How to unblock the CPU during connection intervals with S110 v7.1.0?

[Håkon Alseth]

How do I unblock the CPU with the S110 v7.1.0?

[Håkon Alseth]

Hi,

To disable the CPU blocking with S110 v7.1.0 or newer, you will have to use this API call:

/**@brief Set a BLE option.
 *
 * @details This call allows the application to set the value of an option.
 *
 * @param[in] opt_id Option ID.
 * @param[in] p_opt Pointer to a ble_opt_t structure containing the option value.
 *
 * @retval ::NRF_SUCCESS  Option set successfully.
 * @retval ::NRF_ERROR_INVALID_ADDR Invalid pointer supplied.
 * @retval ::BLE_ERROR_INVALID_CONN_HANDLE Invalid Connection Handle.
 * @retval ::NRF_ERROR_INVALID_PARAM Invalid parameter(s) supplied, check parameter limits and constraints.
 * @retval ::NRF_ERROR_INVALID_STATE Unable to set the parameter at this time.
 * @retval ::NRF_ERROR_BUSY The stack is busy or the previous procedure has not completed.
 */
SVCALL(SD_BLE_OPT_SET, uint32_t, sd_ble_opt_set(uint32_t opt_id, ble_opt_t const *p_opt));

The options available as of now is only one, which is the mutual exclusion of radio activity and CPU usage (read block/unblock CPU in connection interval):

/**@brief Common Option IDs.
 * IDs that uniquely identify a common option.
 */
enum BLE_COMMON_OPTS
{
  BLE_COMMON_OPT_RADIO_CPU_MUTEX = BLE_OPT_BASE    /**< Radio CPU mutex option. @ref ble_common_opt_radio_cpu_mutex_t */
};

And here's a small snippet on how to disable the CPU blocking:

uint32_t opt_id = BLE_COMMON_OPT_RADIO_CPU_MUTEX;
ble_opt_t cpu_blocking_enabled;
cpu_blocking_enabled.common_opt.radio_cpu_mutex.enable = 0;
ble_stack_init();
err_code = sd_ble_opt_set(opt_id, &cpu_blocking_enabled);
/* continue init */

Cheers, Håkon

===============================

Additional images showing how the CPU availability is improved when advertising (same applies when in connection):

Before (CPU blocked during radio active):

After (Concurrent CPU when radio is active):

Black part showing the latency when CPU is blocked. [ADDED]: On the second trace, the CPU is still blocked at some periods because it's the softdevice active and preparing the radio packet, no the radio itself.

Cheers,

Hung Bui

[Jason]

Why nRF51 need to block the CPU to wait for Radio ?

[Jason]

I can not found the "common_opt.radio_cpu_mutex.enable" in SDK 6.1...

[Lucas]

Is it also required that this be on latest hardware revision?

[Lucas]

I attempted this on two chips:

nRF51822-QFAAG0

nRF51822-QFACA1

In both cases I saw performance increases. Similar to what you showed above it isn't perfect. The CPU does block occasionally regardless of if CPU blocking is disabled. I was under the impression that this would only improve performance for hardware revision 3. I guess it works for hardware revision 2 as well? Is this expected behavior?

[Hung Bui]

@Lucas: It's only safe to unblock the CPU on XLR3. On chip version 2 (QFAAG0) there are some PANs that don't allow CPU to be concurrent when the softdevice is active. Please have a look at the release note on S110 v8.0 at Changes section.