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    PSoC4: GSM Modem


      Hi All !


      I am quite near to complete the GSM Project. I am not getting desired results as of now. The project which I designed, sends message to Cellular Phone when a push button is pressed. It receives message from Celllular Phone also. It displays it on LCD. Currently I am facing a problem in which I am able to send the message as many times as I press the pushbutton, but not able to receive it and display it on LCD once I send a message priorly. Please find attached my project. I request all to contribute, so we can make a GSM Module for PSoC4.







        • 1. Re: PSoC4: GSM Modem

          There is one thing I would do differently: You reset the interrupt and then you remove the cause by reading off the character in your handler
           I would first remove the cause and then the symptom.(Rocky Hooror Picture Show Theorem)





          • 2. Re: PSoC4: GSM Modem

            Well,not  just for the cosmetics: in the default branch of your switch(fsm) set the variable fsm to a legal value or you would loop forever.
            A de-bouncing of your pushbutton would be a suggestion. You will always get more than one pulse within a few ms. Easiest is a delay (in main, not in the handler!!!).





            • 3. Re: PSoC4: GSM Modem

              You need to set the UART ISR to level triggered, from datasheet of


              UART SCB -





              • 4. Re: PSoC4: GSM Modem

                Thank you for the suggestions. I just came to know that if the received data is greater than 4 bytes, an internal UART interrupt gets activated. In my project, when I receive the message on GSM Modem from a phone and read it using UART interrupt, the number of characters read are beyond the count 32, means it goes beyond 4 bytes. Perhaps that is why I am able to read the message on LCD only once even if I am clearing the UART Rx Buffer in the interrupt with the API UART_GSM_SpiUartClearRxBuffer();. After that I can see that the control of code goes in the UART interrupt, but it does not SET the read_message_status FLAG as the LCD does not show the message. Please find attached the project modified as per the suggestions of Bob and Dana (the solutions improved the code and I thank them for that).







                • 5. Re: PSoC4: GSM Modem

                  Its probably reading more chars because the buffer is not null terminated ? This


                  problem occurs when trying to print using a stirng API and the string is not NULL






                  So whenever you clear/init the string buffer fill it with '\0' (NULL) chars, then as


                  you read from UART you will simply overwrite the NULLS and as long as you


                  do not read a total of chars > ( bufferlen - 1 ) it will always be a NULL terminated


                  string. Each time you use string and want to get ready for next string reload


                  the buffer with NULLS.




                  Regards, Dana.

                  • 6. Re: PSoC4: GSM Modem

                    @Dana: I tried with your suggestion of clearing the buffer array after reading it, but I am still getting the same output.


                    As per GSM message rule, every message that GSM module sends to UART, starts with <CR><LF> and ends with <CR><LF> where CR is "Carriage Return" and LF is "New Line Feed". So I have set code according to this standard in my UART Receiver ISR where I am extracting the message from the received data. I am programming the project with below mentioned steps:


                    1. Setting GSM Module in Text mode (SIM300sendcommand(CMGF1)).


                    2. Deleting the message at Slot number 1 of GSM (SIM300DeleteMsg()).


                    3. Clearing the receiver and transmitter buffers (UART_GSM_SpiUartClearRxBuffer(), UART_GSM_SpiUartClearTxBuffer())


                    4. If(pushbutton is pressed) -> Set the mobile number (SIM300sendcommand(CMGS1)) -> send the message   (SIM300sendcommand(MESSAGE1)).


                    5. If(message from phone is received on GSM Module) -> Send command from PSoC4 to GSM Module to read it (the message is stored on Slot 1) (SIM300ReadMsg()) -> Put the received message on LCD (DisplayOnLCD(1u, 0u, (char *)message)) -> Delete the message at slot 1 (SIM300DeleteMsg())


                    Currently I am facing a problem in which I have 2 things to get solved:


                    (A) If after power up, I press the pushbutton and send message from GSM Modem to phone, I get the message on phone. But after that if I send message from phone to GSM Modem, I am not able to read it on LCD despite getting the successful message delivery on phone as well as being able to see through LED blink that it has been received on UART. I can send message successfully from GSM Modem to phone as many times as I wish.


