF (934/1173 Pages) Texas Instruments – Tiva™ TM4C1231D5PZ Microcontroller

Synchronous Serial Interface (SSI)
15.3.4
■ Receive FIFO time-out
■ Receive FIFO overrun
■ End of transmission
■ Receive DMA transfer complete
■ Transmit DMA transfer complete
All of the interrupt events are ORed together before being sent to the interrupt controller, so the SSI
generates a single interrupt request to the controller regardless of the number of active interrupts.
Each of the four individual maskable interrupts can be masked by clearing the appropriate bit in the
SSI Interrupt Mask (SSIIM) register (see page 955). Setting the appropriate mask bit enables the
interrupt.
The individual outputs, along with a combined interrupt output, allow use of either a global interrupt
service routine or modular device drivers to handle interrupts. The transmit and receive dynamic
dataflow interrupts have been separated from the status interrupts so that data can be read or written
in response to the FIFO trigger levels. The status of the individual interrupt sources can be read
from the SSI Raw Interrupt Status (SSIRIS) and SSI Masked Interrupt Status (SSIMIS) registers
(see page 956 and page 958, respectively).
The receive FIFO has a time-out period that is 32 periods at the rate of SSInClk (whether or not
SSInClk is currently active) and is started when the RX FIFO goes from EMPTY to not-EMPTY. If
the RX FIFO is emptied before 32 clocks have passed, the time-out period is reset. As a result, the
ISR should clear the Receive FIFO Time-out Interrupt just after reading out the RX FIFO by writing
a 1 to the RTIC bit in the SSI Interrupt Clear (SSIICR) register. The interrupt should not be cleared
so late that the ISR returns before the interrupt is actually cleared, or the ISR may be re-activated
unnecessarily.
The End-of-Transmission (EOT) interrupt indicates that the data has been transmitted completely
and is only valid for Master mode devices/operations. This interrupt can be used to indicate when
it is safe to turn off the SSI module clock or enter sleep mode. In addition, because transmitted data
and received data complete at exactly the same time, the interrupt can also indicate that read data
is ready immediately, without waiting for the receive FIFO time-out period to complete.
Note:
In Freescale SPI mode only, a condition can be created where an EOT interrupt is generated
for every byte transferred even if the FIFO is full. If the EOT bit has been set to 0 in an
integrated slave SSI and the µDMA has been configured to transfer data from this SSI to
a Master SSI on the device using external loopback, an EOT interrupt is generated by the
SSI slave for every byte even if the FIFO is full.
Frame Formats
Each data frame is between 4 and 16 bits long depending on the size of data programmed and is
transmitted starting with the MSB. There are three basic frame types that can be selected by
programming the FRF bit in the SSICR0 register:
■ Texas Instruments synchronous serial
■ Freescale SPI
■ MICROWIRE
934
June 12, 2014
Texas Instruments-Production Data