ISO TXDMA[0,1, 2]
start routine
EP number
−−>
TXDMA_CFG.
Assign ISO endpoint number
to DMA channel n.
Application-specific
action to initialize the
main system DMA
controller
LH DMA write access
must point to
TXDCHn.TXDATn in
response to DMA
channel n request.
End of ISO TXDMA
[0,1, 2]
start routine
Start DMA transfer:
TXDMAn._TSC = FTZ,
TXDMAn.TXn_EOT = 1,
TXDMAn.TXn_START = 1.
If no interrupt is signaled to
the LH (except SOF if
enabled), the Device DMA
sends a new request to the LH
DMA controller every frame.
EOT bit is don’t care for ISO
endpoints.
TXDMAn_EP
USB Device Controller
1650
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Universal Serial Bus (USB)
29.3.27.8 Isochronous IN (USB HOST -> CPU) DMA Transactions
For ISO endpoints, the transfer size counter (TXDMAn.TXn_TSC) corresponds to the number of bytes to
transmit. The programmed size must not exceed the programmed buffer size of the endpoint. Otherwise,
the result is unpredictable (see
).
A request to the CPU main DMA controller is generated when the endpoint buffer is empty initially after
the START bit is set, and then after each SOF (every 1 ms). The request is removed when the number of
bytes written in the buffer matches the TXDMAn.TXn_TSC value.
During ISO transfers to a DMA operated IN endpoint, a request to the CPU system DMA controller is
generated every 1-ms frame when an isochronous data packet is received with no error. There is no
special interrupt associated with the DMA transfer.
No interrupt is signaled to the CPU during DMA operation to ISO IN endpoints.
Figure 29-92. ISO TX DMA Start Routine