Description
The objectives of this homework are:
1. Modify vendor-supplied driver code to use a peripheral in an application. This is a realistic scenario.
2. Avoid hard-coding the ports and pins connected to a peripheral.
3. Structure driver and application code into layers, with each layer’s code contained in separate files.
Write a routine that uses SPI to take measurements with the PmodACL accelerometer. These measurements need
not be interrupt-driven. Your code should display readings from the accelerometer on the OLED as follows:
MIN CUR MAX
X sddd sddd sddd
Y sddd sddd sddd
Z sddd sddd sddd
Current values should be read every 10 ms so that the minimum and maximums can be recomputed. However the
display should only be updated every 500 ms. For each reading, s represents a sign (+ or -) and d represents a digit.
The values should be displayed with leading zeroes and signs so that columns stay aligned. The accelerometer’s data
registers contain 10-bit signed values by default, which corresponds to a range of -512 to +511. The sprintf()
function will be useful.
In order to move the PmodACL while the ChipKIT board is stationary, use the twelve-pin extension cable and 12-pin
pin header. Be sure that the cable’s pin marking (it looks like a three-toed footprint) is connected to pin 1 on JE or
JF and pin 1 on the PmodACL.
The accelerometer should function correctly when plugged into either JE or the JF without changing your code. In
other words, your code must auto-sense whether the PmodACL is connected to JE or JF. If the PmodACL is not
connected, the message “ACL not found” should be displayed on the OLED. Be sure to power off your chipKit
board before connecting or disconnecting any peripheral such as the PmodACL.
Like most chip vendors, Analog Devices provides microcontroller driver code for the ADXL345. A version of this
code targets the PIC32:
https://wiki.analog.com/resources/tools-software/uc-drivers/microchip/adxl345
The code resides in GitHub repositories:
https://github.com/analogdevicesinc/no-OS/tree/master/drivers/ADXL345
https://github.com/analogdevicesinc/no-OS/tree/master/Microchip/PIC32MX320F128H/Common
ADXL345.c and ADXL345.h provide an API to configure and use the ADXL345. Communication.c and
Communication.h include SPI and I2C drivers for the ADL345 and a UART driver for a console. You might think
everything has been done for you, but the code does not meet the plug-n-play objective since the SPI channel and pin
assignments are fixed. Review of the SPI code also reveals deficiencies such as:
1. Portability is reduced by the use of hardcoded registers rather than PLIB functions such as SpiChnGetC()
and SpiChnPutC().
2. SPI_Read() will overflow a temporary array and corrupt the stack if bytesNumber > 4.
3. The SPI API does not reflect the fact that SPI performs simultaneous reads and writes.
You should rewrite Communication.c and Communication.h so that:
1. The I2C and UART code is removed.
2. The SPI functions are replaced with:
int SpiMasterInit(int channel)
int SpiMasterIO(char bytes[], int numWriteBytes, int numReadBytes)
2
There is nothing to be gained from retaining any of the old Spi_Init(), Spi_Write(), or Spi_Read() code.
New function interfaces are required, and you need to use PLIB function calls such as SpiChnOpen(),
mPORTxSetPinsDigitalOut(), mPORTxClearBits(), mPORTxSetBits(), SpiChnPutC(), and
SpiChnGetC(). Do not retain busy wait loops or direct writes and reads of PIC32 registers.
If SpiMasterInit()is called with the SPI channel number for connectors JE or JF, the function:
1. Configures the slave select pin on the connector as a digital output.
2. Calls the PLIB function SpiChnOpen() with the appropriate arguments to configure the channel as a SPI
master, with clock polarity and edge options matching the ADXL345, and using byte transfers with enhanced
buffering.
3. Returns a value of 0 to indicate success.
The slave select pin will be manipulated by SpiMasterIO() code since automatic assertion and deassertion of the
slave select pin by the SPI controller can conflict with the ADXL345’s multibyte transfer option. If the
SpiMasterInit() function is not called with the SPI channel number for connectors JE and JF, an error value
(-1) is returned.
The SpiMasterIO() function accepts a bytes array whose first numWriteBytes entries are bytes to be written
from the bytes argument to the slave. The next numReadBytes entries are values to be read from the slave to the
bytes argument. This single API suits handles Figure 37 (SPI 4-Wire Write) and Figure 38 (SPI 4-Wire Read) on
page 16 of the ADXL345 data sheet, and the ADXL345.c code. SPI is inherently full duplex, although for each
transfer either the byte read from the slave or the value written to the slave may be a don’t care (X). A single I/O
function better suits the SPI protocol and avoids code duplication.
The SpiMasterIO() function should return 0 if the SPI channel number is for connector JE or JF; otherwise an
error code (-1) is returned. SpiMasterIO() needs to call PLIB I/O port macros (such as mPORTxClearBits())
to assert the slave select pin before starting the byte transfer, and deassert the slave select pin after finishing the
transfer. The PLIB blocking functions SpiChnPutC() and SpiChnGetC() should be used to write and read bytes.
If you can correctly implement the SpiMasterInit() and SpiMasterIO() functions, then you understand the
SPI protocol.
After revising the SPI layer, the ADXL345 layer should replace the old SPI layer API with the new SPI layer API. This
should be straightforward except for the ADXL345_Init() function, which needs to try communicating with the
ADXL345 over the SPI channels. After calling SpiMasterInit() on a channel, it should attempt to read the
ADXL345’s Device ID register and see if it matches the expected value. This check should be done with the
ADXL345_GetRegisterValue() function and using the constants defined in ADXL345.h. If an ADXL345 is not
connected to the channel, the SDO (slave data out) signal will be floating (undefined). The ADXL345_Init()
function should return the channel number which has the ADXL345 connected, or -1 if an ADXL345 is not detected.
The ADXL345 does not power up in an active state. The ADXL345 datasheet and the main.c code in the following
GitHub repository should help you configure and calibrate the ADXL345:
https://github.com/analogdevicesinc/no-OS/tree/master/Microchip/PIC32MX320F128H/PmodACL
Your requirements may differ from the configuration used by this sample code. Look the #include directives used
in the Analog Devices code to see what is needed when your code is split over several files.
Submit a zipped archive containing your complete source code. A grader should be able to unzip the archive, open
the project, and run it as is. Use this naming convention for the archive that you submit:
__HW6.zip
Replace and by your family name and given name respectively.