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Using SMP: (SYS$SAMP.LDD), the sound sampling device driver =========================================================== Files in this zip (TSMP10.ZIP) ------------------------------ README.TXT This documentation SYS$SAMP.LDD The device driver itself SAMPLER.H Header file (for C programming) TSMP.IMG Example code ready build TSMP.C Source of example code (C) TSMP.OPL Example code (OPL) TSMP2.OPL A second Opl example program The basic idea of sound samples ------------------------------- When the microphone is enabled, a "sound value" is provided, by the hardware, once every 8000th of a second. This sound value is actually provided as an ALAW encoded byte (8 bit value). The PLIB function p_recordsoundw (and related functions) write series of these sound values (or "sound samples") direct to a nominated file. However, using SMP:, you can have these values placed into a buffer in your dataspace, that you can analyse directly. You can either analyse these ALAW encoded values directly, or you can have SMP: return a buffer of decoded values - where the decoded values are 13 bit numbers in the range -4096 to +4096. Once you have opened a channel to SMP:, you can use code as simple as p_read(pcb,&buf[0],len); to read 'len' consecutive samples into a buffer. The largest allowed value of 'len' is 4000, in which case the data in buf[] represents half a second of sound. The supplied test program TSMP ------------------------------ Copy TSMP.IMG into an \IMG\ directory. Copy SYS$SAMP.LDD into the root directory on the same device. Go to the RunImg icon, highlight "Tsmp", and press Enter. Press Enter again to accept the initial suggestion. You will see a continually refreshed graph of the sound going into the microphone at that very moment. Try whistling, talking, or making other noises. Exit the application from the Shell when you are bored with it. Note that after you exit TSMP, by default the SMP: device driver is left loaded in memory (using up around 6k of RAM). To clean this up, run the program again, but choose Esc at the initial query alert. If you make a very short sound, TSMP may fail to pick this up - this is because TSMP *doesn't* monitor SMP: continuously - it spends a lot of time drawing its graph instead. But you could rewrite TSMP in order to be more responsive. Ie it could avoid making any display until the sound reached a higher threshold. It could improve its performance even further by reading and analysing the ALAW encoded values directly, which is a faster service that reading the decoded values. Warning: TSMP will keep your S3a switched on! Be sure to exit it! Also, while it's running, it will prevent any other access to the sound system on the S3a - so no alarms will sound, etc. The C source code and the Opl source code ----------------------------------------- The code in TSMP.C and TSMP.OPL corresponds in all essential details. (Except that the C code runs in "compatibility mode".) For simplicity, I shall just describe the services of SMP: in terms of the C interface. (Though I have provided TWO Opl example programs, and only one in C.) Basic pattern of use of SMP: ---------------------------- Before you can use any of the services of SMP:, you have to open a channel to it, using p_open. Eg LOCAL_C VOID OpenChannel(VOID) { INT ret; ret=p_open(&pcb,"SMP:",-1); if (ret) Panic(ret,"Failed to open channel to SMP"); } This writes back into pcb the "handle" (the "Pointer to the Control Block") that you use in all subsequent p_read, p_iow, p_close (etc) calls to SMP:. Before you can open a channel to SMP:, however, you have to ensure that the device driver SYS$SAMP.LDD has been loaded into memory. Eg LOCAL_C VOID LoadDriver(VOID) { INT ret; TEXT buf[P_FNAMESIZE]; p_fparse("\\sys$samp.LDD",DatCommandPtr,&buf[0],NULL); ret=p_loadldd(&buf[0]); if (ret && ret!