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MibSPI Operation Modes
18
2.8
Multi-buffer RAM
The size of the multi-buffer RAM depends on the implementation. It is
comprised of 0 to 128 buffers, where 0 buffers represents the special case of
no multi-buffer RAM. Each entry in the multi-buffer RAM consists of four parts:
a 16-bit transmit field, a 16-bit receive field, a 16-bit control field and a 16-bit
status field.The multi-buffer RAM can be partitioned into multiple transfer
groups with a variable number of buffers each. In Figure 11 three examples
are shown for a multi-buffer RAM with 64 buffers and four transfer groups.
The first example shows two transfer groups used to partition the 64 buffers.
In the second example all buffers are partitioned four times and in the third
example only the first 32 buffers are utilized.
Figure 11.
Example: Different Modes for a Multi-buffer RAM of 64 Buffers
Each of the transfer groups can be configured individually. For each of the
transfer groups, a trigger event and a trigger source can be chosen. A trigger
event can be, for example, a rising edge or a permanent low level at a
selectable trigger source. A last trigger type is “always”, which means either
continuous mode or single mode depending on the ONESHOT control bit. Up
to 15 trigger sources are available, which can be utilized by each transfer
group. One of these trigger sources is called tick counter. This tick counter is
implemented in the MibSPI and generates periodic trigger events. Other
trigger sources can be MibSPI external signals coming from another
peripheral module like the High-End Timer (HET) or a general-purpose input
pin (GPIO).
An interrupt can be generated upon finishing a group transfer or when an
ongoing group transfer is suspended due to “suspend to wait” state of one of
the buffers inside the transfer group. This suspend interrupt enables the host
to quickly provide new transmit data or to quickly consume received data from
the suspended buffer.
dual transfer group
quadruple transfer group
transfer group 0:
18 buffers
PSTART0=0
32 buffers dual transfer group
transfer group 1:
46 buffers
PSTART1=18
PSTART2=0
Buffer 0
Buffer 1
...
Buffer 17
Buffer 18
Buffer 19
...
Buffer 62
Buffer 63
transfer group 0:
10 buffers
PSTART0=0
transfer group 1:
28 buffers
PSTART1=10
transfer group 2:
1 buffer
PSTART2=38
transfer group 3:
25 buffers
PSTART3=39
LPEND=0
Buffer 0
Buffer 1
...
Buffer 9
Buffer 10
Buffer 11
...
Buffer 37
Buffer 38
Buffer 39
Buffer 40
Buffer 63
transfer group 0:
18 buffers
PSTART0=0
PEND=18-1
transfer group 1:
14 buffers
PSTART1=18
PSTART2=32
LPEND=32
Buffers 32 to 63
remain unused
Buffer 0
Buffer 1
...
Buffer 17
Buffer 18
Buffer 19
...
Buffer 31
Buffer 32
Buffer 63
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