SPI bus

[aicastell]

Hello forum.

I'm trying to run some simple tests with a slave sensor connected on the SPI bus with a master Jennic JN5148 micro controller. Master and slave are connected using VCC, GND, MISO, CS and CLK pins of the J4 connector .

I think the common API to use for all the platforms at userspace level is the one implemented at contiki-jn51xx/core/dev/spi.h, that is:

SPI_WRITE(data)
SPI_WRITE_FAST(data)
SPI_READ(data)
SPI_FLUSH()

Is that true?

Also, I found some spi.c files for the cpu/msp430 and cpu/avr CPU's. But there isn't any equivalent file for the cpu/jennic. Comparing msp430 and avr source files, both declare a "spi_init" function that initialize the SPI bus. But I'm not sure if that initialization is also needed for the JN5148, or maybe not. If needed, this is a complex stuff to implement it by myself without any help. Does some of you have this initialization function for the JN5148, or can give some advice to try to implement it by myself?

Thank you in advance!!.

Best regards,
-- Ivan

[aicastell]

Ok, I made some progress on this issue. On JN5148 uC datasheet, I found this uC has a ROM API for interfacing with on-chip peripherals. This API is documented at "JN-RM-2001-Integrated-Peripherals-API-3v1.pdf" document. After some reading, I now understand I2C driver on this uC is also implemented using this ROM API. So, the problem simplifies to just writing a SPI driver using that ROM API, such as done on i2c driver. At least, I can focus my effort in the right direction now. I'll try to implement that driver and I share it with Jennisense community, hope to be able!! :)

[aicastell]

My SPI sensor is a MAX6675 temperature sensor (SPI bus slave), connected to JN5148 (SPI bus master) according to this diagram:

Jennic JN5148 (Master)
Expansion Connector J4      Sensor (Slave)
pin3        DIO2            CS
pin22       SLCK            SCK
pin23       MISO            SO
pin39       VCC             VCC
pin40       GND             GND

MAX6675 datasheet explains this sensor works sending two data bytes to master device, when master selects that sensor with the chip (CS). But I always receive two wrong bytes (MSB=0xFF and LSB=0xFF).

I have some questions related with the source code (attached at the end) and with Jennic documentation:

1. It is supposed that first parameter of vAHI_SpiConfigure (u8SlaveEnable) is the number of extra SPI slaves to control (from 0 to 4). Documentation is really confusing at this point. I understand u8SlaveEnable enables a bitmask as explained below:

u8SlaveEnable  |                 enabled CS mask
---------------+-----------------------------------------------
               |                  DIO3 DIO2 DIO1 DIO0 FLASH-MEM
0              |   0    0    0    0    0    0    0    1
1              |   0    0    0    0    0    0    1    1
2              |   0    0    0    0    0    1    1    1
3              |   0    0    0    0    1    1    1    1
4              |   0    0    0    1    1    1    1    1

So, I use u8SlaveEnable=3 to enable a bitmask with DIO2 enabled on it. Is this correct or wrong?

2. According to vAHI_SpiSelect documentation (page 218 of Integrated Peripherals API), the slave-select lines are asserted immediately if “automatic slave selection” is disabled. As you can see, sixth parameter of vAHI_SpiConfigure is false (bAutoSlaveSelect=false). So, after calling vAHI_SpiSelect(DIO2) the Chip Select signal should be automatically enabled. I don't have an oscilloscope to check it.

3. I never call vAHI_SpiStartTransfer because SPI master has to send anything to the slave, just receive 2 bytes after enabling CS (at least, that's what I understood).

I'm sure I'm wrong in some of the 3 assumptions, but after reading documentation several times, I can't see the problem.

Hope some of you with experience on the Jennic can help.
Thanks a lot in advance!

Here is the driver source code:

#define DIO0 0x1
#define DIO1 0x2
#define DIO2 0x4
#define DIO3 0x8

void
max6675_initialize (void)
{
    u32AHI_Init();

    vAHI_SpiConfigure(
            4, // number of extra SPI slaves to control (0 to 4)
            E_AHI_SPIM_MSB_FIRST, // MSB bit first
            0,0, // data latched on rising edge of clock
            8, // clock divisor, 16MHz / 2*n MHz = 1MHz
            E_AHI_SPIM_INT_DISABLE, // don't generate interrupt when transfer completed
            E_AHI_SPIM_AUTOSLAVE_DSABL); // disable auto CS
}

uint16_t
max6675_read()
{
    uint16_t data = 0;

    // CS low
    vAHI_SpiWaitBusy();
    vAHI_SpiSelect(DIO2);
    //vAHI_SpiStartTransfer(15, 1);
    vAHI_SpiWaitBusy();

    // read SPI bus (16 bits)
    data = u16AHI_SpiReadTransfer16();

    // CS high
    vAHI_SpiWaitBusy();
    vAHI_SpiSelect(0); // Stop();
    vAHI_SpiWaitBusy();

    return data;
}

[aicastell]

Hello forum.

After some trial and error , I finally solved my issue. The question was using "vAHI_SpiStartTransfer" in the proper way. To fix the issue I used this call:

vAHI_SpiStartTransfer(15, 1);

That instruction seems to generate 16 CLK pulses to be able to receive 16 bits from slave. That fixed my issue, and my sensor is providing MSB and LSB as expected now.

I want to share my driver with all of you, hope it can be helpful for somebody else:

$ cat max6675-sensor.h
#ifndef MAX6675_H
#define MAX6675_H

#define J4_PIN1 0x2 // DIO1
#define J4_PIN2 0x4 // DIO2
#define J4_PIN3 0x8 // DIO3

static uint8_t gCS; // Global ChipSelect

void max6675_initialize (uint8_t);
uint16_t max6675_read ();

#endif

$ cat max6675-sensor.c

/ * Author(s): Angel Ivan Castell Rovira al004140@gmail.com */
#include "max6675-sensor.h"
#include "AppHardwareApi.h"

void
max6675_initialize (uint8_t chipselect)
{
/* Initialite the API */
uint32_t version = u32AHI_Init();

/* init SPI bus */

vAHI_SpiConfigure(
        4, // number of extra SPI slaves to control (0 to 4)
        E_AHI_SPIM_MSB_FIRST, // MSB bit first
        0,0, // data latched on rising edge of clock (00, 01, 10, 11?)
        16, // clock divisor, 16MHz / 2*n MHz = 500KHz
        E_AHI_SPIM_INT_DISABLE, // don't IRQ when transfer completed

        E_AHI_SPIM_AUTOSLAVE_DSABL); // disable auto CS

gCS = chipselect;

}

uint16_t
max6675_read()
{
uint16_t rawdata = 0;

// CS low
vAHI_SpiWaitBusy();
vAHI_SpiSelect(gCS);
// Values are written to disconnected MOSI signal,
// BUT this instruction seems to enable 16 CLK pulses to receive data!!

vAHI_SpiStartTransfer(15, 1);
vAHI_SpiWaitBusy();

// read SPI bus (16 bits)
rawdata = u16AHI_SpiReadTransfer16();
// rawdata contains now 2 bytes, first byte in MSB

// CS high
vAHI_SpiWaitBusy();
vAHI_SpiStop(); // vAHI_SpiSelect(0);
vAHI_SpiWaitBusy();

return rawdata;

}