The use of DMA in serial data transmission systems

W artykule przedstawiono projekt układu wykorzystującego w transmisji danych kontroler DMA. Głównym zadaniem kontrolera jest odciążenie jednostki centralnej użytego mikrokontrolera przez bezpośredni dostęp do jego pamięci. Badanie transmisji przeprowadzono za pomocą analizatora stanów logicznych LOGIC8 wraz z dedykowanym do niego oprogramowaniem producenta. Analiza otrzymanych wyników potwierdza, iż uzyskana szybkość transmisji danych przy zastosowaniu kontrolera DMA jest o 16% większa niż w przypadku klasycznej obsługi procesu komunikacji z zastosowaniem procesora.In this paper authors proved that DMA controller have positive effect on the serial transmission process. Firstly, was presented a scheme with principles of the device using DMA controller. The stream of data sent from sensor can use one of four modes, it means: without DMA, with DMA on sensor side, with DMA on PC side and with DMA on both sides. The main device was assembled with following modules: LSM9DS0 sensor as a data generator, STM32F4 ARM microcontroller for data transmssion, USART-USB converter and PC computer as a data reader. The main module is the ARM microcontroller which controls whole process. Additionally, authors present used transmission interfaces working between the modules. In research 18 kB of data is send from the sensor to the computer and time of data transmission is measured. There are different structures of data frame in range of 3000 buffers containing 6b of data to 6 buffers containing 3000b. The speed for the SPI and UART amounted to 5.25 Mb/s. The times for the case: 1018 executed delay loops are presented in Table 2 and are given in milliseconds. In result transmission fully controlled by DMA is 16,6% faster than CPU controlled one (pulling mode) and 5,2% faster than CPU utilizing interrupts. Transmission controlled by CPU utilizing interrupts is 12,1% faster than CPU controlled one (in pulling mode). The fastest transmission achieved 60% of theoretical transmission speed