{"id":2310,"date":"2025-04-15T09:54:40","date_gmt":"2025-04-15T09:54:40","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&p=2310"},"modified":"2025-06-11T06:03:58","modified_gmt":"2025-06-11T06:03:58","slug":"acomrx_strfind-ppc-d28","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/programming-reference\/instructions-arranged-by-function\/communications-instructions\/any-serial-port\/acomrx_strfind-ppc-d28\/","title":{"rendered":"aComRx_StrFind pp,c [D>=28]"},"content":{"rendered":"\n

Match a received string to a table in NVEM<\/a>. This is subtly different to <\/em>aComRx_StrFind2<\/a><\/code>, which uses a different table format<\/em>. The ‘a’ first letter of the keyword indicates that this is the “addressable” version, meaning the instruction can address a serial port other than the default.<\/p>\n\n\n\n

This instruction seeks to match the data at the head of the serial Rx buffer for port pp <\/strong>with one or more “canned” strings stored in NVEM. Its primary use is for detecting received commands and machine generated ASCII messages. For example, we initially created it to assist in interacting with a cellular modem, for sending and receiving SMS messages.<\/p>\n\n\n\n

If argument c is zero, the instruction treats upper and lower case letters as equivalent. If c is non-zero, the case of the received string must match exactly the string stored in NVEM.<\/p>\n\n\n\n

The data in NVEM must be stored in a very specific “NULL terminated” format. This is best illustrated by an example. Lets say we want to detect which fruit has been requested, typed in on a terminal emulator and ending in a carriage return (‘0D or 13)<\/p>\n\n\n\n

1. NVEM: Message list<\/h6>\n\n\n\n

First you construct a list of all possible receive strings in NVEM<\/a>. Each string must be terminated with a 0 byte. The 0 is not part of the string, it merely signals the end of the string (C-style NULL terminated strings).<\/p>\n\n\n\n

strOrange:      NV0Byte   \"Orange\",13,0\nstrApple:       NV0Byte   \"Apple\",13,0\nstrBanana:      NV0Byte   \"Banana\",13,0\nstrLemon:       NV0Byte   \"Lemon\",13,0\nstrPear:        NV0Byte   \"Pear\",13,0\nstrGrape:       NV0Byte   \"Grape\",13,0\n;        Terminator _________________^<\/pre>\n\n\n\n
2. NVEM: Pointer table<\/h6>\n\n\n\n
Next you construct a table, in NVEM, of pointers to the individual strings. This must be terminated in two 255 bytes. The 255s tell aComRx_StrFind<\/code> that it has come to the end of the table.<\/p>\n\n\n\n
FruitNames:     NV0Ptr    strOrange\t;Entry #1\n                NV0Ptr    strLemon \t;Entry #2\n                NV0Ptr    strApple \t;Entry #3\n                NV0Ptr    strPear  \t;Entry #4\n                NV0Ptr    strBanana\t;Entry #5\n                NV0Ptr    strGrape \t;Entry #6\n                NV0Byte   255,255      ;<<<<< Essential!!!<\/pre>\n\n\n\n
You will notice that the order of entries is different to the order of the strings themselves. They can be in any order you like, and you can have several such tables, with different ordering, even different sets of strings.<\/p>\n\n\n\n
3. Code: Wait for a message string<\/h6>\n\n\n\n
Now to your actual code (the above is tables, not executable code). The first thing your code needs to do is wait until it knows there’s a string the the Rx buffer, ready to be interpreted. In this case we know that a carriage return signals the end of an incoming string in the Rx buffer. Hence, we might wait until there is a carriage return present. Let’s say this is a MultiTrack task, so we simply write a loop that waits for the carriage return, thus:<\/p>\n\n\n\n
COM1            EQU               252        ;Address of the required serial port                
CRWait:         YieldTask<\/a>
                LoadX             13         ;Carriage return 
                aComRx_FindXInBuf COM1       ;Is there a CR in the Rx buffer?
                GoIfXEQ<\/a>           255,CRWait ;loop back if not<\/pre>\n\n\n\n
This code snippet will sit and loop until a CR appears. Then it will “fall through”. Once it falls through we now for sure that there is a message waiting for us (barring something going wrong!).<\/p>\n\n\n\n
4. Code: Find a string match.<\/h6>\n\n\n\n
This is where we use the actual ComRx_StrFind<\/code> instruction. First we have to make sure the NVEM access is correctly set up.<\/p>\n\n\n\n
                NVSetPtr<\/a>          FruitNames
                NVSetPage         0           ;0 is the default, so playing very safe!
                aComRx_StrFind    COM1,0      ;Seek a match between Rx buffer and the tabulated strings<\/pre>\n\n\n\n
5. Code: Evaluate the result.<\/h6>\n\n\n\n
The\u00a0ComRx_StrFind<\/code>\u00a0returns its result in\u00a0X<\/a>, as follows:<\/p>\n\n\n\n