PCIE协议解析 synopsys IP DBI and LBC 读书笔记(5) |
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5.1 Local Bus Controller (LBC) and Data Bus Interface (DBI)(重要)
5.1.1 Overview
LBC module DBI接口可以对其进行访问,没有任何限制,需要注意的是: Ø 在RC模式下,LBC只能通过DBI接口访问 Ø 而在EP 模式下,远程设备也可以访问。 LBC可以访问的区域有2个部分: Ø 内部的寄存器(CDM) Ø 外部的应用寄存器,通过ELBI连接 Core包含4096个寄存器,分为PCIeconfiguration 和Port logicper function两个大块,这些空间DBI可以无限制访问,而在EP模式下,远程设备可以通过CFG request访问,而prot logic 和 ELBI控制的用户register 同样可以通过BAR Match MEM 和 IO request 访问。
5.1.2 CDM/ELBI Register Space Layout 注意:wire access(Upstream portonly 也就是只能写,不能读?????) Ø CFGCONFIG_LIMIT时,访问ELBI Ø 任何的通过BAR capture的MEM/IOrequest目标空间都是通过TRGT0访问ELBI的外部应用register DBI(upstream 和 downstream port) Ø 没有MEM/IO/CFG等概念 Ø 通过特殊的bit为决定是访问ELBI还是CDM Ø 没有对于空间是否能够访问的仲裁,也就是整个空间可以无限制读写。 PCI Configuration Header and Capability Registers (in CDM)PCI configuration header 和 capability register 都是PCIe的内核配置的标准寄存器,由the PCI Express3.0 Specification定义,可以通过PCIe wire 的CFGrequest访问(EP mode only)。DBI可以无限制访问。
注: Ø 在EP mode,通过PCIe wire: l 你可以memory-map Port logic register 的space。(是否指可以从新map这段寄存器的地址???)。 l 你不可以memory-map PCI和PCIe configuration register 的space。你必须通过CFGrequest 访问该区域 Ø 在RC mode下,访问CDM只可以通过DBI,PCIe wire 不允许访问CDM。 Ø DBI接口无限制访问CDM。 Port Logic Registers (in CDM)Port logic register是synopsys定义的空间,该部分的寄存器在PCI Express 3.0 specification中并没有定义,在EPmode下,可以接受PCIewire 的CFG request,但是在RC mode 下,PCIe wire的访问将不被允许,DBI接口可以无限制访问。 External Register Access (ELBI)用户的applicationregister 是在core的外部的,通过ELBI连接,可以接受 PCIe wire的CFG、EME、IO request,但是相同的,在RC mode下不允许。同样DBI接口可以无限制访问。 Ø 对ELBI 访问的特征和限制可以参考see “Features andLimitations” on page 90. Ø ELBI在32bit位宽的情况下可以支持4GB的application register的空间 For more details, see K:, “Advanced LBC and DBI Usage” and “External Local Bus Interface(ELBI)” on page 238. 5.1.3 PCIe Wire Access (EP Mode)注意:对于wire access Ø 对于ELBI space的IO 和MEM request ,需要将MEM_FUNCN_BARn_TARGET_MAP置0 Ø 对于ELBI 的CFG request,通过CONFIG_LIMIT andTARGET_ABOVE_CONFIG_LIMIT两个条件决定 Ø Port logic 的MEM request,采用ENABLE_MEM_MAP_PL_REG 架构,具体参见see K:, “AdvancedLBC and DBI Usage”. 在默认情况下,所有的到达PCIconfiguration space和Port logic register 的请求都来自TRGT0,并通过LBC到达CDM。在默认的情况下,没有ELBI的访问可以到达,因为 CONFIG_LIMIT的默认值为0x3FF,(位于CFG register 地址的顶端)。!!!!!!!!!!使用的时候要特别的注意一下。 5.1.4 PCIe Wire Access (RCMode) 5.1.5 DBI Access DBI可以无限制访问所有4096 byte的寄存器空间。 Native Core DBI AccessDBI地址位的最低一位为CDM和ELBI的选择位。 AHB/AXI Dedicated DBI Access 暂时可以不关注 AXI Shared DBI Access暂时可以不关注 5.1.5.1 Native Core DBI To CDM/ELBI Access Details■ The DBI address must be a DWORD address with dbi_addr[1]=1’b0. The LSB (dbi_addr[0]) can then be used to select between CDM(0) andELBI(1) access. ■ Byte access within a DWORD for write requests is possibleusing dbi_wr[3:0]. ■ The dbi_wr[3:0] bus alsoidentifies the type of access as a write or read (4’h0). 5.1.6 Features andLimitations The following limitations exist for the LBC. ■ CDM Access Restrictions: ❑ Maximumpayload Length =1 DWORD. ❑ PCIe MEM requestswith Length > 1 are processed as completer abort. ❑ PCIe MEMrequests with Length =0 are processed as completer abort. ❑ PCIe IO orCFG requests with Length !=1 are processed as malformed TLPs. ■ ELBI Access Restrictions: ❑ Maximumpayload Length = CX_LBC_NW(1 or 2DWORDs). ❑ PCIe MEMrequests with Length > CX_LBC_NW are processed as completer abort. ❑ PCIe MEMrequests with Length =0 are processed as completer abort. ❑ PCIe IO orCFG requests with Length !=1 are processed as malformed TLPs. ❑ Address mustbe CX_LBC_NW aligned. ❑ Does notsupport “AtomicOperations (AtomicOps)” on page 215. ❑ Does notsupport TPH. Core does not forward the TPH bits to the ELBI. ■ ELBI Data/Address Port Width Restrictions: ❑ Data(Write): CX_LBC_NW= 1 or 2DWORDs. ❑ Data (Read):CX_LBC_NW = 1 or 2 DWORDs per function. ❑ Coredatapath width (CX_NW) must be>= CX_LBC_NW. ❑ Address: CX_LBC_EXT_AW= 12-32. It is expected that your application at the ELBI only decodes the validaddress bits to the BAR limit specified. ■ DBI Data/Address Port Widths (with no AHB/AXI bridge): ❑ Data: 32 bit ❑ Address: 32bit ■ DBI accesses are not supported when the core is in any ofthe low-power states that allow core_clk
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