The reasons for this problem has a lot of,
First from the simple principle: 1. I am using adc capture: let the adc is set in the clock frequency scan access level unceasingly, can obtain duty ratio and frequency, etc., 2 then is to make the dma data to the dac output: first of all need to set up a dma transmission mode (peripherals (p) to the memory (m), p to p, m to m, m to p) choose the m to p here, because I had written the memory (an array), then only need to send the data to dac (peripherals), set up after the m to p this mode, how to make the data to the dac the peripherals rather than other peripherals? This will have to find the manual about data flow datastream channel or channels (depending on which model you are using is), I am using f407zg, for example, here the dma data stream is 5 channel 7 corresponding dac1, find, just can make the data flow and channel even successful connection, the following is my tone for a few days didn't find the problem, the dma can need to make, namely dma_cmd, so after how long a mind's eye, each used a new things, to see if it need not to need the command can make, no reaction this problem, also have to check whether the functions are the command,