Texas Instruments OMAP36 Series, Technical Reference Manual

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McSPI Basic Programming Model
The end of the transfer (dotted line in Figure 20-37 ) is more complex and depends on the transfer type.
Table 20-17 describes the different types of end-of-transfer and the transfer types to which they are
applicable.
Table 20-17. End-of-Transfer Types
Word Count Transmit/Receive Transmit Only Receive Only
Yes See Section 20.6.3.2 , See Section 20.6.3.4 , See Section 20.6.3.5 ,
Transmit-Receive With Word Transmit-Only. Receive-Only With Word
Count. Count.
No See Section 20.6.3.3 , See Section 20.6.3.4 , See Section 20.6.3.6 ,
Transmit-Receive Without Transmit-Only. Receive-Only Without Word
Word Count. Count.
The sequence differs depending on whether word count is used (MCSPI_XFERLEVEL: WCNT is set or
not). The AEL and/or AFL values can be different, but they must be multiples of the word size in the FIFO:
1, 2, or 4 bytes, according to word length.
In these sequences, the transfer to execute has a size of N words.
When accessing the FIFO, only one word is written or read for each OCP access.
In these sequences, the number of words written or read for each write or read FIFO request is:
• write_request_size
• read_request_size
If they are not submultiples of N, the last request sizes are:
• last_write_request_size (< write_request_size)
• ast_read_request_size. (< read_request_size)
The different sequences can be merged in one process to manage transfers of several types.
The end-of-transfer sequences are described from the start of the channel.
In these sequences, some soft variables are used:
• write_count = N
• read_count = N
• last_request = FALSE
They are initialized before starting the channel.
20.6.3.2 Transmit-Receive Procedure With Word Count (WCNT ≠ 0)
Figure 20-38 shows the flow of a transfer in transmit-receive mode, with word count.
3027 SWPU177N – December 2009 – Revised November 2010 Multichannel SPI
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