How to read a 1-wire sensor with C on a Raspberry Pi
Bill Thanis
qwerty172-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org
Fri Jan 17 17:23:48 UTC 2014
You could open the file descriptor and use the select() call to wait on
input. When I wrote multithreaded servers, I would use this with the
non-blocking mode. In your case, you probably want to set a timeout on the
select(). If the timeout occurs, you do something, if the FD is ready to be
read you read it and do something else.
I'll try to dig up the code tonight, but in my case this was
- open the sockets (or any other file descriptor)
- add the FD to the select() as read
- call select() to wait.
- when select ends.
- check if it was a read opportunity.
- if yes spawn a thread (or pass the read FD to a thread) to be read and do
something with the data.
- check if it was a timeout (because a timeout and a read opportunity can
happen simultaneously, which I found out the hard way).
- if yes do what you do on a timeout
- go back to wait on select()
I'm not sure this will help, but its my $0.02.
Bill
On Fri, Jan 17, 2014 at 10:17 AM, Mel Wilson <mwilson-Ja3L+HSX0kI at public.gmane.org> wrote:
> On Thu, 2014-01-16 at 21:25 -0500, Jamon Camisso wrote:
> > On 16/01/14 08:43 PM, Mel Wilson wrote:
> > [ ... ]
> > I'm using a DS18B20 as well, hence that float rounding - it's supposed
> > to be accurate to +/- 0.5C through most of it's range, but I've measured
> > with other thermometers and it's close enough to 1/10th for my purposes.
> >
> > I've used it with an Ardunino as well with the Dallas 1-wire scanning
> > library. Is that what you used?
>
> My apologies. I'm way too shambolic in running these projects. The
> RHT03 temperature/humidity sensor (with its host of part-numbers) with
> the Arduino is the setup I've got results from. My DS18B20 project is
> still only prototype code that will be run on an AVR. Both of these
> setups use bit-banged interfaces.
>
> You're working farther up the food chain than I am.
>
> Without actual results, just to post something, here's my initial
> DS18B20 code (Some of those newlines are from the mail client. Can't
> get them out):
>
>
> //=====================================
> #ifndef DS18B20_H
> #define DS19B20
>
> #include <stdint.h>
>
> typedef uint8_t romcode_t [8];
>
> extern void delay_msec (int msec);
> extern void delay_usec (int usec);
>
>
> void bus_setup ();
> uint16_t read_temperature (romcode_t device_rom);
>
> #endif // DS18B20
>
>
> //=====================================
> #include <stdint.h>
> #include "ds18b20.h"
>
> #define bit_set(F,B) (F |= (1<<(B)))
> #define bit_clr(F,B) (F &= ~(1<<(B)))
> #define bit_tst(F,B) (F & (1<<(B)))
> #define bit_val(F,B) (bit_tst(F,B) != 0)
> #define pin_clr(P) (bit_clr (P))
> #define pin_set(P) (bit_set (P))
>
> #define BUS_OUTPUT_PIN PORTB,2
> #define BUS_INPUT_PIN PINB,2
> #define BUS_DDR_OUT (bit_set (DDRB,2))
> #define BUS_DDR_IN (bit_clr (DDRB,2))
>
>
> void bus_setup ()
> {
> BUS_DDR_IN;
> pin_clr (BUS_OUTPUT_PIN);
> } // bus_setup
>
>
> static void bus_low ()
> {
> BUS_DDR_OUT;
> } // bus_low
>
> static void bus_release ()
> {
> BUS_DDR_IN;
> } // bus_release
>
> static uint8_t bus_pin ()
> {
> return bit_val (BUS_INPUT_PIN);
> } // bus_pin
>
> static void master_write (uint8_t bit_val)
> {
> bus_low();
> if (bit_val) { // write "1" bit
> delay_usec (2);
> bus_release();
> delay_usec (58);
> }
> else { // write "0" bit
> delay_usec (60);
> bus_release();
> }
> } // master_write
>
> static int master_read ()
> {
> uint8_t val;
> bus_low();
> delay_usec (1);
> bus_release();
> delay_usec (14);
> val = bus_pin();
> if (!val) // slave is driving bus pin low
> delay_usec (45);
> return val;
> }// master_read
>
> static uint8_t transaction_initialization()
> {
> uint8_t delay_count;
> uint8_t slave_present;
> bus_low();
> delay_usec (480); // reset pulse
> bus_release();
> while (!bus_pin()) ;
> delay_usec (14);
> slave_present = 0;
> for (delay_count=0; delay_count < 240; ++delay_count) {
> if (!bus_pin())
> slave_present = 1;
> }
> delay_usec (480 - 14 - delay_count);
> return slave_present;
> } // transaction_initialization
>
> static void transmit_uint8 (uint8_t data)
> {
> uint8_t i;
> for (i=0; i < 8; ++i) {
> master_write (data & 1);
> data >>= 1;
> }
> } // transmit_uint8
>
> static uint8_t receive_uint8 ()
> {
> uint8_t i, val;
> for (i=0; i < 8; ++i)
> val = val | (bus_pin() << i);
> } // receive_uint8
>
> uint8_t transaction (uint8_t rom_command, uint8_t function_command)
> {
> if (!transaction_initialization())
> return 0;
> transmit_uint8 (rom_command);
> return 1;
> } // transaction
>
> uint16_t read_temperature (const romcode_t *device_rom)
> {
> uint8_t scratchpad [9];
> if (!transaction_initialization())
> return 0xFFFF;
> transmit_uint8 (0x55); // Match ROM
> for (i=0; i < 8; ++i)
> transmit_uint8 (device_rom [8-i]);
> transmit_uint8 (0x44); // Convert T
> delay_msec (750); // delay until conversion has been finished
> transaction_initialization();
>
> transmit_uint8 (0x55); // match ROM
> for (i=0; i < 8; ++i)
> transmit_uint8 (device_rom [8-i]);
>
> transmit_uint8 (0xBE); // read scratchpad
> for (i=0; i < 9; ++i)
> scratchpad [9-i] = receive_uint8();
> // ??? verify checksum
> return scratchpad[1] << 8 | scratchpad[0];
> } // read_temperature
>
>
> --
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