Functional Description
Channel teardown may be commanded on any channel at any time. The host is informed of the teardown
completion by the set teardown complete buffer descriptor bit. The port does not clear any channel
enables due to a teardown command. A teardown command to an inactive channel issues an interrupt
that software should acknowledge with a 0xfffffffc acknowledge value (note that there is no buffer
descriptor in this case). Software may read the interrupt acknowledge location to determine if the interrupt
was due to a commanded teardown. The read value will be 0xfffffffc if the interrupt was due to a teardown
command.
14.3.2.4.3 Transmit DMA Interface
The Transmit DMA is an eight channel CPPI 3.0 compliant interface. Priority between the eight queues
may be either fixed or round robin as selected by tx_ptype in the DMAControl register. If the priority type is
fixed, then channel 7 has the highest priority and channel 0 has the lowest priority. Round robin priority
proceeds from channel 0 to channel 7. Packet Data transfers occur on the TX_VBUSP interface in 64-
byte maximum burst transfers
14.3.2.4.3.1 Transmit DMA Host Configuration
To configure the TX DMA for operation the host must do the following:
•
Initialize the Tx_HDP registers to a zero value.
•
Enable the desired transmit interrupts in the IntMask register.
•
Setup the transmit channel(s) buffer descriptors in host memory as defined in CPPI 3.0.
•
Configure and enable the transmit operation as desired in the TxControl register.
•
Write the appropriate Tx_HDP registers with the appropriate values to start transmit operations.
14.3.2.4.3.2 Transmit Channel Teardown
The host commands a transmit channel teardown by writing the channel number to the Tx_Teardown
register. When a teardown command is issued to an enabled transmit channel the following will occur:
•
Any frame currently in transmission will complete normally
•
The teardown complete bit will be set in the next sop buffer descriptor (if there is one).
•
The channel head descriptor pointer will be set to zero.
•
An interrupt will be issued to inform the host of the channel teardown.
•
The host should acknowledge a teardown interrupt with a 0xfffffffc acknowledge value
Channel teardown may be commanded on any channel at any time. The host is informed of the teardown
completion by the set teardown complete buffer descriptor bit. The port does not clear any channel
enables due to a teardown command. A teardown command to an inactive channel issues an interrupt
that software should acknowledge with a 0xfffffffc acknowledge value (note that there is no buffer
descriptor in this case). Software may read the interrupt acknowledge location to determine if the interrupt
was due to a commanded teardown. The read value will be 0xfffffffc if the interrupt was due to a teardown
command.
14.3.2.4.4 Transmit Rate Limiting
Transmit operations can be configured to rate limit the transmit data for each transmit priority. Rate limiting
is enabled for a channel when the tx_rlim[7:0] bit associated with that channel is set in the DMAControl
register. Rate limited channels must be the highest priority channels. For example, if two rate limited
channels are required then tx_rlim[7:0] should be set to 11000000 with the msb corresponding to channel
7.
When any channels are configured to be rate-limiting, the priority type must be fixed for transmit. Round-
robin priority type is not allowed when rate-limiting. Each of the eight transmit priorities has an associated
register to control the rate at which the priority is allowed to send data (Tx_Pri(7..0)_Rate) when the
channel is rate-limiting. Each priority has a send count (pri(7..0)_send_cnt[13:0]) and an idle count
(pri(7..0)_idle_cnt[13:0]). The transfer rate includes the inter-packet gap (12 bytes) and the preamble (8
bytes). The rate in Mbits/second that each priority is allowed to send is controlled by the below equation.
Priority Transfer rate in Mbit/s = ((priN_idle_cnt/(priN_id priN_send_cnt)) * frequency * 32
1193
SPRUH73H – October 2011 – Revised April 2013
Ethernet Subsystem
Copyright © 2011–2013, Texas Instruments Incorporated