Calling ble_nus_string_send() from within a TWI callback (case NRF_DRV_TWI_EVT_DONE) is performing a reset on my PCA10028 (nRF51422). It works fine from the main loop.
Am I right in assuming that BLE operations cannot be issued from such callbacks? But on the other hand, the ble_app_uart example issues the same call within the uart handler (APP_UART_DATA_READY).
I'd appreciate any clarification on the above.
Thanks
Hi,
My guess is that you are trying to execute an interrupt with low priority inside an interrupt routine of high priority. By design, this will lead to a hard fault in the ARM CPU.
Inside ble_nus_string_send() there is a call to sd_ble_gatts_hvx(). All Softdevice calls are implemented as Supervisor Calls (SVC), which is basically a Software interrupt (SWI) with priority level 2* (see the image). By default, the TWI driver configures the TWI interrupt handler with priority level 1*.
When you call ble_nus_string_send() inside your TWI callback you are trying to execute an interrupt with low priority while you are still in the context of an interrupt with a higher priority.
The simple solution is to make sure that the TWI driver is configured with APP_IRQ_PRIORITY_LOW instead of APP_IRQ_PRIORITY_HIGH*. If you look at how the UART is configured in the example you will see that it uses APP_IRQ_PRIORITY_LOW and hence there is no conflict there.
*Notes:
