STMicroelectronics STM32F405 Reference Manual page 930

Serial audio interface (SAI)
An interrupt is generated if FREQIE bit is enabled in the SAI_xIM register. This depends on:
•
FIFO threshold setting (FLTH bits in SAI_CR2)
•
Communication direction transmitter or receiver (see
transmitter mode
Interrupt generation in transmitter mode
The interrupt generation depends on the FIFO configuration in transmitter mode:
• When the FIFO threshold bits in SAI_XCR2 register are configured as FIFO empty
(FTH[2:0] set to 000b), an interrupt is generated (FREQ bit set by hardware to 1 in
SAI_XSR register) if no data are available in SAI_xDR register (FLTH[2:0] bits in SAI_xSR
is less than 001b). This Interrupt (FREQ bit in SAI_XSR register) is cleared by hardware
when the FIFO became not empty (FLTH[2:0] bits in SAI_xSR are different from 000b) i.e
one or more data are stored in the FIFO.
• When the FIFO threshold bits in SAI_XCR2 register are configured as FIFO quarter full
(FTH[2:0] set to 001b), an interrupt is generated (FREQ bit set by hardware to 1 in
SAI_XSR register) if less than a quarter of the FIFO contains data (FLTH[2:0] bits in
SAI_xSR are less than 010b). This Interrupt (FREQ bit in SAI_XSR register) is cleared by
hardware when at least a quarter of the FIFO contains data (FLTH[2:0] bits in SAI_xSR
are higher or equal to 010b).
• When the FIFO threshold bits in SAI_XCR2 register are configured as FIFO half full
(FTH[2:0] set to 010b), an interrupt is generated (FREQ bit set by hardware to 1 in
SAI_XSR register) if less than half of the FIFO contains data (FLTH[2:0] bits in SAI_xSR
are less than 011b). This Interrupt (FREQ bit in SAI_XSR register) is cleared by hardware
when at least half of the FIFO contains data (FLTH[2:0] bits in SAI_xSR are higher or
equal to 011b).
• When the FIFO threshold bits in SAI_XCR2 register are configured as FIFO three quarter
(FTH[2:0] set to 011b), an interrupt is generated (FREQ bit is set by hardware to 1 in
SAI_XSR register) if less than three quarters of the FIFO contain data (FLTH[2:0] bits in
SAI_xSR are less than 100b). This Interrupt (FREQ bit in SAI_XSR register) is cleared by
hardware when at least three quarters of the FIFO contain data (FLTH[2:0] bits in
SAI_xSR are higher or equal to 100b).
• When the FIFO threshold bits in SAI_XCR2 register are configured as FIFO full (FTH[2:0]
set to 100b), an interrupt is generated (FREQ bit is set by hardware to 1 in SAI_XSR
register) if the FIFO is not full (FLTH[2:0] bits in SAI_xSR is less than 101b). This Interrupt
(FREQ bit in SAI_XSR register) is cleared by hardware when the FIFO is full (FLTH[2:0]
bits in SAI_xSR is equal to 101b value).
Interrupt generation in reception mode
The interrupt generation depends on the FIFO configuration in reception mode:
• When the FIFO threshold bits in SAI_XCR2 register are configured as FIFO empty
(FTH[2:0] set to 000b), an interrupt is generated (FREQ bit is set by hardware to 1 in
SAI_XSR register) if at least one data is available in SAI_xDR register(FLTH[2:0] bits in
SAI_xSR is higher or equal to 001b). This Interrupt (FREQ bit in SAI_XSR register) is
cleared by hardware when the FIFO became empty (FLTH[2:0] bits in SAI_xSR is equal
to 000b) i.e no data is stored in FIFO.
• When the FIFO threshold bits in SAI_XCR2 register are configured as FIFO quarter fully
(FTH[2:0] set to 001b), an interrupt is generated (FREQ bit is set by hardware to 1 in
SAI_XSR register) if at less one quarter of the FIFO data locations are available
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and Section : Interrupt generation in reception
DocID018909 Rev 11
Section : Interrupt generation in
mode)
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