MSPM0L1105: SPI0 controller receive interrupt speed

Tool/software:

Hello

We are using the MSPM0L1105 as an SPI peripheral and have configured the pinmux using CCS and sysconfig.

Configuration for SPI is as follows:

We have setup the IRQ handler to perform some very basic benchmarking to test response time:

void PER_SPI_INST_IRQHandler(void)
{
    uint32_t count = 0;
    uint16_t buffer[256] = {0}};

    switch (DL_SPI_getPendingInterrupt(PER_SPI_INST)) { 
        case DL_SPI_IIDX_RX_TIMEOUT:
            loopCount++;
            count =  DL_SPI_drainRXFIFO16(PER_SPI_INST, buffer, 256);
            DL_SPI_transmitDataBlocking16(PER_SPI_INST, loopCount);
            break;

        case DL_SPI_IIDX_RX:
            loopCount++;
            count =  DL_SPI_drainRXFIFO16(PER_SPI_INST, buffer, 256);
            gADCResult = convertAnalogInput(0);
            gADCResult &= 0x0FFF;
            DL_SPI_transmitDataBlocking16(PER_SPI_INST, loopCount);
            break;
        default:
            break;
    }
}

Data being sent is 16bit length per message and a total of 3 messages to represent a real-world messaging for a SPI ADC peripheral.

Command, dummy cycle, response:

There is no issue with receiving all the data and clock cycles:

The issue is I need the RX interrupt to occur between the first and second message to allow me to populate the transmit buffer to respond to the master.

I have tried to set the RX timeout to 125ns in the hope that it would trigger the IRQ in the chip select transition stage (we essentially have 12.5us).

Is there a way to make the SPI IRQ faster so I get notiified when the controller has received 1 message?

Thanks for any assistance.