TX4939XBG-400 Toshiba, TX4939XBG-400 Datasheet - Page 508

• Manufacturer Part Number: TX4939XBG-400
• Manufacturer: Toshiba

Specifications of TX4939XBG-400

• Cpu Core: TX49/H4 90nm
• Clock Mhz/max Mips: 400/520
• Inst./data Cache: 32KB (4 Way)/32KB (4 Way)
• Tlb: x
• 1cycle Mac: x
• Volts (v): 1.25/2.5/3.3
• Peripherals: DDR, NAND, ATA, ETHERNET, SECURITY, FPU, MMU, SPI, I2S, I2C, PCI, VIDEO, UART, TIMER, RTC
• Companion Chip: TC86C001FG
• Package: PGBA456

EMAC
18.3.7.1.1. FDNext field (next frame descriptor)
The FDNext field stores a flag that indicates the end of list (EOL) or a pointer to the next frame descriptor in the same
queue. The frame descriptor must be aligned to a 16-byte boundary. In other words, bits 0-3 of the valid pointer must be
"0".
Regardless of the queue type, by setting the EOL bit, you can use the FDNext field stop the list consumer (consumption
side processing mechanism). The consumer must wait for the list producer (generation side processing mechanism) to
clear the EOL bit and store a valid pointer. In the case of a buffer list queue, you can use the FDNext field to create a
chain to the next buffer pool from any buffer pool. When not creating a buffer list chain, the software driver has to set its
own address in the FDNext field. Doing so makes it possible for the Ethernet Controller to recheck so it can reuse the
same buffer area. You can also set the EOL bit and stop the Ethernet Controller.
18.3.7.1.2. FDSystem field (frame descriptor system data)
The FDSystem field is a 32-bit field that is reserved for use by the system software. You can use this field to store
pointers to the information table, pointers to C++ virtual functions, etc.
The Transmission queue does not use the FDSystem field.
In the case of a Reception queue, the Ethernet Controller copies the content of the FDSystem field of a frame descriptor
that retains a buffer list to which is allocated the first buffer descriptor that stores the frame.
18.3.7.1.3. FDStat field (frame descriptor status)
The Transmission queue or Reception queue uses the FDStat field to display the transmission/reception complete status.
For the meaning of each Status bit, see the descriptions of the TX_Stat Register and Rx_Stat Register in subsection
18.4.5 MAC Control, Status Register group.
The reception empty buffer list does not use the FDStat field.
18.3.7.1.4. FDLength field (frame descriptor length)
The Transmission queue does not use the FDLength field.
In the case of the Reception queue, the Ethernet Controller sets the FDLength field to the total packet length.
In the case of a buffer list, the FDLength field is used to count the number of empty buffer descriptors allocated to the
queue. The Ethernet Controller accesses the buffer list frame descriptor through the Buffer List Frame Pointer Register.
When the Ethernet Controller encounters a buffer that it does not own, it sets the BL_Ex bit of the Interrupt Source
Register and then waits for the system to clear it. The Ethernet Controller treats the FDLength field value as the upper
limit, then reads the buffer descriptor. As the Ethernet Controller nears the end of the list, it reads out the next frame
descriptor that the FDNext field indicates, as described in 18.4.3.8 Free Descriptor Area (FDA) Register.
Rev. 3.1 November 1, 2005
Bit(s)
31 : 4
3 : 1
0
31
15
Mnemonic
Pointer
EOL
Field Name
28-bit Pointer
End Of List flag
Pointer
Description
28 bit Pointer
When EOL=0, the upper 28 bits of the address of the next frame descriptor in this
queue is stored.
Is fixed to 000
EOL
0:
1:
Figure 18-6 FDNext Field
Pointer is valid.
End of list. You have to wait until this flag is cleared.
18-16
Pointer
4
Toshiba RISC Processor
3
0
0
1
0
EOL
16
TX4939
0
18
18