Visible to Intel only — GUID: lro1402201740154
Ixiasoft
Visible to Intel only — GUID: lro1402201740154
Ixiasoft
31.4.6. Control Field
The control field is available for both the standard and extended descriptor formats. This field can be programmed to configure parked descriptors, error handling, and interrupt masks. The interrupt masks are programmed into the descriptor so that interrupt enables are unique for each transfer.
Bit | Sub-Field Name | Definition |
---|---|---|
31 | Go |
Commits all the descriptor information into the descriptor FIFO. As the host writes different fields in the descriptor, FIFO byte enables are asserted to transfer the write data to appropriate byte locations in the FIFO. However, the data written is not committed until the go bit has been written. As a result, ensure that the go bit is the last bit written for each descriptor. Writing '1' to the go bit commits the entire descriptor into the descriptor FIFO(s). |
30:26 | <reserved> | |
25 | Wait for write responses | When set, on completion of the DMA transfer, the host is only notified when all the outstanding writes have been responded. Those outstanding writes include writes transfer initiated by previous descriptor. This field is valid only when Enable Write Response parameter is set. Enabling this bit resulted in longer time for write response host to move into the next descriptor. Therefore, it is recommended to set this field on the last descriptor of the transfer. |
24 | Early done enable | Hides the latency between read descriptors. When the read host is set, it does not wait for pending reads to return before requesting another descriptor. Typically this bit is set for all descriptors except the last one. This bit is most effective for hiding high read latency. For example, it reads from SDRAM, PCIe, and SRIO. |
23:16 | Transmit Error / Error IRQ Enable | For for Avalon® -MM to Avalon® -ST transfers, this field is used to specify a transmit error. This field is commonly used for transmitting error information downstream to streaming components, such as an Ethernet MAC. In this mode, these control bits control the error bits on the streaming output of the read host. For Avalon® -ST to Avalon® -MM transfers, this field is used as an error interrupt mask. As errors arrive at the write host streaming sink port, they are held persistently. When the transfer completes, if any error bits were set at any time during the transfer and the error interrupt mask bits are set, then the host receives an interrupt. In this mode, these control bits are used as an error encountered interrupt enable. |
15 | Early Termination IRQ Enable | Signals an interrupt to the host when a Avalon® -ST to Avalon® -MM transfer completes early. For example, if you set this bit and set the length field to 1MB for Avalon® -ST to Avalon® -MM transfers, this interrupt asserts when more than 1MB of data arrives to the write host without the end of packet being seen. |
14 | Transfer Complete IRQ Enable | Signals an interrupt to the host when a transfer completes. In the case of Avalon® -MM to Avalon® -ST transfers, this interrupt is based on the read host completing a transfer. In the case of Avalon® -ST to Avalon® -MM or Avalon® -MM to Avalon® -MM transfers, this interrupt is based on the write host completing a transfer. |
13 | <reserved> | |
12 | End on EOP | End on end of packet allows the write host to continuously transfer data during Avalon® -ST to Avalon® -MM transfers without knowing how much data is arriving ahead of time. This bit is commonly set for packet-based traffic such as Ethernet. |
11 | Park Writes | When set, the dispatcher continues to reissue the same descriptor to the write host when no other descriptors are buffered. |
10 | Park Reads | When set, the dispatcher continues to reissue the same descriptor to the read host when no other descriptors are buffered. This is commonly used for video frame buffering. |
9 | Generate EOP | Emits an end of packet on last beat of a Avalon® -MM to Avlaon-ST transfer |
8 | Generate SOP | Emits a start of packet on the first beat of a Avalon® -MM to Avalon® -ST transfer |
7:0 | Transmit Channel | Emits a channel number during Avalon® -MM to Avalon® -ST transfers |