SPI slave mode switching LPC4370

Gaico — Sun, 20 Nov 2022 12:39:02 GMT

Hello,

I would like to ask for some help finding out how to switch SPI mode during runtime on the LPC4370. I have considered this post made on a similar issue to what I am experiencing but this does not line up with my possibilities using the LPC. This might be very simple but I appear to be rather stuck in this.

Issue

I am using SSP1, and have three slaves connected to it. Each slave functions on a different SPI mode. During initialization, I successfully communicate with all three:

1. Slave 0 --> SPI mode 1

2. Slave 1 --> SPI mode 0

3. Slave 2 --> SPI mode 3

But after the initialization of slave 2, I need the following functionality inside of an infinite loop:

1. Communicate with Slave 1 (SPI mode 0)

2. Communicate with slave 2 (SPI mode 3)

3. Return to step 1 and repeat

(Slave 0 is not communicated with anymore).

What I am seeing is that after the initiation of Slave 2, if I want to communicate with slave 1, the SPI mode is stuck to SPI mode 3 (which is expected as I am using a pointer to the SSP base, see code). But when using a Logic Analyser, I am seeing behaviour that is more akin to a different SPI mode (I'd expect to see slave 1 communicate in SPI mode 3):

*Setting*	Slave 2	Slave 1	Result comm. Slave 1 after init. Slave 2
Mode	Mode 3	Mode 0	Mode 2
CPOL	1	0	1
CPHA	1	0	0

*Setting*	Slave 2	Slave 1	Result comm. Slave 1 after init. Slave 2
Mode	Mode 1	Mode 0	Mode 1
CPOL	0	0	0
CPHA	1	0	1

Wanted situation

I need to switch the SPI mode rapidly during runtime to interface with two of the slaves:

Setup:

Initialize slave 1 in SPI mode 0
Initialize slave 2 in SPI mode 3

Infinite loop:

Switch SPI mode to 0 (slave 1)
Slave 1 (SPI mode 0) --> communicate measurement
Switch SPI mode to 3 (slave 2)
Slave 2 --> communicate measurement
Go back to step 1 inside of the loop

Code used

#define LPC_SSP LPC_SSP1

/* Slave 1 initialization */ void SL1_init() { (var 'ports' init) Chip_SSP_Disable(LPC_SSP); SL1_Init(LPC_SSP, ports, TDC_clock_freq); } void SL1_Init(LPC_SSP_T* SPI_BUS, SL_ports config, float Clock_frequency) { Slave1_SPI = SPI_BUS; //global var inside of this file SL1_Init_SPI(); // init ports Clock_Frequency = Clock_frequency; } void SL1_Init_SPI() { Chip_SSP_Init(Slave1_SPI); SSP_ConfigFormat ssp_format; ssp_format.frameFormat = SSP_FRAMEFORMAT_SPI; ssp_format.bits = SSP_DATA_BITS; ssp_format.clockMode = SSP_CLOCK_MODE0; Chip_SSP_SetFormat(Slave1_SPI, ssp_format.bits, ssp_format.frameFormat, ssp_format.clockMode); Chip_SSP_SetMaster(Slave1_SPI, 1); Chip_SSP_SetBitRate(Slave1_SPI, 10000000); Chip_SSP_Enable(Slave1_SPI); }

For slave 2:

void Init_Slave2(LPC_SSP_T* spi_bus, Slave2_con config) { Slave2_SPI = spi_bus; Slave2_Init_SPI(); //pin init } void Slave2_Init_SPI() { // Chip_SSP_Disable(Slave2_SPI);//new Chip_SSP_Init(Slave2_SPI); SSP_ConfigFormat ssp_format; ssp_format.frameFormat = SSP_FRAMEFORMAT_SPI; ssp_format.bits = SSP_DATA_BITS; ssp_format.clockMode = SSP_CLOCK_MODE3; //can be 1 or 3 Chip_SSP_SetFormat(Slave2_SPI, ssp_format.bits, ssp_format.frameFormat, ssp_format.clockMode); Chip_SSP_SetMaster(Slave2_SPI, 1); Chip_SSP_SetBitRate(Slave2_SPI, 1000000); Chip_SSP_Enable(Slave2_SPI); }

Things tried already

Both slaves are changing the pointer directly to LPC_SSP. Which I think is needed? I thought I could 'just' recall the slavex_init_spi() function during runtime, but this resulted in the LPC_SSP C0 register being completely messed up:

Initiation

Measurement loop

Slave 1 as defined before Slave 2

Slave 2 defined

Slave 1 communication (firstly calling the slave1_init_SPI function)

Hex:0xa07

Binary:101000000111

Hex:0x65c7

Binary:110010111000111

Hex:0xfe87

Binary:1111111010000111

Considerations

Do I need to add a forced delay between the re-initiation of the SPI before or after I'm trying to communicate?

I cannot plainly use different SSP ports as the controller is connected to a custom PCB (which has worked before but I do not possess that code).

Thank you for your consideration and take care!

Re: SPI slave mode switching LPC4370

Gaico — Mon, 21 Nov 2022 09:17:22 GMT

The issue was that the

Chip_SSP_Disable(LPC_SSP);

Was not inside of init SPI function. So the SPI was never turned off. Adding this inside of the function made everything work fine.