摘要：DS31256 Envoy HDLC控制器在發送數據包之前的初始化順序。

概述

按照設計，DS31256上電以后不會控制PCI總線。所有的物理端口(端口0至15)發送全1 (非HDLC空閑碼)，因此在上電之后DS31256處于空閑狀態。另一方面，DS31256可以初始化基于RAM的存儲器，包括直接和間接的，用于存儲內部狀態機的狀態。DS31256有許多非常復雜的狀態機和相互作用的功能模塊，因此上電之后，在發送和接收任何數據包之前，所有的這些內部寄存器/RAM必須初始化到一個已知狀態。建議使用者在發送數據包之前按照表1的步驟進行初始化。

表1. DS31256的初始化步驟

Initialization Step	Comments
1. System reset.	System reset can be invoked by either hardware action via the PRST-bar signal or software action via the RST control bit in the Master Reset and ID register; all the internal device configuration registers are set to zero (0000h).
2. Configure Local Bus Bridge Mode Control register (LBBMC), if DS31256 is used in bridge mode.	Please note that these registers are not affected by a software-invoked system reset. It will be forced to all zeros only by hardware reset.
3. Initialize the PCI configuration registers.	Achieved by asserting the PIDSEL signal.
4. Master software reset.	Master software reset in MRID register.
5. Initialize all indirect registers to zero.	It is recommended that all the indirect registers be set to 0000h. See Table 2 for a list of all indirect registers.
6. Master software reset.	Master software reset in MRID register.
7. Configure the device for operation.	Program all the necessary registers, which includes the Layer One, HDLC, FIFO, and DMA registers, but except: 1. Ports are disabled; keep layer-one ports off by leaving the TFDA1 bits to 0 (default state) in TP[n]CR register. 2. HDLC channels are disabled. 3. DMA and DMA channels are disabled. 4. In high-speed unchannelized mode, set it to low-speed unchannelized mode in the RP[n]CR register and enable it to high-speed unchannelized mode in Step 12 (see below).
8. Enable the HDLC channels.	Done via the RCHEN and TCHEN bits in the R[n]CFG[j] and T[n]CFG[j] registers.
9. Load the DMA descriptors.	Indicate to the DMA where packet data can be written and where pending data (if any) resides.
10. Enable the DMAs.	Done via the RDE and TDE control bits in the Master Configuration (MC) register.
11. Enable DMA for each HDLC channel.	Done via the channel-enable bit in the receive and transmit configuration RAM.
12. Turns on HDLC channels.	Enable and allow ports to transmit normally, set TFDA1 bits to 1 in TP[n]CR registers. Note: For high-speed unchannelized mode only, enable high-speed unchannelized in RP[n]CR register.
13. Wait enough time for all configurations to take effect.	It is going to take a minimum of 500μs or 768 RC and TC clock cycles (which ever is longer) before packet data can be processed.

注意：建議DS31256上電之后進行 “硬件復位”。

表2. 間接寄存器

Offset/Address	Register Name	Number of Indirect Registers	Data Sheet Section
0x3xx	Channelized Port Data Indirect Select (CP0RDIS to CP15RDIS)	6144 (16 Ports x 128 DS0 Channels x 3 Registers for each DS0 Channel)	6.3
0x400	Receive HDLC Channel Definition Indirect Select (RHCDIS)	256 (one for each HDLC Channel)	7.2
0x480	Transmit HDLC Channel Definition Indirect Select (THCDIS)	256 (one for each HDLC Channel)	7.2
0x770	Receive DMA Configuration Indirect Select (RDMACIS)	1536 (one for each HDLC Channel)	9.3.5
0x870	Transmit DMA Configuration Indirect Select (TDMACIS)	3072 (one for each HDLC Channel)	9.3.5
0x900	Receive FIFO Staring Block Pointer Indirect Select (RFSBPIS)	256 (one for each HDLC Channel)	8.2
0x910	Receive FIFO Block Pointer Indirect Select (RFBPIS)	1024 (one for each FIFO Block)	8.2
0x920	Receive FIFO High Watermark Indirect Select (RFHWMIS)	256 (one for each HDLC Channel)	8.2
0x980	Transmit FIFO Staring Block Pointer (TFSBPIS)	256 (one for each HDLC Channel)	8.2
0x990	Transmit FIFO Block Pointer Indirect Select (TFBPIS)	1024 (one for each FIFO Block)	8.2
0x9A0	Transmit FIFO Low Watermark Indirect Select (TFLWMIS)	256 (one for each HDLC Channel)	8.2