Add problems with the PLIC to the journal

JOURNAL.md

@@ -3914,3 +3914,124 @@ frequency is:
 
 Assuming that it actually works well. Let's try that and see if we can have a
 more realistic reading for the CLINT interrupt frequency.
+
+Something is going on with the plictool:
+
+    ~ # plictool
+    plic=0x40800000 nsources=1024 ncontexts=15872
+    src=1 pend=1 prio=1 ctx=1 thre=0 <--- zero
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+    src=33 pend=0 prio=0 ctx=1 thre=2
+    ~ # plictool
+    plic=0x40800000 nsources=1024 ncontexts=15872
+    src=1 pend=1 prio=1 ctx=1 thre=2 <--- now changed to 2???
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+    src=33 pend=0 prio=0 ctx=1 thre=2
+
+Either the register is changing its value on its own, or the tool is causing it.
+
+Let's revert the threshold to 0, but writing to the threshold address, should be
+at 0x40a01000.
+
+    ~ # devmem 0x40a01000
+    0x00000002
+    ~ # devmem 0x40a01000
+    0x00000002
+    ~ # devmem 0x40a01000
+    0x00000002
+    ~ # devmem 0x40a01000 8 0
+    ~ # devmem 0x40a01000
+    0x00000000
+    ~ # devmem 0x40a01000
+    0x00000000
+    ~ # devmem 0x40a01000
+    0x00000000
+    ~ # plictool -c 2 -s 5 <-- limiting the sources and contexts
+    plic=0x40800000 nsources=5 ncontexts=2
+    src=1 pend=1 prio=1 ctx=1 thre=0 <-- good
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+    ~ # plictool -c 2 -s 5
+    plic=0x40800000 nsources=5 ncontexts=2
+    src=1 pend=1 prio=1 ctx=1 thre=0
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+    ~ # plictool -c 2 -s 5
+    plic=0x40800000 nsources=5 ncontexts=2
+    src=1 pend=1 prio=1 ctx=1 thre=0 <--- stable
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+    ~ # cat /proc/interrupts
+                CPU0
+       1:          1  SiFive PLIC   1 Edge      ttyS1
+       5:     195413  RISC-V INTC   5 Edge      riscv-timer
+    ~ # cat /proc/int^Crupts
+
+    ~ # echo a > /dev/ttyS1
+    ~ # cat /proc/interrupts
+                CPU0
+       1:          1  SiFive PLIC   1 Edge      ttyS1
+       5:     197102  RISC-V INTC   5 Edge      riscv-timer
+    ~ # plictool -c 2 -s 5
+    plic=0x40800000 nsources=5 ncontexts=2
+    src=1 pend=1 <--- wtf prio=1 ctx=1 thre=0
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+    ~ # devmem 0x40a01004
+    0x00000000 <--- the claim register continues to give 0 instead of 1
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004 8 5 <-- try writing 5
+    ~ # devmem 0x40a01004
+    0x00000000 <--- no change
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004 8 1 <-- try with 1
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # devmem 0x40a01004
+    0x00000000
+    ~ # plictool -c 2 -s 5
+    plic=0x40800000 nsources=5 ncontexts=2
+    src=1 pend=0 <--- now it is gone prio=1 ctx=1 thre=0
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+    ~ # cat /proc/interrupts
+                CPU0
+       1:          3 <-- and we have >1  SiFive PLIC   1 Edge      ttyS1
+       5:     213775  RISC-V INTC   5 Edge      riscv-timer
+    ~ # echo a > /dev/ttyS1
+    ~ # cat /proc/interrupts
+                CPU0
+       1:          3 <--- stuck again SiFive PLIC   1 Edge      ttyS1
+       5:     214551  RISC-V INTC   5 Edge      riscv-timer
+    ~ # plictool -c 2 -s 5
+    plic=0x40800000 nsources=5 ncontexts=2
+    src=1 pend=1 prio=1 ctx=1 thre=1 <--- again set to 1
+    src=2 pend=0 prio=1
+    src=3 pend=0 prio=1
+    src=4 pend=1 prio=1
+
+Clearly something is not working well in the PLIC.
+