Timer1，3，4 DMA trigger sources：是否支持 capture mode，就是输入信号上升/下降沿触发时，是否可以用DMA把计数值传送到内存？
硬件手册 swru191d.pdf 中的说明有前后不一致的情况。请TI 的工程师确认一下。
#############第98页 Table 8-1. DMA Trigger Sources：
2 T1_CH0 Timer 1 Timer 1, compare, channel 0
3 T1_CH1 Timer 1 Timer 1, compare, channel 1
4 T1_CH2 Timer 1 Timer 1, compare, channel 2
5 T2_EVENT1 Timer 2 Timer 2, event pulse 1
6 T2_EVENT2 Timer 2 Timer 2, event pulse 2
7 T3_CH0 Timer 3 Timer 3, compare, channel 0
8 T3_CH1 Timer 3 Timer 3, compare, channel 1
9 T4_CH0 Timer 4 Timer 4, compare, channel 0
10 T4_CH1 Timer 4 Timer 4, compare, channel 1
所有都是compare，没有capture。
#############第113页 9.11 Timer 1 DMA Triggers
There are three DMA triggers associated with Timer 1. These are DMA triggers T1_CH0, T1_CH1, and
T1_CH2, which are generated on timer compare events as follows:
• T1_CH0 – Channel 0 compare
• T1_CH1 – Channel 1 compare
• T1_CH2 – Channel 2 compare
所有都是compare，没有capture。
#############第123页 10.7 Timer 3 and Timer 4 DMA Triggers
Two DMA triggers are associated with Timer 3, and two DMA triggers are associated with Timer 4.
• T3_CH0: Timer 3 channel 0 capture/compare
• T3_CH1: Timer 3 channel 1 capture/compare
• T4_CH0: Timer 4 channel 0 capture/compare
• T4_CH0: Timer 4 channel 1 capture/compare
所有都是既有compare，也有capture。