SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP
RSSZ should always be programmed to match the slot size of the serial stream.
Note that the word size is not directly programmed into the MCASP, but rather is used to determine the rotation needed in the RROT field.
Table 12-6 shows the RRVRS and RROT fields for each serial format and for both integer and Q31 fractional internal representations.
Bit Stream Order | Bit Stream Alignment | Internal Numeric Representation | MCASP_RFMT bits | |
---|---|---|---|---|
RROT(1) | RRVRS | |||
MSB first(2) | Left aligned | Q31 fraction | SLOT | 1 |
MSB first | Right aligned | Q31 fraction | WORD | 1 |
LSB first | Left aligned | Q31 fraction | (32 - (SLOT - WORD)) % 32 | 0 |
LSB first | Right aligned | Q31 fraction | 0 | 0 |
MSB first(2) | Left aligned | Integer | SLOT - WORD | 1 |
MSB first | Right aligned | Integer | 0 | 1 |
LSB first | Left aligned | Integer | 32 - SLOT | 0 |
LSB first | Right aligned | Integer | 32 - WORD | 0 |
The Table 12-6 assumes that all slot size and word size options are multiples of 4; since the receive 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 received 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 receive bit mask/pad unit operates on data as the final step of the receive format unit (see Figure 12-17), and the data is aligned in the same representation as it is read from the receiver (typically Q31 or integer).