Hello i was wondering if someone could explain what the ^= operator is doing in this c program? The program is being written for an arm architecture.
#include <stdint.h>
#include <pru_cfg.h>
volatile register uint32_t __R30;
volatile register uint32_t __R31;
void main() {
volatile uint32_t gpo;
/* Clear GPO pins */
gpo = (__R30 & 0xFFFF0000);
__R30 = gpo;
while(1) {
gpo = __R30;
gpo ^= 0xF;
__R30 = gpo;
__delay_cycles(100000000); // half-second delay
}
}
If you require any other info, let me know, Thank you
In C, ^ is the bitwise exclusive or, and
gpo ^= 0xF;
is equivalent to
gpo = gpo ^ 0xF;
See https://en.cppreference.com/w/c/language/operator_assignment#Compound_assignment for more details about it.
Related
I'm working on Keil software and using LM3S316 microcontroller. Usually we address registers in microcontrollers in form of:
#define GPIO_PORTC_DATA_R (*((volatile uint32_t *)0x400063FC))
My question is how can I access to single pin of register for example, if I have this method:
char process_key(int a)
{ PC_0 = a ;}
How can I get PC_0 and how to define it?
Thank you
Given say:
#define PIN0 (1u<<0)
#define PIN1 (1u<<1)
#define PIN2 (1u<<2)
// etc...
Then:
char process_key(int a)
{
if( a != 0 )
{
// Set bit
GPIO_PORTC_DATA_R |= PIN0 ;
}
else
{
// Clear bit
GPIO_PORTC_DATA_R &= ~PIN0 ;
}
}
A generalisation of this idiomatic technique is presented at How do you set, clear, and toggle a single bit?
However the read-modify-write implied by |= / &= can be problematic if the register might be accessed in different thread/interrupt contexts, as well as adding a possibly undesirable overhead. Cortex-M3/4 parts have a feature known as bit-banding that allows individual bits to be addressed directly and atomically. Given:
volatile uint32_t* getBitBandAddress( volatile const void* address, int bit )
{
__IO uint32_t* bit_address = 0;
uint32_t addr = reinterpret_cast<uint32_t>(address);
// This bit maniplation makes the function valid for RAM
// and Peripheral bitband regions
uint32_t word_band_base = addr & 0xf0000000u;
uint32_t bit_band_base = word_band_base | 0x02000000u;
uint32_t offset = addr - word_band_base;
// Calculate bit band address
bit_address = reinterpret_cast<__IO uint32_t*>(bit_band_base + (offset * 32u) + (static_cast<uint32_t>(bit) * 4u));
return bit_address ;
}
Then you can have:
char process_key(int a)
{
static volatile uint32_t* PC0_BB_ADDR = getBitBandAddress( &GPIO_PORTC_DATA_R, 0 ) ;
*PC0_BB_ADDR = a ;
}
You could of course determine and hard-code the bit-band address; for example:
#define PC0 (*((volatile uint32_t *)0x420C7F88u))
Then:
char process_key(int a)
{
PC0 = a ;
}
Details of the bit-band address calculation can be found ARM Cortex-M Technical Reference Manual, and there is an on-line calculator here.
I was looking into spi driver in u boot , here is a small snippet from
omap_spi.c
void spi_init(void)
{
gpMCSPIRegs = (MCSPI_REGS *)MCSPI_SPI1_IO_BASE;
unsigned long u, n;
/* initialize the multipad and interface clock */
spi_init_spi1();
/* soft reset */
CSP_BITFINS(gpMCSPIRegs->SYSCONFIG, SPI_SYSCONFIG_SOFTRESET, 1);
for (n = 0; n < 100; n++) {
u = CSP_BITFEXT(gpMCSPIRegs->SYSSTATUS,
SPI_SYSSTATUS_RESETDONE);
if (u)
break;
}
...more code
}
here in
omap_spi.h
#define CSP_BITFINS(var, bit, val) \
(CSP_BITFCLR(var, bit)); (var |= CSP_BITFVAL(bit, val))
my confusion here is that when they do soft reset , they call this CSP_BITFINS macro. inside this macro all they do is just manipulate bits and fill structures. where do they access that hardware registers to configure ?
If you look further, you'll find that the pointer they are using, gpMCSPIRregs, is volatile and pointing at the memory-mapper hardware registers. The bits they are setting/clearing are in the hardware registers.