                    (B) If after power up, I send message from phone to GSM Modem, I am able to see it on LCD. I am also able to send the message from GSM Modem to phone through push button press afterwards. But here, I can not get the same message on GSM Modem through phone afterwards. The point is I am not able to get message on GSM Modem multiple times though I can send message successfully from GSM Modem to phone as many times as I wish.




                    Please find attached the above stated functioning fulfilling project.







                    • 7. Re: PSoC4: GSM Modem

                      Hi Shaunak,


                      I think, best will be to do a hand-simulation of your rx-handler to see that it will not behave as you want.


                      Write down two or three messages with 0x0d and 0x0a in the corresponding positions and your (shortened) text in between. Write down the changed value of fsm and use it at the next cycle.


                      You cannot do that with breakpoints in debug mode, because the modem keeps on sending bytes while the PSoC is halted.


                      A way out could be


                      Not using the interrupt, increasing the rx-buffer of the component to two times the message length.


                      Poll in main() the Rx_BufferSize() which will not return the buffer's size but the number of characters in the buffer. When there is a complete message in the buffer start to read off the characters using ch = (uint8)(UART_GSM_GetByte() & 0x00ff) and handle that as you did in your interrupt handler before.





                      • 8. Re: PSoC4: GSM Modem

                        This is just a minor observation, this code line (30) is doubly terminated -




                        volatile char message[512];;


                        should be -




                        volatile char message[512];




                        Also noticed on system tab of .cydwr file your heap size is 128 bytes, you might want


                        to increase that.




                        Regards, Dana.

                        • 9. Re: PSoC4: GSM Modem

                          Here you do not terminate these with NULL, so when you use strglen() to


                          determine length of message to send you will get indeterminate results.


                          You will have to increase array sizes by +1 to accomidate the NULL character.








                          char CMGF1[10] = {'A','T','+','C','M','G','F','=','1',0x0D}; /*  Command: AT+CMGF=1 'Carriage Return'  */
                          char CMGS1[21] = {'A','T','+','C','M','G','S','=','"','0','0','0','0','0','0','0','0','0','0','"',0x0D}; /*  Command: AT+CMGS="0000000000" 'Carriage Return'. Here 0000000000 refers to the 10-digit phone number  */
                          char MESSAGE1[25] = {'B','I','G',' ','H','E','L','L','O',' ','F','R','O','M',' ','P','S','o','C',' ','4',' ','!','!',0x1A};  /*  "MESSAGE SENT FROM MODEM" '^Z'. This is the message sent  */
                          char CMGD1[10] = {'A','T','+','C','M','G','D','=','1',0x0D};/* Delete Message at Slot 1 of GSM Modem*/
                          char CMGR1[10] = {'A','T','+','C','M','G','R','=','1',0x0D};/* Read Message at Slot 1 of GSM Modem*/




                          Regards, Dana.

                          • 10. Re: PSoC4: GSM Modem

                            I think it's more convenient: (0x0d = \015 oct       or  \x0d     in hex)


                            char AT1[3] = "AT\015 ;


                            char CMGF1[10] = "AT+KMGF=1\x0d";


                            char CMGS1[21] = "AT+KMGS=0000000000\015";


                            char MESSAGE1[25] = "BIG HELLO FROM PSoC 4!!\032";


                            char CMGD1[10] = "AT+KMGD=1\015";


                            char CMGR1[10] = "AT+KMGR=1\015";

                            • 11. Re: PSoC4: GSM Modem

                              @Pav, I did not realize you could use the backslash in a string


                              like that. I kept looking at his strings thinking the same, way too


                              much typing.




                              Thanks for the post.




                              Regards, Dana.

                              • 12. Re: PSoC4: GSM Modem

                                I needed to connect the battery to the contact VBTA.
                                Otherwise - after the first activation of the transmitter modem stops responding.

                                • 13. Re: PSoC4: GSM Modem

                                  Your module says that it is a SIM900 but your code states that it is a SIM300 in the top part of the main.c but later it has code for a SIM900.  Are the commands the same between them? Also where did you get the module?  I would like to check out the program and see how it works.

                                  • 14. Re: PSoC4: GSM Modem

                                    Here is a data sheet for the SIM900.

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