Retrieved from ” https: This page was last edited on 23 January , at We do this by modifying our communications routine to send no blocks, but rather immediately start execution at the given address:. Here, however, is a summary of the algorithm the SPC uses:. It also manipulates the Audio ports, but this doesn’t seem to interfere with the memory transfer process, probably because the SNES is only listening for a certain value on Audio0. Here is the communication routine’s main loop, which sends a byte and waits for the SPC’s response, then updates the memory and counter values.
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Thus, when we execute the ROM, it tells us visually either that the music was loaded successfully or playyer execution halted somewhere in the music code. Then, we will make a slight modification to it that simplifies our code.
Here is the initialization phase, which waits until the SPC is ready to accept data, then sends the destination address. Note that we can swap the high and low bytes of a with the xba operation, even though a is in 8-bit mode at the time.
You could write a script to extract this data from the SPC file and turn it into a text file of assembly data directives, pplayer. Here is how we include the above data:. It also manipulates the Audio ports, but this doesn’t seem to interfere with the memory transfer process, probably because the SNES is only listening for a certain value on Audio0.
It performs the necessary initialization of the SPC:. This routine sends all the blocks at once.
With these initial definitions out of the way, we can write our routine. Now we write code to push the program spcc700 ward PSW register value onto the stack, so that we can pop it later. Thus, we define a location in the zero page where we can store the three bytes of a pointer to our source data:.
We will need to pass the source location, the destination location, and the length of the block to copy. Whether we restore the memory or DSP registers first doesn’t matter too much, but it will turn out to be convenient to restore the memory first.
We can’t pop the value until snex the other registers are restored, since the mov instruction that we use to restore them changes the PSW register. Alternatively, you could restrict yourself to copying blocks of less than bytes so that the counter never rolls over, or you could install a better communications routine in SPC RAM and use that instead.
While we are at it, we can define the values of the audio ports znes CPU flags, so that our code uses recognizable identifiers instead of hex values:. The advantage of including this graphics code is that it does something on the screen after the music loads.
Also, restoring the program counter means that the SPC then will be executing the stored code, not the communications routine, so we can’t send anything else after we have restored the program counter. When this happens, the SNES and SPC may end up waiting for each other in different parts of the protocol, freezing the system this may be incorrect — see note on discussion page.
Fortunately, there are thousands of programs for the SPC freely available online in the form of SPC files, solving half our problem. Since we’ll be needing the first two bytes at that location that we have been careful thus far not to overwritewe will first save snnes on the stack. Policies and guidelines Contact us. Here is the communication routine’s main loop, which sends a byte and snds for the SPC’s response, then updates the memory and counter values. Here, however, is a summary of the algorithm the SPC uses:.
Retrieved from ” https: Finally, we end the block and tell the SPC to start execution at the beginning of the SPC’s communication routine, resetting the protocol:.
Super NES Programming/Loading SPC700 programs
Since we’ll restore the first byte first, we push it last:. Thus the value that is snrs from a channel’s memory-mapped register may not be the value that was last written there.
We do this by playrr our communications routine to send no blocks, but rather immediately start execution at the given address:. This has the effect of restoring the timer state, as well as one DSP register.
Super NES Programming/Loading SPC programs – Wikibooks, open books for an open world
Rather than write this code repeatedly, we can put it in a macro, and the assembler will make the necessary substitutions:. This page was last edited on 23 Januaryat In other languages Add links. We have added a line to call a subroutine to load the SPC data, just before the graphics code from the initialization tutorial. If we tried to modify the above routine to do this, though, we would either need to know the address of the next block ahead of time or we would need to save the terminating byte of the previous block and send it with the next one.