Electronic Components Datasheet Search |
|
DP83934 Datasheet(PDF) 28 Page - Texas Instruments |
|
DP83934 Datasheet(HTML) 28 Page - Texas Instruments |
28 / 106 page 50 Buffer Management (Continued) 542 Receive Buffer Area (RBA) The SONIC-T stores the actual data of a received packet in the RBA The RBAs are designated by the Resource De- scriptors in the RRA as described above The RXrsrcbuff wc01 fields of the RRA indicate the length of the RBA When the SONIC-T gets an RBA from the RRA the RXrsrcbuff wc01 values are loaded into the Remaining Buffer Word Count registers (RBWC01) These registers keep track of how much space (in words) is left in the buffer When a packet is buffered in a RBA it is buffered contigu- ously (the SONIC-T will not scatter a packet into multiple buffers or fragments) Therefore if there is not enough space left in a RBA after buffering a packet to buffer at least one more maximum sized packet (the maximum legal sized packet expected to be received from the network) a new buffer must be acquired The End of Buffer Count (EOBC) register is used to tell the SONIC-T the maximum packet size that the SONIC-T will need to buffer 5421 End of Buffer Count (EOBC) The EOBC is a boundary in the RBA based from the bottom of the buffer The value written into the EOBC is the maxi- mum expected size (in words) of the network packet that the SONIC-T will have to buffer This word count creates a line in the RBA that when crossed causes the SONIC-T to fetch a new RBA resource from the RRA Note The EOBC is a word count not a byte count Also the value pro- grammed into EOBC must be a double word (32-bit) quantity when the SONIC-T is in 32-bit mode (eg in 32-bit mode EOBC should be set to 760 words not 759 words even though the maximum size of an IEEE 8023 packet is 759 words for double work boundary align- ment) 5422 Buffering the Last Packet in an RBA At the start of reception the SONIC-T stores the packet beginning at the Current Receive Buffer Address (CRBA01) and continues until the reception is complete Concurrent with reception the SONIC-T decrements the Remaining Buffer Word Count (RBWC01) by one in 16-bit mode or by two in 32-bit mode At the end of reception if the packet has crossed the EOBC boundary the SONIC-T knows that the next packet might not fit in the RBA This check is done by comparing the RBWC01 registers with the EOBC If RBWC01 is less than the EOBC (the last packet buffered has crossed the EOBC boundary) the SONIC-T fetches the next resource descriptor in the RRA If RBWC01 is greater than or equal to the EOBC (the EOBC boundary has not been crossed) the next packet reception continues at the present location pointed to by CRBA01 in the same RBA Figure 5-5 illustrates the SONIC-T’s actions for (1) RBWC01 t EOBC and (2) RBWC01 k EOBC See Sec- tion 5444 for specific information about setting the EOBC Note It is important that the EOBC boundary be ‘‘crossed’’ In other words case 1in Figure 5-5 must exist before case 2 exists If case 2 occurs without case 1 having occurred first the test for RBWC01 k EOBC will not work properly and the SONIC-T will not fetch a new buffer The result of this will be a buffer overflow (RBAE in the Inter- rupt Status Register Section 636) TLF11719 – 17 FIGURE 5-4 Receive Resource Area Format TLF11719 – 18 Case 1 Case 2 (RBWC01 t EOBC) (RBWC01 k EOBC) Case 1 SONIC-T buffers next packet in same RBA Case 2 SONIC-T detects an exhausted RBA and will buffer the next packet in another RBA FIGURE 5-5 Receive Buffer Area 27 |
Similar Part No. - DP83934 |
|
Similar Description - DP83934 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |