setup.htm

这是一个Linux内核。是0.11版本的

<a name=L108 href="source/boot/setup.s#L108">108</a> 
<a name=L109 href="source/boot/setup.s#L109">109</a>         cli                     ! no interrupts allowed !
<a name=L110 href="source/boot/setup.s#L110">110</a> 
<a name=L111 href="source/boot/setup.s#L111">111</a> ! first we move the system to it's rightful place
<a name=L112 href="source/boot/setup.s#L112">112</a> 
<a name=L113 href="source/boot/setup.s#L113">113</a>         mov     ax,#0x0000
<a name=L114 href="source/boot/setup.s#L114">114</a>         cld                     ! 'direction'=0, movs moves forward
<a name=L115 href="source/boot/setup.s#L115">115</a> do_move:
<a name=L116 href="source/boot/setup.s#L116">116</a>         mov     es,ax           ! destination segment
<a name=L117 href="source/boot/setup.s#L117">117</a>         add     ax,#0x1000
<a name=L118 href="source/boot/setup.s#L118">118</a>         cmp     ax,#0x9000
<a name=L119 href="source/boot/setup.s#L119">119</a>         jz      end_move
<a name=L120 href="source/boot/setup.s#L120">120</a>         mov     ds,ax           ! source segment
<a name=L121 href="source/boot/setup.s#L121">121</a>         sub     di,di
<a name=L122 href="source/boot/setup.s#L122">122</a>         sub     si,si
<a name=L123 href="source/boot/setup.s#L123">123</a>         mov     cx,#0x8000
<a name=L124 href="source/boot/setup.s#L124">124</a>         rep
<a name=L125 href="source/boot/setup.s#L125">125</a>         movsw
<a name=L126 href="source/boot/setup.s#L126">126</a>         jmp     do_move
<a name=L127 href="source/boot/setup.s#L127">127</a> 
<a name=L128 href="source/boot/setup.s#L128">128</a> ! then we load the segment descriptors
<a name=L129 href="source/boot/setup.s#L129">129</a> 
<a name=L130 href="source/boot/setup.s#L130">130</a> end_move:
<a name=L131 href="source/boot/setup.s#L131">131</a>         mov     ax,#SETUPSEG    ! right, forgot this at first. didn't work :-)
<a name=L132 href="source/boot/setup.s#L132">132</a>         mov     ds,ax
<a name=L133 href="source/boot/setup.s#L133">133</a>         lidt    idt_48          ! load idt with 0,0
<a name=L134 href="source/boot/setup.s#L134">134</a>         lgdt    gdt_48          ! load gdt with whatever appropriate
<a name=L135 href="source/boot/setup.s#L135">135</a> 
<a name=L136 href="source/boot/setup.s#L136">136</a> ! that was painless, now we enable A20
<a name=L137 href="source/boot/setup.s#L137">137</a> 
<a name=L138 href="source/boot/setup.s#L138">138</a>         call    empty_8042
<a name=L139 href="source/boot/setup.s#L139">139</a>         mov     al,#0xD1                ! command write
<a name=L140 href="source/boot/setup.s#L140">140</a>         out     #0x64,al
<a name=L141 href="source/boot/setup.s#L141">141</a>         call    empty_8042
<a name=L142 href="source/boot/setup.s#L142">142</a>         mov     al,#0xDF                ! A20 on
<a name=L143 href="source/boot/setup.s#L143">143</a>         out     #0x60,al
<a name=L144 href="source/boot/setup.s#L144">144</a>         call    empty_8042
<a name=L145 href="source/boot/setup.s#L145">145</a> 
<a name=L146 href="source/boot/setup.s#L146">146</a> ! well, that went ok, I hope. Now we have to reprogram the interrupts :-(
<a name=L147 href="source/boot/setup.s#L147">147</a> ! we put them right after the intel-reserved hardware interrupts, at
<a name=L148 href="source/boot/setup.s#L148">148</a> ! int 0x20-0x2F. There they won't mess up anything. Sadly IBM really
<a name=L149 href="source/boot/setup.s#L149">149</a> ! messed this up with the original PC, and they haven't been able to
<a name=L150 href="source/boot/setup.s#L150">150</a> ! rectify it afterwards. Thus the bios puts interrupts at 0x08-0x0f,
<a name=L151 href="source/boot/setup.s#L151">151</a> ! which is used for the internal hardware interrupts as well. We just
<a name=L152 href="source/boot/setup.s#L152">152</a> ! have to reprogram the 8259's, and it isn't fun.
