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chipsalliance / Cores-VeeR-EH1

VeeR EH1 core
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mcontrol chain bit not WARL on triggers 1 & 3 #74

Closed wronkiew-ghs closed 4 years ago

wronkiew-ghs commented 4 years ago

Setting a store address & value breakpoint using chained triggers succeeds in setting and reading back the mcontrol registers if triggers 1 & 2 are used, but the breakpoint is hit on instructions which do not match the second trigger. These are the values read from mcontrol & tdata2 on triggers 1 & 2:

t1 mcontrol 0x2be018c2 t1 tdata2 0xf0040005 t2 mcontrol 0x2be81042 t2 tdata2 0xaaaaaaaa

In my test program the trigger fired on writes to 0xf0040004 which had values other than 0xaaaaaaaa. If I used triggers 0 & 1 instead the data HWBP worked correctly. I also found the chain bit could be set and read back on trigger 3.

The EH1 PRM section on mcontrol notes that attempts to set chain on triggers 1 & 3 are ignored because chaining is only supported on pairs 0/1 and 2/3. RISC-V debug 0.13.2 specifies all tdata registers are WARL so the debugger can determine which features are supported.

This case is likely to come up if a store addr & value HWBP is set after a simple exec HWBP.

tmw-wdc commented 4 years ago

Thank you for reporting this issue. We are looking into it and will report back.

tmw-wdc commented 4 years ago

After some internal discussions, we have decided to fix the issue you have reported. In the next release of the SweRV EH1 core, the chain bit of MCONTROL will have WARL behavior (i.e., the chain bit value will always be '0' for reads of MCONTROL for triggers 1 and 3). Thank you again for reporting this issue. Much appreciated!

wronkiew-ghs commented 4 years ago

Thank you very much for looking into this.