PPI will not stop SPIM, however EGU does.

RE: PPI will not stop SPIM, however EGU does.

hmolesworth — Sat, 12 Feb 2022 20:59:15 GMT

Errata 58 for the SPIM when Rx MAXCNT is set to 1 might be worth looking at: An additional byte is clocked out when RXD.MAXCNT = 1

anomaly_832_58

RE: PPI will not stop SPIM, however EGU does.

JosteinBrovold — Sat, 12 Feb 2022 16:45:07 GMT

After more debugging, I figured out that the increased current draw comes from having the RX and TX MAXCNT to 1. Only sending one byte seems to keep the SPI running, resulting in a current draw of about 500 uA.

Increasing RX MAXCNT to 2, allowing it to receive 2 bytes, seems to stop the SPI transaction afterwards, lowering the current draw to about 1 uA.

RE: PPI will not stop SPIM, however EGU does.

JosteinBrovold — Sat, 12 Feb 2022 16:29:18 GMT

I agree that disabling the peripheral should yield the best power consumption. But I am seeing wildly different behavior depending on how much I use the PPI / EGU.

With this code, where the PPI is not used at all. And the stop command is not sent, and the SPIM is not disabled (no writing the ENABLE register). I achieve an average current consumption of 1.33 uA for the whole board. Note that the spim_trigger(STOP) is even commented out, and I get good current consumption. However, while using the PPI, and sending the stop function. I have a total current draw of about 500 uA.

uint32_t ms5803_command(ms5803_command_t command)
{
    transmit_buffer[0] = (uint8_t)command;
    receive_config.max_count = 4;
    spim_set_rx_config(MS5803_SPIM, &receive_config);
    gpio_set_output(MS5803_CS_PIN, 0);
    spim_trigger(MS5803_SPIM, SPIM_TASK_START);
    while(spim_get_event_state(MS5803_SPIM, SPIM_EVENT_END) == 0);
    gpio_set_output(MS5803_CS_PIN, 1);
    spim_reset_event(MS5803_SPIM, SPIM_EVENT_END);
    //spim_trigger(MS5803_SPIM, SPIM_TASK_STOP);
    uint32_t data = 0;
    switch(ms5803_command_length[command])
    {
        case 2: data = (receive_buffer[1] << 8) | (receive_buffer[2]); break;
        case 3: data = (receive_buffer[1] << 16) | (receive_buffer[2] << 8) | (receive_buffer[3]); break;
    }
    return data;
}

RE: PPI will not stop SPIM, however EGU does.

Kenneth — Tue, 08 Feb 2022 08:21:01 GMT

Can you just check that you follow the description for Low power operation in the datasheet?

When putting the system in low power and the peripheral is not needed, lowest possible power consumption is achieved by stopping, and then disabling the peripheral.

The STOP task may not be always needed (the peripheral might already be stopped), but if it is sent, software shall wait until the STOPPED event was received as a response before disabling the peripheral through the ENABLE register.