Ac'97 Link Controller; Specific Features; Figure 358. Ac'97 Audio Frame - ST STM32F423 Reference Manual

Serial audio interface (SAI)
30.11

AC'97 link controller

The SAI is able to work as an AC'97 link controller. In this protocol:
•
The slot number and the slot size are fixed.
• The frame synchronization signal is perfectly defined and has a fixed shape.
To select this protocol, set bit PRTCFG[1:0] in the SAI_xCR1 register to 10. When AC'97
mode is selected the data sizes that can be used are 16-bit or 20-bit only, else SAI behavior
is not guaranteed.
•
Bits NBSLOT[3:0] and SLOTSZ[1:0] are consequently ignored.
•
The number of slots is fixed at 13 slots. The first one is 16 bits wide and all the others
are 20 bits wide (data slots).
•
Bit FBOFF[5:0] in the SAI_xSLOTR register is ignored
•
The SAI_xFRCR register is ignored.
The FS signal from the block defined as asynchronous is configured automatically as an
output, since the AC'97 controller link drives the FS signal whatever the master or slave
configuration.
Figure 358
Note: In AC'97 protocol, bit 2 of the tag is reserved (always 0), so whatever the value written in the
SAI FIFO, bit 2 of the TAG is forced to 0 level.
For more details about TAG representation, please refer to the AC'97 protocol standard.
One SAI can be used to target an AC'97 point-to-point communication.
In receiver mode, the SAI acting as an AC'97 link controller will require no FIFO request and
so no data storage in the FIFO when the codec ready bit in the slot 0 is decoded low. If bit
CNRDYIE is enabled in the SAI_xIM register, flag CNRDY will be set in the SAI_xSR
register and an interrupt is generated. This flag is dedicated to the AC'97 protocol.
30.12

Specific features

The SAI has some specific functions which can be useful depending on the audio protocol
selected. These functions are accessible through specific bits in the SAI_xCR2 register.
1000/1324
presents an AC'97 audio frame structure.

Figure 358. AC'97 audio frame

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