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chingB
Joined: 29 Dec 2003
Posts: 81
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| #int_rda help |
 Posted: Fri Jan 16, 2004 4:28 am |
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hello...
I have a code that will receive packets from a PC. The packet send by the PC is of variable length but not exceeding 64bytes.
Code list:
| Code: |
#define RX_SIZE 64 // RS485 buffer for serial reception
byte rxbuffer[RX_SIZE]; // RS485 serial RX buffer
byte rx_in = 0; // RS485 RX data IN index
byte rx_out = 0; // RS485 RX data OUT index
#int_rda
void rx_isr() // RS485 serial RX interrupt service routine
{
int t; // local data storage
if (kbhit(Com1))
{
t = fgetc(Com1); // get rx data and save to buffer
rxbuffer[rx_in] = t ; // and save to buffer
t = rx_in; // save current rx index
rx_in = (rx_in+1) % RX_SIZE; // increment index
}
}
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My concern is? how can I able to detect that their is no character send by the PC? and How can I incorporate a flag that will prevent a multi-trigger of another packet while the program process the previous packet?
BTW, I am using PIC18F452 at 20MHz clock.
Need your info, comments and/or suggestions.
Thank you. |
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Ttelmah
Guest
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| Re: #int_rda help |
| Posted: Fri Jan 16, 2004 4:37 am |
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| chingB wrote: | hello...
I have a code that will receive packets from a PC. The packet send by the PC is of variable length but not exceeding 64bytes.
Code list:
| Code: |
#define RX_SIZE 64 // RS485 buffer for serial reception
byte rxbuffer[RX_SIZE]; // RS485 serial RX buffer
byte rx_in = 0; // RS485 RX data IN index
byte rx_out = 0; // RS485 RX data OUT index
#int_rda
void rx_isr() // RS485 serial RX interrupt service routine
{
int t; // local data storage
if (kbhit(Com1))
{
t = fgetc(Com1); // get rx data and save to buffer
rxbuffer[rx_in] = t ; // and save to buffer
t = rx_in; // save current rx index
rx_in = (rx_in+1) % RX_SIZE; // increment index
}
}
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My concern is? how can I able to detect that their is no character send by the PC? and How can I incorporate a flag that will prevent a multi-trigger of another packet while the program process the previous packet?
BTW, I am using PIC18F452 at 20MHz clock.
Need your info, comments and/or suggestions.
Thank you. |
1) Consider flow control.
2) Do a search back through the archives. Neutone (I think), published a very tidy combination of buffered receive, with a timer based 'time out'.
Best Wishes |
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chingB
Joined: 29 Dec 2003
Posts: 81
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| Posted: Fri Jan 16, 2004 5:46 am |
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Hi,
I got the code of neutone... listed below:
| Code: |
#int_TIMER1 //*********************************
TIMER1_isr() // 1.5 byte periods after last byte I&O
{ disable_interrupts(int_TIMER1); // TMR1 Overflow Interrupt Enable bit off
PacketA_Byte_Count=PacketA_Index; // Store length of packet
if (PacketA_TX) // Has last bit cleared transmit shift buffer?
{ PacketA_TX=0; // Turn off 485 transmitter driver
}
else // Incomming packet recieved?
{ PacketA_IN=1; // Tag packet for processing
}
}
#int_RDA //**************
RDA_isr() // BYTE RECEIVED
{ PacketA_Data=fgetC(chanA); // Store incoming byte
if(!PacketA_IN&&!TXIE) // Don't receive transmitting noise or overrun last packet
{ if(bit_test(RS232_ERRORS,2)) // Check for framing errors
{ if (++PacketA_Errors & 8) // If 32 errors
{ if(!(PacketA_Baud & 16)) // is baudrate locked
{ if(++PacketA_Baud & 8)
PacketA_Baud=0;
if(PacketA_Baud==0)
{ Set_UART_Speed(57600,chanA);
PacketA_timeout=64128;
}
if(PacketA_Baud==1)
{ Set_UART_Speed(38400,chanA);
PacketA_timeout=63424;
}
if(PacketA_Baud==2)
{ Set_UART_Speed(28800,chanA);
PacketA_timeout=62720;
}
if(PacketA_Baud==3)
{ Set_UART_Speed(19200,chanA);
PacketA_timeout=61312;
}
if(PacketA_Baud==4)
{ Set_UART_Speed(9600,chanA);
PacketA_timeout=57088;
}
if(PacketA_Baud==5)
{ Set_UART_Speed(4800,chanA);
PacketA_timeout=48640;
}
if(PacketA_Baud==6)
{ Set_UART_Speed(2400,chanA);
PacketA_timeout=31744;
}
if(PacketA_Baud==7)
{ Set_UART_Speed(1200,chanA);
PacketA_timeout=0;
}
}
}
}
PacketA[PacketA_Index++]=PacketA_Data; // Place incoming byte in Packet Buffer
set_timer1(PacketA_timeout); // Wait 1.5 byte periods then interrupt
TMR1IF=0; // Clear timer1 overflow Interrupt Flag bit
enable_interrupts(int_TIMER1); // TMR1 Overflow Interrupt Enable bit on
}
}
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set_timer1(PacketA_timeout); ---> how can I compute for timer1 using PIC18F452 at 20MHz clock? what would be the difference if I use timer3 instead of timer1?
