CD245x DSP Tutorial
This page will give you an example of program (firmware) development using a CD2450A evaluation kit. The free version of the evaluation kit runs on any DOS based PC (Windows9X,ME,2000,NT,XP) and includes
- CD2450A Assembler/Linker (Free Version)
- CD2450A BUGSFINDER Program (Free Version)
One simple sin(wt) wave generator program will be developed using this evaluation kit through this page. The flow diagram of the development is shown in fig. 1. First, a program source file will be made using your favorite ASCII file editor. Then, the file is assembled/linked to get an object file. This object file can be downloaded to either a CD2450A emulator board (sold separately) directly for a real time operation, or BUGSFINDER simulator/debugger on PC. You can check the functions of the program through the PC screen in either case.
Fig.1
Demo Flow
Program Example (Sine wave generation)
This example gives a SIN(x) output to EXT0 register and RAM0:0001 address. A -1 to +1 angle input is projected to -pi to +pi. In other word, the input values are scaled by 1/pi. There is a simple and common algorithm to generate a Sin value as in Fig.2. 
Fig.2 Sin approximation algorithm.
- Coding Example.
# # Sin Pi*x generation example routine # (c)1994 Clarkspur Design, Inc. # # # # RAM0:0000 angle -1 to 1 # R2 incremental value # EXT0, RAM0:0001 output value # (Sin Routine) # AH Before:Angle Input After:Result sin(pi*x) # ldi st,'h0 ldsi r3,'h3ff #Stack Pointer ldsi r2,'h3f8 loop: ldsi r0,'h0 ld ah,(r0) add a,r2,rs8 ld (r0),ah modr r4,r2+! call @sin call @out bra @loop sin: ld r6,ah mod rs8 mod rs2 ansi a,'h3e # ~x * 2 -> AH addi a,@ttop # + Table_Top ld r1,ah # Pointer R1 for ~x ld ah,r6 andi ah,'h07ff # delta x mod ls2 # * 4 ld x,ah ldi y,'h6487 # * pi/4 ld ah,ph ld x,ph ld y,(r1+!)p # * Cos pi*~x ld ah,ph ld ah,ph add a,(r1+!)p # + Sin pi*~x ret out: ldsi r0,'h1 ld (r0),ah tgl ah,15 # Invert Sign bit ld ext0,ah # Output to ext0 ret ds 'h10 trap: bra @trap ttop: DW 'H7D00 DW 'H0000 # 0 DW 'H7A99 DW 'H1863 # 6.25E-002 DW 'H737C DW 'H2FD6 # .125 DW 'H67EF DW 'H4572 # .1875 DW 'H5863 DW 'H5863 # .25 DW 'H4572 DW 'H67EF # .3125 DW 'H2FD6 DW 'H737C # .375 DW 'H1863 DW 'H7A99 # .4375 DW 'H0000 DW 'H7D00 # .5 DW 'HE79D DW 'H7A99 # .5625 DW 'HD02A DW 'H737C # .625 DW 'HBA8E DW 'H67EF # .6875 DW 'HA79D DW 'H5863 # .75 DW 'H9811 DW 'H4572 # .8125 DW 'H8C84 DW 'H2FD6 # .875 DW 'H8567 DW 'H1863 # .9375 DW 'H8300 DW 'H0000 # -1 DW 'H8567 DW 'HE79D # -.9375 DW 'H8C84 DW 'HD02A # -.875 DW 'H9811 DW 'HBA8E # -.8125 DW 'HA79D DW 'HA79D # -.75 DW 'HBA8E DW 'H9811 # -.6875 DW 'HD02A DW 'H8C84 # -.625 DW 'HE79D DW 'H8567 # -.5625 DW 'H0000 DW 'H8300 # -.5 DW 'H1863 DW 'H8567 # -.4375 DW 'H2FD6 DW 'H8C84 # -.375 DW 'H4572 DW 'H9811 # -.3125 DW 'H5863 DW 'HA79D # -.25 DW 'H67EF DW 'HBA8E # -.1875 DW 'H737C DW 'HD02A # -.125 DW 'H7A99 DW 'HE79D # -6.25E-002
Now, try it on the simulator.
