ST STM32F40 Series Reference Manual page 965

Ethernet (ETH): media access control (MAC) with DMA controller
●
RDES1: Receive descriptor Word1
31 30 29 28 27 26 25
RBS2
rw rw rw rw rw rw rw
Bit 31 DIC: Disable interrupt on completion
When set, this bit prevents setting the Status register's RS bit (CSR5[6]) for the received frame
ending in the buffer indicated by this descriptor. This, in turn, disables the assertion of the interrupt to
Host due to RS for that frame.
Bits 30:29 Reserved, must be kept at reset value.
Bits 28:16 RBS2: Receive buffer 2 size
These bits indicate the second data buffer size, in bytes. The buffer size must be a multiple of 4, 8,
or 16, depending on the bus widths (32, 64 or 128, respectively), even if the value of RDES3
(buffer2 address pointer) is not aligned to bus width. If the buffer size is not an appropriate multiple
of 4, 8 or 16, the resulting behavior is undefined. This field is not valid if RDES1 [14] is set.
Bit 15 RER: Receive end of ring
When set, this bit indicates that the descriptor list reached its final descriptor. The DMA returns to
the base address of the list, creating a descriptor ring.
Bit 14 RCH: Second address chained
When set, this bit indicates that the second address in the descriptor is the next descriptor address
rather than the second buffer address. When this bit is set, RBS2 (RDES1[28:16]) is a "don't
care" value. RDES1[15] takes precedence over RDES1[14].
Bit 13 Reserved, must be kept at reset value.
Bits 12:0 RBS1: Receive buffer 1 size
Indicates the first data buffer size in bytes. The buffer size must be a multiple of 4, 8 or 16,
depending upon the bus widths (32, 64 or 128), even if the value of RDES2 (buffer1 address
pointer) is not aligned. When the buffer size is not a multiple of 4, 8 or 16, the resulting behavior is
undefined. If this field is 0, the DMA ignores this buffer and uses Buffer 2 or next descriptor
depending on the value of RCH (bit 14).
965/1422
24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
RBS2
rw rw rw rw rw rw rw rw rw rw rw
Doc ID 018909 Rev 4
9 8 7 6
RBS
rw rw rw rw rw rw rw rw rw rw rw rw rw
RM0090
5 4 3 2 1 0