Open BMC开发系列（十）配置串口可以输出BIOS信息

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最近一直在搞open BMC的串口问题，费了很长时间，主要原因还是不熟。

问题描述：

        我们使用浪潮的BMC，对应板子的串口可以正常输出BIOS的启动过程，但是使用我这个分支的BMC，串口并不能输出BIOS对应的启动信息。

分析过程：

        从问题可知，问题出在BMC侧，BIOS已经完成了重定向的设置。

        BMC上的串口组件是UART，对应的串口控制器描述如下：

39 UART Controller (16550) 39.1 Overview AST2500 integrates 5 sets of UART (Universal Asynchronous Receiver/Transmitter) providing serial commu nication capabilities with other external devices, like another computer using a serial cable based on RS232 protocol. This core is designed to be compatible with the industry standard — 16550 UART. The two sets of UART are equipped with a 16x8 FIFO that can be programmed to be enabled or disabled. The supported baud rates are also programmable. Each unit of UART totally implements 12 sets of 32-bit registers, which are listed below, to program the various supported functions including character length selection, baud rate selection, interrupt generation, and parity generation/checking. Each register has its own specifific offset value, ranging from 0x00 to 0x14h, to derive its physical address location. Base Address of UART1 = 0x1E78 3000 Base Address of UART2 = 0x1E78 D000 Base Address of UART3 = 0x1E78 E000 Base Address of UART4 = 0x1E78 F000 Base Address of UART5 = 0x1E78 4000 Register Address of UART = (Base Address of UART) + Offset UART RBR : Receiving Buffer Register (DLAB = 0) UART THR : Transmit Holding Register (DLAB = 0) UART IER : Interrupt Enable Register (DLAB = 0) UART IIR : Interrupt Identity Register UART FCR : FIFO Control Register UART LCR : Line Control Register UART MCR : Modem Control Register UART LSR : Line Status Register UART MSR : Modem Status Register UART SCR : Scratch Register UART DLL : Divisor Latch Low Register : (DLAB = 1) UART DLH : Divisor Latch High Register : (DLAB = 1)

39.2 Features • Directly connected to APB bus ASPEED Confifidential All rights reserved. 631 May 12, 2017 ASPEED Confifidential ASPEED AST2500/AST2520 A2 Datasheet – V1.6 • Support two UART with full flflow control pins (one is with dedicated flflow control pins, the other is shared with GPIO pins) • Separate transmit & receive FIFO buffer (16x8) to reduce CPU interrupts • Support up to 115.2K baud-rate • Programmable baud rate generator • Standard asynchronous communication bits — Stat/Stop/Parity • Independent masking of transmit FIFO, receive FIFO, receiving timeout and error condition Interrupts • False start-bit detection • Line break generation and detection • Fully programmable serial interface characteristics: – 5/6/7/8 data length – Even, odd and none parity generation and detection – 1/2 stop-bit generation • Extended diagnostic Loopback Mode allows testing more Modem Control and Auto Flow Control features

        ast2500支持5组串口，12个寄存器。所以我需要先知道板子上的定向输出BIOS的串口是哪一个口，经过查询可知为串口1。         拿到串口后，查询设备树，发现设备树确实没有添加uart1，导致串口不能用。我首先想到的的是enable uart 1，即在设备树添加：

&uart1 {
    status = "okay"; }

        添加完以后，串口依旧不能输出对应的BIOS信息，但是通过跳线（先用浪潮的BMC启动，再跳线切到我的bmc），发现串口可以输出了。         到这里，说明，我的串口应该还有一些初始化配置未能加载和操作，导致输出不了启动信息。到这里只能求助到浪潮的工作人员，让他们发送串口1的设备树配置过来，看看结果。         最后，终于拿到了串口1的设备树信息：

&uart1 {
    /* Rear RS-232 connector */
    status = "okay";
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_txd1_default
            &pinctrl_rxd1_default
            &pinctrl_nrts1_default
            &pinctrl_ndtr1_default
            &pinctrl_ndsr1_default
            &pinctrl_ncts1_default
            &pinctrl_ndcd1_default
            &pinctrl_nri1_default>;
};

        添加到设备树，通信正常。从配置看，是配置了pin脚，pinctrl的具体配置我也没看懂，有看懂的朋友留言交流。

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本文标签： 串口系列信息OpenBMC