From 7f8b5a20fae8a0eb387f96fbb17d858c266cd067 Mon Sep 17 00:00:00 2001 From: yuchen Date: Fri, 13 Mar 2015 20:21:44 +0800 Subject: [PATCH] update console.c for more info about CGA and 6845 chip --- labcodes/lab1/kern/driver/console.c | 34 ++++++++++++++++++++++------------ 1 file changed, 22 insertions(+), 12 deletions(-) diff --git a/labcodes/lab1/kern/driver/console.c b/labcodes/lab1/kern/driver/console.c index 8ab42b8..477604e 100644 --- a/labcodes/lab1/kern/driver/console.c +++ b/labcodes/lab1/kern/driver/console.c @@ -53,29 +53,39 @@ static uint16_t crt_pos; static uint16_t addr_6845; /* TEXT-mode CGA/VGA display output */ - +// 显示器初始化，CGA 是 Color Graphics Adapter 的缩写 +// CGA显存按照下面的方式映射： +// -- 0xB0000 - 0xB7777 单色字符模式 +// -- 0xB8000 - 0xBFFFF 彩色字符模式及 CGA 兼容图形模式 +// 6845芯片是IBM PC中的视频控制器 +// CPU通过IO地址0x3B4-0x3B5来驱动6845控制单色显示，通过IO地址0x3D4-0x3D5来控制彩色显示。 +// -- 数据寄存器 映射 到 端口 0x3D5或0x3B5 +// -- 索引寄存器 0x3D4或0x3B4,决定在数据寄存器中的数据表示什么。 static void cga_init(void) { - volatile uint16_t *cp = (uint16_t *)CGA_BUF; - uint16_t was = *cp; + volatile uint16_t *cp = (uint16_t *)CGA_BUF; //CGA_BUF: 0xB8000 (彩色显示的显存物理基址) + uint16_t was = *cp; //保存当前光标所在值 *cp = (uint16_t) 0xA55A; if (*cp != 0xA55A) { - cp = (uint16_t*)MONO_BUF; - addr_6845 = MONO_BASE; + cp = (uint16_t*)MONO_BUF; //黑白显示的显存基址 MONO_BUF： 0xB0000 + addr_6845 = MONO_BASE; //黑白显示控制的IO地址，MONO_BASE: 0x3B4 } else { - *cp = was; - addr_6845 = CGA_BASE; + *cp = was; //还原原来的光标所在值 + addr_6845 = CGA_BASE; // 彩色显示控制的IO地址， CGA_BASE: 0x3D4 } // Extract cursor location + // 6845索引寄存器的index 0x0E（及十进制的14）== 光标位置(高位) + // 6845索引寄存器的index 0x0F（及十进制的15）== 光标位置(低位) + // 6845 reg 15 : Cursor Address (Low Byte) uint32_t pos; - outb(addr_6845, 14); - pos = inb(addr_6845 + 1) << 8; + outb(addr_6845, 14); + pos = inb(addr_6845 + 1) << 8; //读出了光标位置(高位) outb(addr_6845, 15); - pos |= inb(addr_6845 + 1); + pos |= inb(addr_6845 + 1); //读出了光标位置(低位) - crt_buf = (uint16_t*) cp; - crt_pos = pos; + crt_buf = (uint16_t*) cp; //crt_buf是CGA显存起始地址 + crt_pos = pos; //crt_pos是CGA当前光标位置 } static bool serial_exists = 0;