<a name=L153 href="source/boot/setup.s#L153">153</a> 
<a name=L154 href="source/boot/setup.s#L154">154</a>         mov     al,#0x11                ! initialization sequence
<a name=L155 href="source/boot/setup.s#L155">155</a>         out     #0x20,al                ! send it to 8259A-1
<a name=L156 href="source/boot/setup.s#L156">156</a>         .word   0x00eb,0x00eb           ! jmp $+2, jmp $+2
<a name=L157 href="source/boot/setup.s#L157">157</a>         out     #0xA0,al                ! and to 8259A-2
<a name=L158 href="source/boot/setup.s#L158">158</a>         .word   0x00eb,0x00eb
<a name=L159 href="source/boot/setup.s#L159">159</a>         mov     al,#0x20                ! start of hardware int's (0x20)
<a name=L160 href="source/boot/setup.s#L160">160</a>         out     #0x21,al
<a name=L161 href="source/boot/setup.s#L161">161</a>         .word   0x00eb,0x00eb
<a name=L162 href="source/boot/setup.s#L162">162</a>         mov     al,#0x28                ! start of hardware int's 2 (0x28)
<a name=L163 href="source/boot/setup.s#L163">163</a>         out     #0xA1,al
<a name=L164 href="source/boot/setup.s#L164">164</a>         .word   0x00eb,0x00eb
<a name=L165 href="source/boot/setup.s#L165">165</a>         mov     al,#0x04                ! 8259-1 is master
<a name=L166 href="source/boot/setup.s#L166">166</a>         out     #0x21,al
<a name=L167 href="source/boot/setup.s#L167">167</a>         .word   0x00eb,0x00eb
<a name=L168 href="source/boot/setup.s#L168">168</a>         mov     al,#0x02                ! 8259-2 is slave
<a name=L169 href="source/boot/setup.s#L169">169</a>         out     #0xA1,al
<a name=L170 href="source/boot/setup.s#L170">170</a>         .word   0x00eb,0x00eb
<a name=L171 href="source/boot/setup.s#L171">171</a>         mov     al,#0x01                ! 8086 mode for both
<a name=L172 href="source/boot/setup.s#L172">172</a>         out     #0x21,al
<a name=L173 href="source/boot/setup.s#L173">173</a>         .word   0x00eb,0x00eb
<a name=L174 href="source/boot/setup.s#L174">174</a>         out     #0xA1,al
<a name=L175 href="source/boot/setup.s#L175">175</a>         .word   0x00eb,0x00eb
<a name=L176 href="source/boot/setup.s#L176">176</a>         mov     al,#0xFF                ! mask off all interrupts for now
<a name=L177 href="source/boot/setup.s#L177">177</a>         out     #0x21,al
<a name=L178 href="source/boot/setup.s#L178">178</a>         .word   0x00eb,0x00eb
<a name=L179 href="source/boot/setup.s#L179">179</a>         out     #0xA1,al
<a name=L180 href="source/boot/setup.s#L180">180</a> 
<a name=L181 href="source/boot/setup.s#L181">181</a> ! well, that certainly wasn't fun :-(. Hopefully it works, and we don't
<a name=L182 href="source/boot/setup.s#L182">182</a> ! need no steenking BIOS anyway (except for the initial loading :-).
<a name=L183 href="source/boot/setup.s#L183">183</a> ! The BIOS-routine wants lots of unnecessary data, and it's less
<a name=L184 href="source/boot/setup.s#L184">184</a> ! "interesting" anyway. This is how REAL programmers do it.
<a name=L185 href="source/boot/setup.s#L185">185</a> !
<a name=L186 href="source/boot/setup.s#L186">186</a> ! Well, now's the time to actually move into protected mode. To make
<a name=L187 href="source/boot/setup.s#L187">187</a> ! things as simple as possible, we do no register set-up or anything,
<a name=L188 href="source/boot/setup.s#L188">188</a> ! we let the gnu-compiled 32-bit programs do that. We just jump to
<a name=L189 href="source/boot/setup.s#L189">189</a> ! absolute address 0x00000, in 32-bit protected mode.
