Hello,
I am working on a custom board based off the MIMXRT1050-EVK demo board using Keilv5 Pro edition. I am currently testing the LPSPI with EDMA and am following the example projects.
My issue is that the LPSPI EDMA is too slow for my project to function correctly. I need to transfer 1280 bits of data using the EDMA to LPSPI transmit buffer at 13Mhz in under 100us. Right now, it is taking about 124us according to my read out.
I set a probe on the LPSPI clock and I notice there is a 300ns delay between every 32 bits sent, shown in the picture below. Why is there a delay every 32 bits? Is there any way I can remove the delay or speed up the EDMA or LPSPI without changing the LPSPI clock frequency?
The function I am using to make the EDMA transfer to LPSPI is LPSPI_MasterTransferEDMA(). In this function is a bunch of LPSPI API calls and configuration. I am currently testing adjusting this function to increase the speed of the transfer or remove the delay between the 32 bits.
I also have another issue where the LPSPI_MasterTransferEDMA() function does not start sending data right way. I am calling this function within an interrupt, it then takes 18us to begin transferring data while still in that same interrupt. I need it to begin immediately. Is there a flag or something that needs to be set to start the EDMA transfer?
My questions:
- Why is there a delay after every 32 bits sent through the LPSPI? Can that be removed?
- Why is the EDMA LPSPI transfer not beginning right away?
Hi,
1) Also can you confirm if this LPSPI on the Cortex M7 can only send 32 bits at a time? Can this be adjusted to send 16 bits?
-- Yes, it will transfer 16-bits in the unit after setting bitsPerFrame is 16, just as the following figure shows.
Have a great day,
TIC
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Hi,
Thanks for your reply.
1) How can I get the LPSPI to transmit data immediately without needing a delay?
-- 1) The steps of modifying the lpspi_edma_b2b_transfer_master demo (SDK library version is 2.8.5)
a) in lpspi_edma_b2b_transfer_master.c, increae the number of tranmit data and transfer baudrate.
#define TRANSFER_SIZE 160U //64U /* Transfer dataSize */
#define TRANSFER_BAUDRATE 15000000U /* Transfer baudrate - 15M */
b) in the LPSPI_MasterGetDefaultConfig() function in the fsl_lpspi.c,
increase the baudRate and bits of per frame, meanwhile, decrease the delay value, below illustrates the modified LPSPI_MasterGetDefaultConfig() function.
void LPSPI_MasterGetDefaultConfig(lpspi_master_config_t *masterConfig)
{
assert(masterConfig != NULL);
/* Initializes the configure structure to zero. */
(void)memset(masterConfig, 0, sizeof(*masterConfig));
masterConfig->baudRate = 15000000;
masterConfig->bitsPerFrame = 32; //8;
masterConfig->cpol = kLPSPI_ClockPolarityActiveHigh;
masterConfig->cpha = kLPSPI_ClockPhaseFirstEdge;
masterConfig->direction = kLPSPI_MsbFirst;
masterConfig->pcsToSckDelayInNanoSec = 1000000000U / masterConfig->baudRate;//masterConfig->baudRate * 2U;
masterConfig->lastSckToPcsDelayInNanoSec = 1000000000U / masterConfig->baudRate;//masterConfig->baudRate * 2U;
masterConfig->betweenTransferDelayInNanoSec = 1000000000U / masterConfig->baudRate;//masterConfig->baudRate * 2U;
masterConfig->whichPcs = kLPSPI_Pcs0;
masterConfig->pcsActiveHighOrLow = kLPSPI_PcsActiveLow;
masterConfig->pinCfg = kLPSPI_SdiInSdoOut;
masterConfig->dataOutConfig = kLpspiDataOutRetained;
}
2) Testing result
After the above modification, the SPI can transfer 160 bytes in 86.3 us which only takes about 1 us longer than the none-delay condition (as Fig 1 shows). And the interval time between per frame is 56 ns (as Fig 2 shows).
In a word, the transmit speed is enough fast for your requirement.
Note: The testing platform is MIMXRT1050.
Fig 1
Fig 2
Have a great day,
TIC
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