在以SD卡為圖像存儲器件的圖像協處理器中，基帶芯片和SD卡控制器在速度上的差異經常會導致數據傳輸錯誤。為解決此問題，設計了一種可適應多種時序情況的DMA控制器。該DMA控制器的狀態機，一方面對基帶芯片和SD卡控制器的操作請求進行仲裁，在響應基帶芯片請求的同時，適當推遲SD卡控制器的請求；另一方面對DMA讀寫的數據進行計數，并以此判斷SD卡的一次多塊讀或多塊寫操作是否完成；最后對基帶芯片和SD卡控制器的速度做出判斷，必要時暫停速度較快一方的操作。實際工作表明，該DMA控制器能夠在基帶芯片和SD卡控制器之間正確傳輸數據并使讀寫SD卡的速度達到210 kB/s。

Abstract:

?In the image coprocessor which used SD card as memory，there is a speed difference between baseband and SD card controller. The difference will result some errors in data transmission. To solve the problem，the DMA controller adapted for several timing cases was designed. On the one hand，after arbitrating operation requests from baseband and SD card controller，the DMA controller responded to a request of baseband and delayded another. On the other hand，by counting the number of data in a DMA operation，the controller determined whether a read or write operation of multiple block should done or not. In the end，the DMA controller estimated the speed of baseband and SD card controller and broke the operations of the faster one. In practice，the DMA controller transfers data correctly between baseband and SD card controller and enhances the speed of read or write operation of SD card to 210kB/s.