Is timer1 calculation has a correlation with the baudrate for serial communication? What would the calculation in order to have 1.5bytes period for either timer1 or timer3?
I notice that the code use PacketA_TX=0; as flow control for transmit and receive packet. I don't see any point on how I can detect that PC has already stop sending data? I can't figure out the code for multi-trigger prevention.
In addition, I plan to use a 115,200bps baudrate for the UART.
Any help please....
Thnx |
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Neutone
Joined: 08 Sep 2003
Posts: 839
Location: Houston
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| Posted: Fri Jan 16, 2004 8:58 am |
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| chingB wrote: | Hi,
I got the code of neutone... listed below:
| Code: |
#int_TIMER1 //*********************************
TIMER1_isr() // 1.5 byte periods after last byte I&O
{ disable_interrupts(int_TIMER1); // TMR1 Overflow Interrupt Enable bit off
PacketA_Byte_Count=PacketA_Index; // Store length of packet
if (PacketA_TX) // Has last bit cleared transmit shift buffer?
{ PacketA_TX=0; // Turn off 485 transmitter driver
}
else // Incomming packet recieved?
{ PacketA_IN=1; // Tag packet for processing
}
}
#int_RDA //**************
RDA_isr() // BYTE RECEIVED
{ PacketA_Data=fgetC(chanA); // Store incoming byte
if(!PacketA_IN&&!TXIE) // Don't receive transmitting noise or overrun last packet
{ if(bit_test(RS232_ERRORS,2)) // Check for framing errors
{ if (++PacketA_Errors & 8) // If 32 errors
{ if(!(PacketA_Baud & 16)) // is baudrate locked
{ if(++PacketA_Baud & 8)
PacketA_Baud=0;
if(PacketA_Baud==0)
{ Set_UART_Speed(57600,chanA);
PacketA_timeout=64128;
}
if(PacketA_Baud==1)
{ Set_UART_Speed(38400,chanA);
PacketA_timeout=63424;
}
if(PacketA_Baud==2)
{ Set_UART_Speed(28800,chanA);
PacketA_timeout=62720;
}
if(PacketA_Baud==3)
{ Set_UART_Speed(19200,chanA);
PacketA_timeout=61312;
}
if(PacketA_Baud==4)
{ Set_UART_Speed(9600,chanA);
PacketA_timeout=57088;
}
if(PacketA_Baud==5)
{ Set_UART_Speed(4800,chanA);
PacketA_timeout=48640;
}
if(PacketA_Baud==6)
{ Set_UART_Speed(2400,chanA);
PacketA_timeout=31744;
}
if(PacketA_Baud==7)
{ Set_UART_Speed(1200,chanA);
PacketA_timeout=0;
}
}
}
}
PacketA[PacketA_Index++]=PacketA_Data; // Place incoming byte in Packet Buffer
set_timer1(PacketA_timeout); // Wait 1.5 byte periods then interrupt
TMR1IF=0; // Clear timer1 overflow Interrupt Flag bit
enable_interrupts(int_TIMER1); // TMR1 Overflow Interrupt Enable bit on
}
}
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set_timer1(PacketA_timeout); ---> how can I compute for timer1 using PIC18F452 at 20MHz clock? what would be the difference if I use timer3 instead of timer1?
Is timer1 calculation has a correlation with the baudrate for serial communication? What would the calculation in order to have 1.5bytes period for either timer1 or timer3?
I notice that the code use PacketA_TX=0; as flow control for transmit and receive packet. I don't see any point on how I can detect that PC has already stop sending data? I can't figure out the code for multi-trigger prevention.
In addition, I plan to use a 115,200bps baudrate for the UART.
Any help please....
Thnx |
PacketA_TX is the pin that turns the 485 driver chip to transmit.
Timer 3 will work just as well as timer 1.
I was using a clock of 19660800hz so 20Mhz would use the same timer preloads just fine.
If you plan to run at 115,200bps baudrate you should not use this routine. I had a lot of timing issues with getting into and out of the interupt code at that baud rate. |
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chingB
Joined: 29 Dec 2003
Posts: 81
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| Posted: Fri Jan 16, 2004 5:41 pm |
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Hi,
Can you provide me a math calculation for the values of PacketA-timeout. Do you have any idea on how I can prevent muti-trigger of packet?
Thanx |
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Neutone
Joined: 08 Sep 2003
Posts: 839
Location: Houston
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| Posted: Mon Jan 19, 2004 8:55 am |
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The timer counts up from 0 to 65536 it then overflows to 0 and interupt occures.
With the timer set to increment every instruction cycle what value do you preload to cause the timer to interupt after a specified period?
The byte period is 1mS for 9600 baud.
The timeout period is 1.5 byte periods.
There are 1 instruction cycle in 0.25 uS at 20Mhz crystle.
There are 6000 instruction cycles in in 1.5mS.
The value to preload for for 9600 baud is 65536-6000.
This assumes a byte stream on the serial port. You can not get this to work if the bytes arrive with a pause between them.
To prevent multitrigger of packets do not clear the packet in flag untill the packet has been fully processed. |
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