<a name=L190 href="source/boot/setup.s#L190">190</a> 
<a name=L191 href="source/boot/setup.s#L191">191</a>         mov     ax,#0x0001      ! protected mode (PE) bit
<a name=L192 href="source/boot/setup.s#L192">192</a>         lmsw    ax              ! This is it!
<a name=L193 href="source/boot/setup.s#L193">193</a>         jmpi    0,8             ! jmp offset 0 of segment 8 (cs)
<a name=L194 href="source/boot/setup.s#L194">194</a> 
<a name=L195 href="source/boot/setup.s#L195">195</a> ! This routine checks that the keyboard command queue is empty
<a name=L196 href="source/boot/setup.s#L196">196</a> ! No timeout is used - if this hangs there is something wrong with
<a name=L197 href="source/boot/setup.s#L197">197</a> ! the machine, and we probably couldn't proceed anyway.
<a name=L198 href="source/boot/setup.s#L198">198</a> empty_8042:
<a name=L199 href="source/boot/setup.s#L199">199</a>         .word   0x00eb,0x00eb
<a name=L200 href="source/boot/setup.s#L200">200</a>         in      al,#0x64        ! 8042 status port
<a name=L201 href="source/boot/setup.s#L201">201</a>         test    al,#2           ! is input buffer full?
<a name=L202 href="source/boot/setup.s#L202">202</a>         jnz     empty_8042      ! yes - loop
<a name=L203 href="source/boot/setup.s#L203">203</a>         ret
<a name=L204 href="source/boot/setup.s#L204">204</a> 
<a name=L205 href="source/boot/setup.s#L205">205</a> gdt:
<a name=L206 href="source/boot/setup.s#L206">206</a>         .word   0,0,0,0         ! dummy
<a name=L207 href="source/boot/setup.s#L207">207</a> 
<a name=L208 href="source/boot/setup.s#L208">208</a>         .word   0x07FF          ! 8Mb - limit=2047 (2048*4096=8Mb)
<a name=L209 href="source/boot/setup.s#L209">209</a>         .word   0x0000          ! base address=0
<a name=L210 href="source/boot/setup.s#L210">210</a>         .word   0x9A00          ! code read/exec
<a name=L211 href="source/boot/setup.s#L211">211</a>         .word   0x00C0          ! granularity=4096, 386
<a name=L212 href="source/boot/setup.s#L212">212</a> 
<a name=L213 href="source/boot/setup.s#L213">213</a>         .word   0x07FF          ! 8Mb - limit=2047 (2048*4096=8Mb)
<a name=L214 href="source/boot/setup.s#L214">214</a>         .word   0x0000          ! base address=0
<a name=L215 href="source/boot/setup.s#L215">215</a>         .word   0x9200          ! data read/write
<a name=L216 href="source/boot/setup.s#L216">216</a>         .word   0x00C0          ! granularity=4096, 386
<a name=L217 href="source/boot/setup.s#L217">217</a> 
<a name=L218 href="source/boot/setup.s#L218">218</a> idt_48:
<a name=L219 href="source/boot/setup.s#L219">219</a>         .word   0                       ! idt limit=0
<a name=L220 href="source/boot/setup.s#L220">220</a>         .word   0,0                     ! idt base=0L
<a name=L221 href="source/boot/setup.s#L221">221</a> 
<a name=L222 href="source/boot/setup.s#L222">222</a> gdt_48:
<a name=L223 href="source/boot/setup.s#L223">223</a>         .word   0x800           ! gdt limit=2048, 256 GDT entries
<a name=L224 href="source/boot/setup.s#L224">224</a>         .word   512+gdt,0x9     ! gdt base = 0X9xxxx
<a name=L225 href="source/boot/setup.s#L225">225</a>         
<a name=L226 href="source/boot/setup.s#L226">226</a> .text
<a name=L227 href="source/boot/setup.s#L227">227</a> endtext:
<a name=L228 href="source/boot/setup.s#L228">228</a> .data
<a name=L229 href="source/boot/setup.s#L229">229</a> enddata:
<a name=L230 href="source/boot/setup.s#L230">230</a> .bss
<a name=L231 href="source/boot/setup.s#L231">231</a> endbss:
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