=E_FILE_EXIST) Panic(ret,"Failed to load SYS$SAMP.LDD"); } SMP: keeps recording samples internally all the time ---------------------------------------------------- SMP: can have up to four open channels, from four different applications at the same time. Whenever there is at least one open channel to SMP:, it keeps recording sample values internally. These values then get written into applications' buffers when requested. SMP: only keeps half a second's worth of samples, however. Three modes of using SMP: ------------------------- In the default mode ("P_SAMPLES_SINCE_LAST"), you ask for a fixed number of samples, and you at once get given either this number of samples, or as many as have been collected since the last time you requested samples (if this is less). In the mode P_SAMPLES_FROM_LAST, you definitely get given the number of samples you ask for, starting from the last time you requested samples, and the call only completes when the required number of samples is ready. In the mode P_SAMPLES_FROM_NOW, the same applies, but the samples only start from "now". How to change the mode ---------------------- You use the P_FSET function. Thus p_iow3(pcb,P_FSET,mode); You can also sense the mode, using WORD mode; p_iow3(pcb,P_FSENSE,&mode); Reading and "super-reading" --------------------------- The call p_read(pcb,&buf[0],len); is just equivalent, as always, to p_iow4(pcb,P_FREAD,&buf[0],&len); Here, len is the number of WORDs of data in buf[]. If you prefer, you can use P_FRSUPER instead of P_FREAD, to read a number of BYTEs of ALAW encoded data - as discussed earlier. In this case, there is no utility function p_read - you have to use the p_iow (or p_ioc etc) call. In either P_FREAD or P_FRSUPER, the number of samples actually delivered is written back to the 'len' variable. Note that only a single P_FREAD or P_FRSUPER per open channel should be pending at any one time. Technical note -------------- The "ALAW encoded data" provided by P_FRSUPER isn't exactly the same as provided by the raw CODEC hardware. The value is inverted and then "magic xor-red" (to XOR all the even bits), before being returned to the application. This means that a louder sound will give rise to a larger value. (In contrast, the bytes written to file by services such as p_recordsoundw are *exactly* as provided by the CODEC.) Synchronous and asynchronous calls ---------------------------------- Like all device drivers, SMP: supports asynchronous versions of its services as well as synchronous ones. And you can P_FCANCEL an outstanding asynchronous request. Special utility conversion services ----------------------------------- SMP: also provides a couple of conversion services, to convert a buffer of WORDs of decoded data into another buffer of BYTEs of ALAW encoded data, and vice versa. These services both use the P_CONVERT struct, defined in the header file SAMPLER.H: typedef struct /* Conversion structure */ { VOID *Source; VOID *Destination; } P_CONVERT; For example, BYTE aLaw[4]; WORD Data[4]; P_CONVERT Conversion; Len=4; Conversion.Source=&Data[0]; Conversion.Destination=&aLaw[0]; p_iow4(pcb,P_FCONVERT_TO,&Conversion,&Len); Conversion.Source=&aLaw[0]; Conversion.Destination=&Data[0]; p_iow4(pcb,P_FCONVERT_FROM,&Conversion,&Len); Values of some #define's (for Opl programmers) ---------------------------------------------- #define P_FREAD 1 #define P_FCANCEL 4 #define P_FSET 7 #define P_FSENSE 8 #define P_FRSUPER 13 An example program using "super-reading" ---------------------------------------- Have a look at TSMP2.OPL. Try to figure out what happens when you run it, and then run it and see if you were right. Some of the limitations in the performance in TSMP2.OPL are due to time wasted scanning the buffer for large values. This time could be cut down by programming in C, or by creating some machine code and accessing that using USR. Disclaimer ---------- Psion will not be held responsible for any loss of data as a result of use of SYS$SAMP.LDD, which is still to an extent in an experimental phase. SYS$SAMP.LDD is not an official Psion product. It has not yet been exhaustively tested, and cannot be relied upon eg not to reset your S3a occasionally. Distribution ------------ You can freely distribute the file TSMP10.ZIP, but all the files in it should be kept together. These notes prepared -------------------- By David Wood, Psion Product Development, 24th March 1994. Revised, 6th April 1994 (TSMP2.OPL added.) All comments, bug reports etc welcome by EMAIL (eg CiX) ONLY.