On Thu, Mar 15, 2018 at 11:29 AM, Sebastian Huber <
sebastian.hu...@embedded-brains.de> wrote:
>
>
> On 15/03/18 05:56, Udit agarwal wrote:
>
>> c/src/lib/libbsp/arm/atsam/startup/getentropy-trng.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/c/src/lib/libbsp/arm/atsam/startup/getentropy-trng.c
>> b/c/src/lib/libbsp/arm/atsam/startup/getentropy-trng.c
>> index 11e24dc..b26b6a8 100644
>> --- a/c/src/lib/libbsp/arm/atsam/startup/getentropy-trng.c
>> +++ b/c/src/lib/libbsp/arm/atsam/startup/getentropy-trng.c
>> @@ -17,6 +17,8 @@
>> #include <string.h>
>> #include <rtems/sysinit.h>
>>
>> +static rtems_mutex atsam_trng_reg = RTEMS_MUTEX_INITIALIZER("atsam
>> _trng_reg");
>>
>
> Is this a register or a mutex?
>
> +
>> static void atsam_trng_enable(void)
>> {
>> PMC_EnablePeripheral(ID_TRNG);
>> @@ -29,9 +31,12 @@ int getentropy(void *ptr, size_t n)
>> uint32_t random;
>> size_t copy;
>>
>> + rtems_mutex_lock(&atsam_trng_reg);
>> while ((TRNG_GetStatus() & TRNG_ISR_DATRDY) == 0) {
>> /* wait */
>> }
>> +
>> + rtems_mutex_unlock(&atsam_trng_reg);
>>
>
> Now the status register read is protected by a mutex.
>
> random = TRNG_GetRandData();
>>
>
> Can you ensure that this read is correct in a multi-threaded application
> (the status register has the right value during the read)?
>
> Oh yes, i think i misinterpreted your previous suggestion of surrounding
the while loop by mutex, it should be the outer while loop. some thing like
this?:
while (n > 0) {
uint32_t random;
size_t copy;
rtems_mutex_lock(&atsam_trng_mutex);
while ((TRNG_GetStatus() & TRNG_ISR_DATRDY) == 0) {
/* wait */
}
random = TRNG_GetRandData();
/*
* Read TRNG status one more time to avoid race condition.
* Otherwise we can read (and clear) an old ready status but get
* a new value. The ready status for this value wouldn't be
* reset.
*/
TRNG_GetStatus();
copy = sizeof(random);
if (n < copy ) {
copy = n;
}
memcpy(ptr, &random, copy);
n -= copy;
ptr += copy;
rtems_mutex_unlock(&atsam_trng_mutex);
}
>
>> /*
>> @@ -51,6 +56,7 @@ int getentropy(void *ptr, size_t n)
>> ptr += copy;
>> }
>>
>> + rtems_mutex_destroy(&atsam_trng_reg);
>>
>
> Here you destroy the mutex. What happens if you call getentropy() a
> second time?
> return 0;
>> }
>>
>
> --
> Sebastian Huber, embedded brains GmbH
>
> Address : Dornierstr. 4, D-82178 Puchheim, Germany
> Phone : +49 89 189 47 41-16
> Fax : +49 89 189 47 41-09
> E-Mail : sebastian.hu...@embedded-brains.de
> PGP : Public key available on request.
>
> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
>
>
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