First, you need to assemble the source file. You can use "ASM2450.EXE" assembler program by typing> ASM2450 sin.s
where "sin.s" is the source file you have just made. The ASM2450 automatically generates two files , regardless of whether the assembly was or was not successful. One is an object file, the other a listing file. You can check the listing file to see Errors, if any. (But, please remember it does not necessarily mean your program has no error even if the ASM2450 does not point any error. Free version of the tools do not check the detailes of syntax error.) The default file names for those are sin.o and sin.l, though you can specify any legal name on them if you wish. (Please download Assembler Description from the "Literature" page.)
As more than one object file are linked together to form a final executable program in normal case, successive linkage processing is necessary for this purpose. Even if you have only one object file, you still need to go through the linkage process to generate an executable file. In this example, we try to link sin.o with an interrupt vector description object file. When you start the simulator later on, you can start your program by giving a reset signal on the net with this interrupt vector assignment. The CD2450 linker always requires a linkage spec file describing an output file name, series of input object file names, absolute program starting address etc..
- sin.l file
#01-31-1996 10:37:51 # # Sin Pi*x generation example routine # (c)1994 Clarkspur Design, Inc. # # # # RAM0:0000 angle -1 to 1 # R2 incremental value # EXT0, RAM0:0001 output value # (Sin Routine) # AH Before:Angle Input After:Result sin(pi*x) # 0000 0840 0000 ldi st,'h0 0002 7FFF ldsi r3,'h3ff #Stack Pointer 0003 5FF8 ldsi r2,'h3f8 loop: 0004 1C00 ldsi r0,'h0 0005 0210 ld ah,(r0) 0006 9252 add a,r2,rs8 0007 4210 ld (r0),ah 0008 1606 modr r4,r2+! 0009 48F0 000F call @sin 000B 48F0 0024 call @out 000D 4C00 0004 bra @loop sin: 000F 5312 ld r6,ah 0010 90D0 mod rs8 0011 9090 mod rs2 0012 B83E ansi a,'h3e # ~x * 2 -> AH 0013 8870 003B addi a,@ttop # + Table_Top 0015 5211 ld r1,ah # Pointer R1 for ~x 0016 1312 ld ah,r6 0017 A800 07FF andi ah,'h07ff # delta x 0019 9010 mod ls2 # * 4 001A 0021 ld x,ah 001B 0830 6487 ldi y,'h6487 # * pi/4 001D 0017 ld ah,ph 001E 0027 ld x,ph 001F 0A35 ld y,(r1+!)p # * Cos pi*~x 0020 0017 ld ah,ph 0021 0017 ld ah,ph 0022 8A75 add a,(r1+!)p # + Sin pi*~x 0023 0257 ret out: 0024 1C01 ldsi r0,'h1 0025 4210 ld (r0),ah 0026 EE1F tgl ah,15 # Invert Sign bit 0027 0081 ld ext0,ah # Output to ext0 0028 0257 ret 0029 0010 ds 'h10 trap: 0039 4C00 0039 bra @trap ttop: 003B 7D00 DW 'H7D00 003C 0000 DW 'H0000 # 0 003D 7A99 DW 'H7A99 003E 1863 DW 'H1863 # 6.25E-002 003F 737C DW 'H737C 0040 2FD6 DW 'H2FD6 # .125 0041 67EF DW 'H67EF 0042 4572 DW 'H4572 # .1875 0043 5863 DW 'H5863 0044 5863 DW 'H5863 # .25 0045 4572 DW 'H4572 0046 67EF DW 'H67EF # .3125 0047 2FD6 DW 'H2FD6 0048 737C DW 'H737C # .375 0049 1863 DW 'H1863 004A 7A99 DW 'H7A99 # .4375 004B 0000 DW 'H0000 004C 7D00 DW 'H7D00 # .5 004D E79D DW 'HE79D 004E 7A99 DW 'H7A99 # .5625 004F D02A DW 'HD02A 0050 737C DW 'H737C # .625 0051 BA8E DW 'HBA8E 0052 67EF DW 'H67EF # .6875 0053 A79D DW 'HA79D 0054 5863 DW 'H5863 # .75 0055 9811 DW 'H9811 0056 4572 DW 'H4572 # .8125 0057 8C84 DW 'H8C84 0058 2FD6 DW 'H2FD6 # .875 0059 8567 DW 'H8567 005A 1863 DW 'H1863 # .9375 005B 8300 DW 'H8300 005C 0000 DW 'H0000 # -1 005D 8567 DW 'H8567 005E E79D DW 'HE79D # -.9375 005F 8C84 DW 'H8C84 0060 D02A DW 'HD02A # -.875 0061 9811 DW 'H9811 0062 BA8E DW 'HBA8E # -.8125 