AM625: PRU SPI Settings

Hello John,

We have some PRU sample code for implementing the SPI protocol by bitbanging the PRU cores, but I am not sure if there is any sample code for the PRU controlling the SPI peripheral. Let me ask around.

I am not an RTOS developer, so I am not going to be able to answer exactly how the M4F driver for SPI is written. It is possible that the data structure you are looking at contains values that are used for multiple different registers, or values that are used by functions and not actually programmed into the SPI registers. Your best bet is to read through the driver functions themselves to see how the data structure is being used.

You will probably want to take a look at the AM62x Technical Reference Manual (TRM) section Peripherals > MCSPI > MCSPI programming guide to double-check your register reads and writes in your PRU code, and to make sure that the information you are reading in the M4F driver makes sense.

Regards,

Nick

Hi Nick / PRU expert team:

I need your help. I was able to use the system spi in PRU and able to transmit data.

I based my code in transmit only mode.

This is my steps (according to the AM62X Technical Reference Manual):

Step 1:

Table 12-58. MCSPI Global Initialization
StepRegister/Bit Field/Programming ModelValue
Perform a software reset.MCSPI_SYSCONFIG[1] SOFTRESET1
Wait until reset is finished?MCSPI_SYSSTATUS[0] RESETDONE=1
Configure static settings (such as SPI controller or
peripheral) as required.MCSPI_MODULCTRL[8-0]0x-
Write MCSPI_SYSCONFIGMCSPI_SYSCONFIG0x-

page: 1166

Step 2:

Table 12-60. MCSPI Transmit Mode Initialization
StepRegister/Bit Field/Programming ModelValue
Set transmit mode for the channel.MCSPI_CHCONF_0/1/2/3[13-12] TRM0x2
Configure SPI clock polarity/phase, clock divider, word MCSPI_CHCONF_0/1/2/3
length, and others for the channel.
Reset the status bits.MCSPI_IRQSTATUS0x0

12.2.3.5.2.1.9.3 Transmit-Only Procedure – Polling Method
Table 12-84 lists the transmit-only procedure using the polling method.
Table 12-84. Transmit-Only Procedure – Polling Method
StepRegister/Bit Field/Programming ModelConfigure the channel according to the mode.See Table 12-60.
Value
Start the channel.MCSPI_CHCTRL_0/1/2/3[0] EN1
Write the transmitter register with data.MCSPI_TX_0/1/2/30x-
Wait until end of transfer?MCSPI_CHSTAT_0/1/2/3[2] EOT=1
Stop the channel.MCSPI_CHCTRL_0/1/2/3[0] EN0

page: 1179

Then, below is the simple code that I created. I was sending a constant data (0x80) but when I tried to capture the MOSI pin via salea the data is incorrect.

//Step 1
	MCSPI0_CFG.SYSCONFIG_bit.SoftReset = 1;
	MCSPI0_CFG.SYSCONFIG_bit.AutoIdle = 1;
	while (MCSPI0_CFG.SYSSTATUS_bit.ResetDone != 1);

	MCSPI0_CFG.MODULCTRL = 0;
	MCSPI0_CFG.SYSCONFIG = 0;
	MCSPI0_CFG.CH0CONF = 0;

	MCSPI0_CFG.CH0CONF_bit.TRM = 2; //Transmit/Receive modes

	MCSPI0_CFG.CH0CONF_bit.PHA = 0; //SPICLK phase
	MCSPI0_CFG.CH0CONF_bit.POL = 0; //SPICLK polarity
	MCSPI0_CFG.CH0CONF_bit.CLKD = 4; //Clock rate 12.5 Mhz
	MCSPI0_CFG.CH0CONF_bit.DPE0 = 1; 
	MCSPI0_CFG.CH0CONF_bit.DPE1 = 0; 
	MCSPI0_CFG.CH0CONF_bit.SPIENSLV = 0;
	MCSPI0_CFG.CH0CONF_bit.WL = 8; //SPI word length

	MCSPI0_CFG.IRQSTATUS = 0;
	MCSPI0_CFG.CH0CTRL_bit.En = 1;

	while (1)
    {
		while (MCSPI0_CFG.CH0STAT_bit.TXFFE != 0);
		MCSPI0_CFG.TX0 = (uint8_t) 128;
		while (MCSPI0_CFG.CH0STAT_bit.EOT != 1);
    }

pinctrl-single,pins = <
            AM62X_IOPAD(0x01bc, PIN_INPUT, 0) /* (A14) SPI0_CLK */
			AM62X_IOPAD(0x01c0, PIN_INPUT, 0) /* (B13) SPI0_D0 - MISO */
			AM62X_IOPAD(0x01c4, PIN_INPUT, 0) /* (B14) SPI0_D1 - MOSI */
			AM62X_IOPAD(0x01b4, PIN_INPUT, 0) /* (A13) SPI0_CS0 */
		>;

I would like to know what am I missing and why I am capturing incorrect data?

Regards,

John

Hello John,

Looks like we do NOT have any internal PRU projects of PRU controlling the on-chip SPI, only projects where the PRU bitbangs the SPI protocol.

I am on vacation today and the rest of the week, so I won't be able to look through your code and settings until next week at the earliest. Please keep in mind you are getting outside the space where I can provide help - I can answer basic questions about PRU development, but once you start getting into the details of custom PRU firmware / system configuration that is beyond what I can help with.

If you are able to narrow the request down to specific questions (i.e., this TRM section on SPI programming sequence is unclear - do I set register A or register B first?), then we will be able to offer more support.

Regards,

Nick

Hi Nick,

In mcu sdk there's a command 'DebugP_log' is there any similar function in PRU software support package that I can call to dump the data in the serial?.

Regards,

John