基于NXP ARM微控制器的以太網(wǎng)吞吐量

　　本文提出了一種測量以太網(wǎng)吞吐量的方法，提供了良好的性能估計，并說明了影響性能的各種因素。

　　以太網(wǎng)是世界上應用最廣泛的局域網(wǎng)（LAN）技術。它從80年代初開始使用，并被IEEE STD 802.3所覆蓋，它指定了許多速度等級。在嵌入式系統(tǒng)中，最常用的格式是10 Mbps和100 Mbps（通常稱為10/100以太網(wǎng)）。

　　有超過20的NXP ARM MCU內(nèi)置以太網(wǎng)，涵蓋所有三代（ARM7、ARM9、ARM的Cortex-M3）。恩智浦使用基本相同的實現(xiàn)跨越三代，使設計人員可以利用他們的以太網(wǎng)功能，當系統(tǒng)進入ARM的下一代節(jié)省時間和資源。

　　本文討論了三種不同的情況下測量以太網(wǎng)吞吐量的LPC1700產(chǎn)品和細節(jié)，真正實現(xiàn)了優(yōu)化系統(tǒng)。

　　Superior implementation

　　NXP‘s Ethernet block （see Figure 1） contains a full-featured 10/100 Ethernet MAC （media access controller） which uses DMA hardware acceleration to increase performance. The MAC is fully compliant with IEEE Std 802.3 and interfaces with an off-chip Ethernet PHY （physical layer） using the Media Independent Interface （MII） or Reduced MII （RMII） protocol along with the on-chip MII Management （MIIM） serial bus.

　　The NXP Ethernet block is distinguished by the following：

　　Full Ethernet functionality — The block supports full Ethernet operation， as specified in the 802.3 standard.

　　Enhanced architecture — NXP has enhanced the architecture with several additional features including receive filtering， automatic collision back-off and frame retransmission， and power management via clock switching.

　　DMA hardware acceleration — The block has two DMA managers， one each for transmit and receive. Automatic frame transmission and reception with Scatter-Gather DMA offloads the CPU even further.