0063 A79D DW 'HA79D 0064 A79D DW 'HA79D # -.75 0065 BA8E DW 'HBA8E 0066 9811 DW 'H9811 # -.6875 0067 D02A DW 'HD02A 0068 8C84 DW 'H8C84 # -.625 0069 E79D DW 'HE79D 006A 8567 DW 'H8567 # -.5625 006B 0000 DW 'H0000 006C 8300 DW 'H8300 # -.5 006D 1863 DW 'H1863 006E 8567 DW 'H8567 # -.4375 006F 2FD6 DW 'H2FD6 0070 8C84 DW 'H8C84 # -.375 0071 4572 DW 'H4572 0072 9811 DW 'H9811 # -.3125 0073 5863 DW 'H5863 0074 A79D DW 'HA79D # -.25 0075 67EF DW 'H67EF 0076 BA8E DW 'HBA8E # -.1875 0077 737C DW 'H737C 0078 D02A DW 'HD02A # -.125 0079 7A99 DW 'H7A99 007A E79D DW 'HE79D # -6.25E-002 Fatal Errors: 0 Warnings : 0 Notes : 0 ---- ASM2450 completed ---- - intv.l file
#01-30-1996 11:14:39 # # Interrupt Vector Default value. # 0000 8000 dw 'h8000 # Reset 0001 8000 dw 'h8000 # Int0 0002 8000 dw 'h8000 # Int1 0003 8000 dw 'h8000 # Int2 Fatal Errors: 0 Warnings : 0 Notes : 0 ---- ASM2450 completed ---- - sin.k file (Linkage spec. file.)
# # Sin Generation Program Linkage Spec. File # (c)1994 Clarkspur Design, Inc. # ->sin.x list->sin.ll org 8000 sin.o org fffc intv.o
> LINK2450 sin.k
to get an executable object file named sin.x. Please note the linker will quit the execution when it encounters any problem. Most common such problems come from the address overflow due to labels used in the short Immediate instructions, or missing designated files.The linked absolute object code can be downloaded to the CD2450A emulator for a real time execution. Use DNLD sin.x from the command prompt of the emulator control program (EC2450.EXE), or use Load sin.x at the command window of the BUGSFINDER to load the program on the simulator.
Simulation
Now, once you download the program on either H/W emulator or S/W simulator, you can run them to see the output waveform. For the simulator, you can set a break point where the output datum is ready at some register or RAM address, and write the datum into a file you specify. When break happens, you can check the condition then proceed to several action menus including collect data, plot on screen etc. Also, you can simulate interrupt generation by setting the break at every N cycles etc.. The Evaluation version of the BUGSFINDER is limited in its program size to 128 words, and the data memory size to 64 words each. All other functions are basically same as the full version except that the revision generation may be one year+ older than the latest version. You can set up the BUGSFINDER so that your output data from the program are accumulated in a file for the later analysis, or If you want see the output on-the-fly, you can set the BUGSFINDER to show it graphically, etc.. A very powerful break point function of the BUGSFINDER allows I/O simulation, waveform probing. up to your best imagination.
More Training
- Actually, the example program generates a "sweep" sin wave. (The angle speed parameter stored in R2 is incremented every time a new output data is computed.) Try to generate a single frequency sin wave by eliminating MOD R2 instruction in address 8. You can also change the frequency.
- If you have one hour free time, try to improve this program. You can minimize the distortion error by using bigger course sin table. You can eliminate cos table by knowing sin(x+pi/2) = cos(x). You can place the table on the data RAM to minimize the table look up time.
- Please refer to the test.l file from the assembler diskette, when you check the mnemonic of the assembler. As the free version of the assembler was made far before the development of the chip, some of the description differ from the CD2450A reference manual.
