Trying to Compile FreeRtos for Riscv .Error: Instruction csrr requires absolute expression
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Trying to Compile FreeRtos for Riscv .Error: Instruction csrr requires absolute expression
i am trying to compile the FreeRTOS riscv_spike port, with riscv32-unknown-linux-gnu-gcc toolchain but got his error
Error:
../../Source/portable/GCC/RISCV/port.c:121: Error: Instruction csrr requires absolute expression
The following code is from port.c of freeRtos Source
__asm volatile("csrr t0,mtime");
__asm volatile("add t0,t0,%0" :: "r"(configTICK_CLOCK_HZ/configTICK_RATE_HZ));
__asm volatile("csrw mtimecmp,t0");
can anyone describe me what changes i need to make?
i guess the mtime, mtimecmp is invalid
can i add this required definition in "encoding" file by reading the spec?
thanks,
1 Answer
1
As per riscv-privildged-v1.10 in § 3.1.15, mtime & mtimecmp are exposed as a memory-mapped machine-mode register. They are accessed by store (sw) and load instructions (lw), and not by csr* instructions.
sw
lw
csr*
They are therefore platform implementation dependent - in particular their address depend on the platform.
Your code cannot be assembled because the csrr & csrw expect both a value and not a relocatable expression as you have written. But as mentionned at the beginning, you have to use sw and lw instructions - and take care that mtime & mtimecmp are implemented and at which address they can be accessed.
csrr
csrw
I do not know what mtohost and fromhost are. Can you elaborate ?
– Pierre G.
Aug 11 at 6:12
they are also registers like mtime and mtimecmp, i think the same procedure which you mentioned applies for mtohost and fromhost ?You can refer the previous version architecture.Can you give me any example, how i can achieve that using lw and sw instruction?
– aditya
Aug 11 at 6:29
You can have a look at github.com/padmaraob/FreeRTOS-RISCV/blob/master/Source/portable/… which does not need to use __asm to manipulate mtime & mtimecmp (memory mapped reg). Regarding mtohost & fromhost, if they are memory mapped, you just have to do the same.
– Pierre G.
Aug 11 at 6:38
Now understood how i can do it. Do you know when compiling the source it needs encoding.h file, which file in the toolchain, i must copy to the source folder when compiling the Demo source
– aditya
Aug 11 at 7:00
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hi, what about mtohost and fromhost ??
– aditya
Aug 11 at 2:58