HD6417705 Datasheet, PDF (514/739 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

18.7 DMA Transfer
18.7.1 Overview
DMA transfer can be performed for endpoints 1 and 2 in this module. Note that word or longword
data cannot be transferred.
When endpoint 1 holds at least one byte of valid receive data, a DMA request for endpoint 1 is
generated. When endpoint 2 holds no valid data, a DMA request for endpoint 2 is generated.
If the DMA transfer is enabled by setting the EP1DMAE bit to 1 in the DMA transfer setting
register, zero-length data reception at endpoint 1 is ignored. When the DMA transfer is enabled,
the RDFN bit for EP1 and PKTE bit for EP2 do not need to be set to 1 in TRG (note that the
PKTE bit must be set to 1 when the transfer data is less than the maximum number of bytes).
When all the data received at EP1 is read, the FIFO automatically enters the EMPTY state. When
the maximum number of bytes (64 bytes) are written to the EP2 FIFO, the FIFO automatically
enters the FULL state, and the data in the FIFO can be transmitted (see figures 18.15 and 18.16).
18.7.2 DMA Transfer for Endpoint 1
When the data received at EP1 is transferred by the DMAC, the USB function module
automatically performs the same processing as writing 1 to the RDFN bit in TRG if the currently
selected FIFO becomes empty. Accordingly, in DMA transfer, do not write 1 to the RDFN bit in
TRG. If the user writes 1 to the RDFN bit in DMA transfer, correct operation cannot be
guaranteed.
Figure 18.15 shows an example of receiving 150 bytes of data from the host. In this case, internal
processing which is the same as writing 1 to the RDFN bit in TRG is automatically performed
three times. This internal processing is performed when the currently selected data FIFO becomes
empty. Accordingly, this processing is automatically performed both when 64-byte data is sent
and when data less than 64 bytes is sent.
64 bytes
64 bytes
22 bytes
RDFN
(Automatically
performed)
RDFN
RDFN
(Automatically (Automatically
performed) performed)
Figure 18.15 RDFN Bit Operation for EP1
Rev. 2.00, 09/03, page 468 of 690