Trying to get an ATmega162 USART up and running. This code does exactly what I expect it to:
#define F_CPU 14745600UL
#define UBRR_1 F_CPU / 16 / 9600 - 1
#define UBRR_2 F_CPU / 16 / 31250 - 1
#include <inttypes.h>
#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/delay.h>
int main(){
uint16_t ubrr1 = UBRR_1;
UBRR0H = (uint8_t)(ubrr1 >> 8);
UBRR0L = (uint8_t)ubrr1;
UCSR0B = _BV(TXEN0);
UCSR0C = _BV(URSEL0) | _BV(UCSZ00) | _BV(UCSZ01);
uint16_t ubrr2 = UBRR_2;
UBRR1H = (uint8_t)(ubrr2 >> 8);
UBRR1L = (uint8_t)ubrr2;
UCSR1B = _BV(RXEN1);
UCSR1C = _BV(URSEL1) | _BV(UCSZ10) | _BV(UCSZ11);
DDRB = _BV(PB0) | _BV(PB1);
PORTB |= _BV(PB0);
while (1){
PORTB ^= _BV(PB0);
_delay_ms(50);
// byte received on usart 1
if ((UCSR1A & _BV(RXC1)) != 0){
// usart 0 ready to write
if ((UCSR0A & _BV(UDRE0)) != 0){
uint8_t b = UDR1;
UDR0 = b;
}
}
}
return 0;
}
That is, initializes the two USARTs at different baud rates, reads from USART1 and writes to USART0. Works great. Yes, I know that _delay_ms() is messing with the timing, but it works fine for this example. Now, as soon as I enable the RX interrupt on USART1 and add the appropriate vector, the main loop stops running (the LED isn't blinking, at least):
#define F_CPU 14745600UL
#define UBRR_1 F_CPU / 16 / 9600 - 1
#define UBRR_2 F_CPU / 16 / 31250 - 1
#include <inttypes.h>
#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/delay.h>
int main(){
uint16_t ubrr1 = UBRR_1;
UBRR0H = (uint8_t)(ubrr1 >> 8);
UBRR0L = (uint8_t)ubrr1;
UCSR0B = _BV(TXEN0);
UCSR0C = _BV(URSEL0) | _BV(UCSZ00) | _BV(UCSZ01);
uint16_t ubrr2 = UBRR_2;
UBRR1H = (uint8_t)(ubrr2 >> 8);
UBRR1L = (uint8_t)ubrr2;
UCSR1B = _BV(RXEN1);
UCSR1C = _BV(URSEL1) | _BV(UCSZ10) | _BV(UCSZ11);
DDRB = _BV(PB0) | _BV(PB1);
// enable usart1 rx interrupt
UCSR1B |= _BV(RXCIE1);
PORTB |= _BV(PB0);
// enable interrupts
sei();
while (1){
PORTB ^= _BV(PB0);
_delay_ms(50);
}
return 0;
}
ISR(USART1_RXC_vect){
uint8_t byte = UDR1;
if ((UCSR0A & _BV(UDRE0)) != 0){
UDR0 = byte;
}
}
The weirdest part is that it's not the sei(); and UCSR1B |= _BV(RXCIE1); lines that make the program stop working -- it's the existence of the ISR. As soon as I comment out that function, the main loop executes normally. Did I miss a flag somewhere?
It's possible this has been caused by the M161C fuse bit (in the extended fuse byte) becoming programmed. This puts the ATmega162 into ATmega161 compatibility mode which causes the device to have a different layout of the interrupt vector table (which the compiler won't know about.) See enter link description here Page 57 for the details. You could test this by compiling with -mmcu=atmega161 and seeing if it fixes the problem.
The other thing which would cause similar behaviour is if this code is run on an (almost identical-looking) ATmega16 instead of an ATmega162 as the UDR1 register is in a different place in the IO register map, meaning that the RXC interrupt flag would never get cleared and the handler would re-enter forever. You can check the register values the compiler is using by disassembling with avr-objdump.
Im making a xor gate in SystemC, from the binding of four NAND gates. I want the module to receive a vector of N bits, where N is passed as parameter. I should be able to perform & and not bitwise operations (for the NAND gate).
The best solution may be using sc_bv_base type, but I don't know how to initialize it in the constructor.
How can I create a bit vector using a custom length?
A way to parameterise the module is to create a new C++ template for the module.
In this example, the width of the input vector can be set at the level of the instantiation of this module
#ifndef MY_XOR_H_
#define MY_XOR_H_
#include <systemc.h>
template<int depth>
struct my_xor: sc_module {
sc_in<bool > clk;
sc_in<sc_uint<depth> > din;
sc_out<bool > dout;
void p1() {
dout.write(xor_reduce(din.read()));
}
SC_CTOR(my_xor) {
SC_METHOD(p1);
sensitive << clk.pos();
}
};
#endif /* MY_XOR_H_ */
Note that the struct my_xor: sc_module is used i.s.o. the SC_MODULE macro. (See page 40 , 5.2.5 SC_MODULE of the IEEE Std 1666-2011).
