I am working with a sensor which has a programmable configuration register. After changing this register, I have to reboot the sensor. To do this, I need to temporarily suspend a TWI master driver and manipulate the SCL and SDA GPIO lines directly, as described in this earlier discussion:
Looking through the Nordic documentation, I'm trying to figure out how to get this done.
In the SDK docs I have found the functions nrf_drv_twi_disable() and nrf_drv_twi_enable(). These functions are sparsely documented. Nor are these functions used in any of the software examples. What exactly do they do?
In the hardware docs (Section 47) I found references to the registers PSELSCL and PSELSDA. These registers determine the pins that are driven by the TWI. I found these elements within the NRF_TWI_Type data structure, and I can read their values. The documentation says I can only WRITE these registers when the TWI is disabled.
I started with a pretty simple modification to an existing program; just adding calls to nrf_drv_twi_disable() and nrf_drv_twi_enable() after some data transfers have completed, with short delays in between each call (0.5 seconds each). I haven't tried to modify PSELSCL or PSELSDA yet, or to write to the GPIO lines. Still, this simple change crashes. APP_ERROR_CHECK fails, my program reboots, and then the first new thing that my program tries to do on the TWI (just reading a register) causes another APP_ERROR_CHECK failure.
I don't know that any of this is Nordic's fault, since the slave device is obviously a little strange. But the failure is profound. When my system gets into an error state, I can only solve the problem by completely unplugging everything. I have to turn off my nRF52 board, and disconnect it from USB. I even have to unplug my slave device from the Nordic board (which is also its power source).
After I reboot, provided that a working program is in flash, everything functions again. By "working program" I mean that one which changes the configuration register, but doesn't (yet) perform the sleep-and-wake cycle that I want.
I am using a the nRF52 Preview board and SDK 0.9.2 (the highest revision that I can use).
Thanks for any help you can provide!
