Reading a write only register value

RE: Reading a write only register value

Susheel Nuguru — Tue, 08 Aug 2017 11:39:18 GMT

This code looks strange to me and seems that it depends on the undefined behavior. Atleast when using KEIL which reads the registers open in the new constantly, even though writing '1' to any TASKS never shows the register to be '1'. Which implicitly means that this register should always read 0. I do not have the hardware in hand to verify this, but it should be easy to verify this. Pseudocode

volatile uint32_t verify = 0;
NRF_RNG->TASKS_START = 1;
verify = NRF_RNG->TASKS_START;
print verify

RE: Reading a write only register value

Jonathan — Tue, 08 Aug 2017 07:22:50 GMT

In the mynewt RTOS, there's a code that checks if the RNG started in the following manner:

if (NRF_RNG->TASKS_START == 0) {
        NRF_RNG->EVENTS_VALRDY = 0;
        if (g_ble_rng_isr_cb) {
            NRF_RNG->INTENSET = 1;
        }
        NRF_RNG->TASKS_START = 1;
    }

RE: Reading a write only register value

Roger Clark — Mon, 07 Aug 2017 21:32:10 GMT

What code are you talking about ?