You can test this with the following testbench:
//------------------------------------------------------------------
// Simple Testbench for xor file
//------------------------------------------------------------------
#include <systemc.h>
#include "my_xor.h"
int sc_main(int argc, char* argv[]) {
const int WIDTH = 8;
sc_signal<sc_uint<WIDTH> > din;
sc_signal<bool> dout;
sc_clock clk("clk", 10, SC_NS, 0.5); // Create a clock signal
my_xor<WIDTH> DUT("my_xor"); // Instantiate Device Under Test
DUT.din(din); // Connect ports
DUT.dout(dout);
DUT.clk(clk);
sc_trace_file *fp; // Create VCD file
fp = sc_create_vcd_trace_file("wave"); // open(fp), create wave.vcd file
fp->set_time_unit(100, SC_PS); // set tracing resolution to ns
sc_trace(fp, clk, "clk"); // Add signals to trace file
sc_trace(fp, din, "din");
sc_trace(fp, dout, "dout");
sc_start(31, SC_NS); // Run simulation
din = 0x00;
sc_start(31, SC_NS); // Run simulation
din = 0x01;
sc_start(31, SC_NS); // Run simulation
din = 0xFF;
sc_start(31, SC_NS); // Run simulation
sc_close_vcd_trace_file(fp); // close(fp)
return 0;
}
Note that I'm using a struct and not a class. A class is also possible.
class my_xor: public sc_module{
public:
The XOR in this code is just the xor_reduce. You can find more about in the IEEE Std 1666-2011 at page 197 (7.2.8 Reduction operators). But I assume this is not the solution you wanted to have.
I have to interface my GSM module with the AM1808 based on ARM9.
I have assigned all the GPIO pins to the Da850.c as well as mux.h files. I successfully created a uImage and inserted that image in my flash.
I need to handle some of that GPIO from User application.
I know that we can handle the GPIO from the Kerel space but i need to handle from the user space.
As for example I have assigned a GPIO for power key to GSM module. I need to change the pin means (HIGH or LOW) through application.
Ok i have written a following code to access it from the User Space,
#include <stdio.h>
#include <time.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <unistd.h>
#include "GSMpwr.h"
#define BS_GSM_PWR_REGISTER 0x01E26014
#define BS_DCDS_MASK 0x00000004
int fd; // Memory device descriptor
unsigned long *pPWR;
unsigned short GetGSMpwr(void)
{
#if defined __HOST_ARM
unsigned long dcd_value = *pPWR;
return (pwr_value >> 7) & 0x01;
#endif
}
void InitializeGSMpwr(void)
{
#if defined __HOST_ARM
int page_size = getpagesize();
unsigned int MAP_addr;
unsigned int reg_addr;
unsigned char *pTemp; // Pointer to GSMpwr register
/*
* Open memory and get pointer to GSMpwr register in the FPGA
*/
if((fd = open("/dev/mem", O_RDWR | O_SYNC)) < 0)
{
printf("failed to open /dev/mem");
return;
}
else
{
MAP_addr = (BS_GSM_PWR_REGISTER & ~(page_size - 1));
pTemp = (unsigned char *)mmap(NULL, page_size,(PROT_READ | PROT_WRITE),MAP_SHARED,fd,MAP_addr);
if((pTemp == MAP_FAILED) || (pTemp == NULL))
{
printf("failed to map /dev/mem");
return;
}
else
{
printf(“Memory Mapped at Address %p. \n”,pTemp);
}
virt_addr = map_base + (control & MAP_MASK);
reg_addr = (BS_GSM_PWR_REGISTER & (page_size - 1));
pPWR = (unsigned long*)(pTemp + reg_addr);
printf("GSM PWR PIN mapped in Application\n");
}
I can only read that pin through this code, Now i want to use that pin as an output and want to go high and low with the time interval of 3sec.
The easiest way is to utilize GPIO support in sysfs, where you could control all the exported GPIO's. Please have a look at the Linux kernel GPIO documentation, in particular, Sysfs Interface for Userspace part.
After you have enabled GPIO support in sysfs (GPIO_SYSFS), the GPIO control would be as easy as:
Example
GPIO=22
cd /sys/class/gpio
ls
echo $GPIO > /sys/class/gpio/export
ls
Notice on the first ls that gpio22 doesn't exist, but does after you export GPIO 22 to user space.
cd /sys/class/gpio/gpio$GPIO
ls
There are files to set the direction and retrieve the current value.
echo "in" > direction
cat value
You can configure the GPIO for output and set the value as well.
echo "out" > direction
echo 1 > value
Example is taken from here.
I got it please find following code for that,I got the Specific pin address and i have accessed that pin like,
unsigned short GetGSMpwr(void)
{
unsigned long pwr_value = *pPWR;
printf("GSM_PWR:check Start : %ld",pwr_value);
return (pwr_value >> 1) & 0x01;
}
unsigned short SetGSMpwr(void)
{
unsigned long pwr_value = *pPWR;
printf("GSM_PWR:check Start : %ld",pwr_value);
*pPWR = ~((pwr_value >> 1) & 0x01);
}
unsigned short ClrGSMpwr(void)
{
unsigned long pwr_value = *pPWR;
printf("GSM_PWR:check Start : %ld",pwr_value);
*pPWR = 256;
}`