libgloss: riscv: Add support of clock() for semihosting #59
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It's necessary to implement _times() in libsemihosting to add support of clock() function. SYS_ELAPSED and SYS_TICKFREQ semihosting calls are used to get a number of ticks which could be compatible with clock() interface and CLOCKS_PER_SEC value. clock() function from libc must return value which gives us seconds when it's divided by CLOCKS_PER_SEC. By default, CLOCKS_PER_SEC is 10**6 for RISC-V. However, semihosting's tick frequency may differ and usually it's 10**9. Thus, we have to obtain a real value of the tick frequency for the current semihosting setup and calculate a multiplier and use it for adjusting semihosting's number of ticks. E.g., if semihosting's ticks frequency is 10**9 then multiplier is 10**9 / 10**6 = 1000. Signed-off-by: Yuriy Kolerov <kolerov93@gmail.com>
abrodkin
approved these changes
May 12, 2024
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| /* SYS_ELAPSED semihosting call returns a single 64-bit value for 64-bit | ||
| targets and two 32-bit values for 32-bit targets. */ | ||
| #if __riscv_xlen == 32 |
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To make it more future proof, I'd do it like this:
#if __riscv_xlen == 32
...
#elif __riscv_xlen == 64
...
#else
#error "Unexpected bitness."
#endif
| of the tick frequency for the current semihosting setup and | ||
| calculate a multiplier and use it for adjusting semihosting's | ||
| number of ticks. E.g., if semihosting's ticks frequency is 10**9 then | ||
| multiplier is 10**9 / 10**6 = 1000. */ |
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| if (!initialized) | ||
| { | ||
| /* clock() function from libc must return value which gives us seconds |
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typo: ... return a value that when is multiplied by CLOCKS_PER_SEC would result in seconds passed.
| /* SYS_ELAPSED semihosting call returns a number of ticks. */ | ||
| syscall_errno (SEMIHOST_elapsed, data_block); | ||
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| #if __riscv_xlen == 32 |
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It's necessary to implement
_times()in libsemihosting to add support ofclock()function.SYS_ELAPSEDandSYS_TICKFREQsemihosting calls are used to get a number of ticks which could be compatible with clock() interface andCLOCKS_PER_SECvalue.clock()function from libc must return value which gives us seconds when it's divided byCLOCKS_PER_SEC. By default,CLOCKS_PER_SECis10**6for RISC-V. However, semihosting's tick frequency may differ and usually it's10**9. Thus, we have to obtain a real value of the tick frequency for the current semihosting setup and calculate a multiplier and use it for adjusting semihosting's number of ticks. E.g., if semihosting's ticks frequency is10**9then multiplier is10**9 / 10**6 = 1000.Moreover, I found that Picolibc does not adjust
CLOCKS_PER_SECvalue in its semihosting implementation - it uses nakedSYS_ELAPSEDcall for getting value forclock(). Thus,clock() / CLOCKS_PER_SECdoes not return a valid number of seconds.