QDMA Descriptor Credit Input Ports - 4.0 English

QDMA Subsystem for PCI Express Product Guide (PG302)

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Table 1. QDMA Descriptor Credit Input Port Descriptions
Port Name I/O Description
dsc_crdt_in_vld I Valid. When asserted the user must be presenting valid data on the bus and maintain the bus values until both valid and ready are asserted on the same cycle.
dsc_crdt_in_rdy O Ready. Assertion of this signal indicates the DMA is ready to accept data from this bus.
dsc_crdt_in_dir I Indicates whether credits are for H2C or C2H descriptor ring.

0: H2C

1: C2H

dsc_crdt_in_fence I

If the fence bit is set, the credits are not coalesced, and the queue is guaranteed to generate a descriptor fetch before subsequent credit updates are processed. The fence bit should only be set for a queue that is enabled, and has both descriptors and credits available, otherwise a hang condition might occur.

dsc_crdt_in_qid [10:0] I The QID associated with the descriptor ring for the credits are being added.
dsc_crdt_in_crdt [15:0] I The number of descriptor credits that the user application is giving to QDMA Subsystem for PCIe to fetch descriptors from the host.