nRF52840 BLE causing display glitch on GC9A01 using SPIM

[wyatt_tritium]

We have a product based on the nRF52840 which uses the GC9A01 display driven using SPI on battery power. The device also functions as a Bluetooth connectable so it is normally advertising data at a 1 second interval. If the display is left on for several hours while BLE is enabled, the display will randomly become glitched and stays this way until reset. It appears that the BLE is somehow interfering with SPI and causing corrupt data eventually. We are fairly confident that the issue is not hardware related, as we have eliminated noise using stable power supplies and impedance matching the SPI lines.

Is it possible that the nRF is low on resources and corrupting the SPI data or display buffer when using BLE?

The pin-out for the display is as follows.

• DC - P0.06
• CS - P0.08
• RESET - P0.11
• SDA - P0.12
• SCL - P1.09

We are using nRF Connect SDK v2.5.1.

[Naeem Maroof]

Hi,

There is no known issue like this. 

How much resources your program is using? If there is an overflow then the compilation would tell you about that.

If there is run time issue then you should debug and locate where the problem is occurring.

/br

Naeem

[wyatt_tritium]

Here is the build output. There is no overflow.

Memory region         Used Size  Region Size  %age Used
           FLASH:      953705 B         1 MB     90.95%
             RAM:      145660 B       256 KB     55.56%
        IDT_LIST:          0 GB         2 KB      0.00%

The issue occurs during runtime, but I do not see how to debug it because the issue occurs randomly after several hours to several days.

[Naeem Maroof]

I am not sure what could be the issue.

Are there any logs etc to see if there is any fault reported by the mcu?

Could there be issues with the display itself? like known issues etc?

[hmolesworth]

Simple test: Ensure the RAM areas used by the BLE RADIO and the SPIM are in separate RAM AHB bus masters to see if that improves the performance. We know that SPIM data corruption can occur if the bus master is stalled while attempting to retrieve the next byte from RAM via DMA which can lead to the display commend/data sequence being incorrect. The RADIO has higher priority than the SPIM and will cause a SPIM DMA bus stall on conflict, which may or may not affect the data stream; worse at higher SPIM clock speeds. Here a some brief notes copied from my code (nRF52833, similar to nRF52840); ensuring separate AHB RAM areas is trivial in SDK, not so easy in nRFConnect; please post any results if you get this test to work. The .map file will show whether the RAM areas are indeed separate.

// nRF52833 Bus Masters
// ====================
// Each bus master is connected to all the slave devices using an interconnection matrix. The bus masters are
// assigned priorities, which are used to resolve access when two (or more) bus masters request access to
// the same slave device. When that occurs, the following rules apply:
// - If two (or more) bus masters request access to the same slave device, the master with the highest
// priority is granted the access first.
// - Bus masters with lower priority are stalled until the higher priority master has completed its transaction.
// To avoid AHB bus contention when using multiple bus masters, follow these guidelines:
// - Avoid situations where more than one bus master is accessing the same slave.
// - If more than one bus master is accessing the same slave, make sure that the bus bandwidth is not exhausted.
// Bus Slaves (RAM):
//           Name  AdrSpace    StartAdr    EndAdr      AccType
// Memory =  RAM0  Memory      0x20000000  0x20001FFF  RW
// Memory =  RAM1  Memory      0x20002000  0x20003FFF  RW
// Memory =  RAM2  Memory      0x20004000  0x20005FFF  RW
// Memory =  RAM3  Memory      0x20006000  0x20007FFF  RW
// Memory =  RAM4  Memory      0x20008000  0x20009FFF  RW
// Memory =  RAM5  Memory      0x2000A000  0x2000BFFF  RW
// Memory =  RAM6  Memory      0x2000C000  0x2000DFFF  RW
// Memory =  RAM7  Memory      0x2000E000  0x2000FFFF  RW
// Memory =  RAM8  Memory      0x20010000  0x2001FFFF  RW

[wyatt_tritium]

Thanks for your insight! We're looking into this and will report back. If you have any additional information on how to separate RAM areas in nRF Connect, please let me know.

