EZ-USB FX3 Technical Reference Manual, Document Number: 001-76074 Rev. *F 155
General Programmable Interface II (GPIF II)
7.13 GPIF II State Machine to Drive Data from Socket as Data Source
The GPIF II state machine to drive data onto the data bus is shown in Figure 7-40. The GPIF II state machine stays in the
DMAWAIT state until DMA_RDY_TH1 becomes HIGH. DMA_RDY_TH1 indicates the readiness of the DMA buffer of GPIF II
thread 1. It asserts HIGH when at least one DMA buffer of consumer socket 1 is available with data. By default, socket 1 is
mapped to thread 1.
Figure 7-40. GPIF II State Machine to Drive Data on the Data Bus
The GPIF II state machine moves to the WRITEDATA state when the DMA_RDY_TH1 flag goes HIGH. It performs the
DR_DATA action in this state. The DR_DATA action drives the data available in the DMA buffer of socket 1 onto the data bus,
one word per clock. The DR_DATA action settings are shown in Figure 7-41.
Figure 7-41. DR_DATA Action Setting
The GPIF II state machine returns to the DMAWAIT state when the DMA_RDY_TH1 flag goes low. This happens when DMA
buffer switching occurs for the created DMA channel or when all the allocated DMA buffers are empty and waiting to get data
from the USB side.
When GPIF II tries to read data from the DMA buffer after it is emptied, then a PIB underrun error is flagged for the
corresponding thread. The bit fields of the PIB error indicator register let you know if a PIB error is flagged.
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