Global Variable Pointer to array in Sourceboost C

Question

I declared these global variables:

volatile unsigned char BUFFER[7]={0,0,0,0,0,0,0};//to get all data volatile unsigned char *PTR=&BUFFER[0];//points to start address

Inside the Microchip PIC interrupt function, the pointer reads the UART register and deference it to BUFFER[] array according to my code:

*PTR=rcreg; PTR++;

I then check the data in function main():

for(i=0;i<3;i++){ if(BUFFER[i]==DATA[i]){ k++; if(k==2){LED_On();} } }

and set ptr to point at the start address of BUFFER[]

ptr=BUFFER;

Question: Is this the best way and correct way to read data in the register? How can I use pointer in interrupt function?

Thank you for your kind attention and help in advance!

Please make some effort to format code properly. Dumping a single-line for...if...if... on people is no way to ask for help. — Marcelo Cantos
– Marcelo Cantos, Commented Oct 7, 2011 at 13:01

Community · Accepted Answer · 2017-05-23 12:19:56Z

0

You may want to consider implementing a lock-free circular buffer to transfer data between the ISR and main():
Circular lock-free buffer
Non-blocking algorithm

edited May 23, 2017 at 12:19

CommunityBot

11 silver badge

answered Oct 7, 2011 at 13:10

Alexey Frunze

62.4k14 gold badges90 silver badges190 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Lundin Over a year ago

But it probably has to have a "lock" (semaphore/mutex) since it is shared by an ISR and main(). You will get problems if the ISR is writing to the buffer while main is reading it at the same time.

Alexey Frunze Over a year ago

@Lundin: If done properly and there are no odd cache effects to workaround, no locks are needed (atomic r/w/increment are sufficient) as long as there's only one reader and one writer for each such buffer. I've done it on a few platforms (x86 and TMS32054xx).

Lundin Over a year ago

The problem isn't really whether the access instructions are atomic or not, but rather that the UART may get an interrupt at any given time and overwrite the data stored. You will have some sort of lock and perhaps also double buffers to avoid that. And have in mind that this is a PIC, which is about as far from x86 as you get. The PIC is so painfully slow at executing code, that it may even be too slow to catch up with common RS-232 baudrates.

Alexey Frunze Over a year ago

@Lundin: if your code can't keep up with your data rates and the buffer overflows (7 bytes are probably too few to accommodate latencies), something's seriously wrong. Btw, control flow can help here (when you're close to filling the buffer completely, drop DTR/DSR/whatever to signal to the transmitter that the receiver isn't ready).

Lundin Over a year ago

115200bps is a common baudrate which means you'll be getting a new byte every 87us (1/115200 * 10 bits). I think that's going to be tough to handle for most 8-bitters, PIC in particular. A large hardware input buffer in the UART peripheral on the MCU will help a lot - I don't know if PIC has this or not.

Collectives™ on Stack Overflow

Global Variable Pointer to array in Sourceboost C

1 Answer 1

5 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Linked

Related