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fix 10-SystemCall trap bug #15

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fix 10-SystemCall trap bug #15

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ccckmit
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@ccckmit ccckmit commented Nov 15, 2021

  1. timer_scratch[][] => trap_scratch[][]
  2. 擴大 scratch 大小為 32+1
  3. 用 csrrw t6, mscratch, t6 , 避免原本 t6 可能改變的風險

ianchen0119
ianchen0119 reviewed Nov 19, 2021
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相關 comment 都在 sys.s，再麻煩老師解惑 <(_ _)>

10-SystemCall/src/sys.s

# save mepc to context of current task
csrr a0, mepc
sw a0, 124(t6)
sw a0, 128(t6)
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124(t6) 應該沒有使用到，為何要用 128(t6) 呢

10-SystemCall/src/sys.s

csrrw t6, mscratch, t6
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感覺這行與 line 162 的 csrrw t6, mscratch, t6 都可以移除掉(?)

10-SystemCall/src/sys.s

# Do actual context switching.
# Notice this will enable global interrupt
csrrw t6, mscratch, t6
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t 開頭的暫存器都是提供暫存用的，trap_vector 結束時不換回來也沒關係。

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@ccckmit @ianchen0119