Register Map
13-44
13.2.18.3
Transmit DMA Ch.n Transfer Size Counter (TXn_TSC)
The binary-encoded value from 0 to 1023, which is written by the local host into
this register, corresponds to the number of bytes or number of buffer transfers
(function of TXn_EOT), which is transmitted by the transmit DMA channel n.
When read, the register reflects the number of bytes/buffers the USB device
has left to transmit. This read mode is only provided for software debug
purposes.
For isochronous transfer, the user must verify that the set value does not
exceed the isochronous FIFO size for the endpoint. There is no
hardware mechanism to protect from this situation. If it happens, results
are unpredictable.
For bulk transfer, when TXn_EOT = 0 a set value of TXn_TSC = 0 means
1024 buffers and not 0. The counter then operates in the following way:
000, 3FF, 3FE,
…
001, 000, stop. When TXn_EOT = 1, a set value of
TXn_TSC = 0 a NULL packet is sent in response to the next IN token.
Value after local host or USB reset is low (all 10 bits).