ST16C554 works in FIFO mode, receives and transmits data by (interrupt) mode with a 16 byte hardware transmitbuffer, that will also greatly cut down the load on the CPU.
Tcp_receivespace -in addition to controlling the amount of buffer space to be consumed by receive buffers, AIX also USES this value to determine the size to make its transmit window.
The SPU (a) queues a DMA PUT to transmit the contents of buffer #1 and then (b) queues a DMA GETB to execute after the PUT to refill the buffer with the next portion of data from main memory.
SPU (a) 对 DMA PUT 进行排队来传输一号缓冲区的内容，然后 (b) 对 DMA GETB 进行排队，从而在 PUT 之后 用主内存中的下一部分数据重新填充这个缓冲区。