SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The TDM-mode transmission settings are relevant for I2S-protocol and protocols using more than 2 TDM-slots.
XSSZ should always be programmed to match the slot size of the serial stream.
Note that, TDM word size is not directly programmed into the McASP, but rather is used to determine the rotation needed in the XROT field.
The Table 24-331 show the XRVRS and XROT fields for each serial format and for both integer and Q31 fractional internal representations.
The Table 24-331 assumes that all slot size (SLOT in Table 24-331) and word size (WORD in Table 24-331) options are multiples of 4, since the transmit rotate right unit only supports rotation by multiples of 4. However, the bit mask/pad unit does allow for any number of significant digits. For example, a Q31 number may have 19 significant digits (word) and be transmitted in a 24-bit slot; this would be formatted as a word size of 20 bits and a slot size of 24 bits. However, it is possible to set the bit mask unit to only pass the 19 most-significant digits (program the mask value to FFFF E000h). The digits that are not significant can be set to a selected pad value, which can be any one of the significant digits, a fixed value of 0, or a fixed value of 1.
The transmit bit mask/pad unit operates on data as an initial step of the transmit format unit, and the data is aligned in the same representation as it is written to the transmitter by the MPU or DSP (typically Q31 or integer).
Bit Stream Order | Bit Stream Alignment | Internal Numeric Representation | MCASP_TXFMT bits | |
---|---|---|---|---|
XROT(1) | XRVRS | |||
MSB first(2) | Left aligned | Q31 fraction | 0 | 1 |
MSB first | Right aligned | Q31 fraction | SLOT - WORD | 1 |
LSB first | Left aligned | Q31 fraction | 32 - WORD | 0 |
LSB first | Right aligned | Q31 fraction | 32 - SLOT | 0 |
MSB first(2) | Left aligned | Integer | WORD | 1 |
MSB first | Right aligned | Integer | SLOT | 1 |
LSB first | Left aligned | Integer | 0 | 0 |
LSB first | Right aligned | Integer | (32 - (SLOT - WORD)) % 32 | 0 |