TMS320F28386S: SPI and CM-SSI behaviour is the same. Phase issue.

Part Number: TMS320F28386S

Tool/software:

Currently I have 5 SPI devices connected to MCU:

• 2xADS8900B ADCs
• AD5293 digital potenziometer
• FM25V02A FRAM storage
• BT815 based display module connected to CM's SSI.

All of these have the same issue:

According to datasheets, all the devices operate with SPI mode 0 (CPOL=0, CPHA=0) except AD5293, which is a mode 1 (CPOL=0, CPHA=1) device.

So, when I do configure SPI ports to these settings, nothing works, except for BT815, at least it accepts data sent.

So I change the settings for SPI port to the opposite, mode 0 for AD5293 and mode 1 for others. After this all the device accept the commands. But:

When I read data back from devices it is shifted 1 bit! AD5293 is ok, as no reading from it is required.

So for BT815 I change SSI port to mode 1 before reading and to mode 0 back after.

For other 3 devices on SPI ports I change SPI port to mode 0 before reading and to mode 1 back after.

So common workflow for all SPI devices except AD5293 is:

(port is initally configured for mode 1, no matter the devices are mode 0)

1. Send command
2. Change to mode 0
3. Read response
4. Change to mode 1

Now everything works fine. But it is weird!

The code which works for FRAM is:

static void SPI_setReadMode(bool read)
{
    SPI_disableModule(FRAM_SPI_BASE);
    SPI_setConfig(FRAM_SPI_BASE, DEVICE_LSPCLK_FREQ, read ? SPI_PROT_POL0PHA0 : SPI_PROT_POL0PHA1,
                  SPI_MODE_CONTROLLER, FRAM_SPI_BITRATE, FRAM_SPI_DATAWIDTH);
    SPI_setPTESignalPolarity(FRAM_SPI_BASE, SPI_PTE_ACTIVE_LOW);
    SPI_enableModule(FRAM_SPI_BASE);

}

void FRAM_Read(uint32_t addr, void *buf, uint32_t len) {
    FRAM_CS_LOW();
    SPI_WriteByte(FRAM_SPI_HANDLE, 0x03); // READ
    SPI_WriteByte(FRAM_SPI_HANDLE, (addr >> 8) & 0xFF);
    SPI_WriteByte(FRAM_SPI_HANDLE, addr & 0xFF);
    uint8_t *p = (uint8_t*)buf;
    uint32_t i;
    SPI_setReadMode(true);
    for (i = 0; i < len; i += 2)
    {
        uint8_t w = SPI_ReadByte(FRAM_SPI_HANDLE);
        p[i / 2] = w << 8;
        w = SPI_ReadByte(FRAM_SPI_HANDLE);
        p[i / 2] |= w;
    }
    while (SPI_isBusy(FRAM_SPI_HANDLE));
    FRAM_CS_HIGH();
    SPI_setReadMode(false);
}

And for BT815 on CM:

void HAL_SPI_ReadBuffer(uint8_t *Buffer, uint32_t Length)
{
    HAL_SPI_Write(0);
    SSI_disableModule(SSI0_BASE);
    SSI_setConfig(SSI0_BASE, CM_CLK_FREQ, SSI_FRF_MOTO_MODE_1, SSI_MODE_MASTER, 12000000, 8);
    SSI_enableModule(SSI0_BASE);
    for(; Length; Buffer++, Length--)
    {
        *Buffer = HAL_SPI_Write(0);
    }
    SSI_disableModule(SSI0_BASE);
    SSI_setConfig(SSI0_BASE, CM_CLK_FREQ, SSI_FRF_MOTO_MODE_0, SSI_MODE_MASTER, 12000000, 8);
    SSI_enableModule(SSI0_BASE);
}

The scope shows everething is ok on SPI lines with this code, but 1 bit shifted without.

Changing the bit rate for ports does not affect this behaviour. (The bit rate for FRAM chip is 40MHz by datasheet, I tried reducing it to 400kHz, same result).

I noticed same issue previousely on F2837x devices.

IMPORTANT NOTICE

I will attach the scope shots later, as now I am not at the device, but, Scope shows correct data in mode 0 in BOTH directions for all devices and mode 1 for AD5293.

So the problem is difinitely in SPI/SSI hardware in MCU.