[hmolesworth]

Should be straightforward, but I see issues and have not bothered yet to try myself; here's a recent ticket where the user is trying to use a specific RAM address, pretty common requirement. noinit-section-at-a-specific-address

Edit: tried __attribute__((at(0x20001000))) but zephyr ignored me:

struct gpio_callback button_cb_data;
C:\ncs>type C:\ncs\v2.7.0\zephyr\samples\basic\button\build\button\zephyr\zephyr.map | find "button_cb_data"
 .bss.button_cb_data
                0x0000000020000288                button_cb_data

struct gpio_callback button_cb_data __attribute__((at(0x20001000)));
C:\ncs>type C:\ncs\v2.7.0\zephyr\samples\basic\button\build\button\zephyr\zephyr.map | find "button_cb_data"
 .bss.button_cb_data
                0x0000000020000288                button_cb_data

[wyatt_tritium]

We have set `NRFX_SPIM3_NRF52840_ANOMALY_198_WORKAROUND_ENABLED` in `nrfx_config_nrf52840.h` to 1 and running tests now. See this note.

https://infocenter.nordicsemi.com/index.jsp?topic=%2Ferrata_nRF52840_Rev2%2FERR%2FnRF52840%2FRev2%2Flatest%2Fanomaly_840_198.html

[hmolesworth]

Didn't know nRFConnect had this workaround; does the map file show that it works? I'm curious what the setting does to the build. I'll try searching for it ..

This is what I found so far in v2.7.0 with Nordic pre-release:

nrfx_config.h
#ifdef CONFIG_NRF52_ANOMALY_198_WORKAROUND
#define NRFX_SPIM3_NRF52840_ANOMALY_198_WORKAROUND_ENABLED 1

nrfx_config_nrf52840.h
 * @brief NRFX_SPIM3_NRF52840_ANOMALY_198_WORKAROUND_ENABLED
#ifndef NRFX_SPIM3_NRF52840_ANOMALY_198_WORKAROUND_ENABLED
#define NRFX_SPIM3_NRF52840_ANOMALY_198_WORKAROUND_ENABLED 0

[wyatt_tritium]

Enabling the workaround does not seem to do anything. The map files are identical before and after enabling this value. Unless I am not enabling the workaround correctly.

Edit: Is this value enabled by default? I looked in the Kconfig and it was already enabled.

CONFIG_NRF52_ANOMALY_198_WORKAROUND

[hmolesworth]

The 198 handler code is here, not sure how it is ensuring buffer placement:

v2.7.0\modules\hal\nordic\nrfx\drivers\src\nrfx_spim.c

No 198 handler here:

v2.7.0\zephyr\drivers\spi\spi_nrfx_spim.c

Wonder just what this code is doing - 0x40000E00 some secret power control register?

// Workaround for nRF52840 anomaly 198: SPIM3 transmit data might be corrupted.

static uint32_t m_anomaly_198_preserved_value;

static void anomaly_198_enable(uint8_t const * p_buffer, size_t buf_len)
{
    m_anomaly_198_preserved_value = *((volatile uint32_t *)0x40000E00);
    if (buf_len == 0)
    {
        return;
    }
    uint32_t buffer_end_addr = ((uint32_t)p_buffer) + buf_len;
    uint32_t block_addr      = ((uint32_t)p_buffer) & ~0x1FFF;
    uint32_t block_flag      = (1UL << ((block_addr >> 13) & 0xFFFF));
    uint32_t occupied_blocks = 0;
    if (block_addr >= 0x20010000)
    {
        occupied_blocks = (1UL << 8);
    }
    else
    {
        do {
            occupied_blocks |= block_flag;
            block_flag <<= 1;
            block_addr  += 0x2000;
        } while ((block_addr < buffer_end_addr) && (block_addr < 0x20012000));
    }
    *((volatile uint32_t *)0x40000E00) = occupied_blocks;
}