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SkeeterHawk
Joined: 16 Oct 2010
Posts: 45
Location: Florissant, CO
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| Generated Assembly General Question |
 Posted: Fri Apr 04, 2025 9:11 pm |
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Hello yet again, everyone.
I am still trying to get to the bottom of my issue with the SPI communications and have been going through the generated assembly line by line.
My question is pretty simple. I am trying to read the register addresses that are being used and one aspect is confusing to me.
| Code: | .................... SOSIF = 0; // Since it was set, clear it now so that we don't get stuck in here
0017E: BCF x8A.5 ; Since this says that it is 0x8A, this is the address for SFR SPI1INTF and clears bit #5, which is the SOSIF (Start of client select). This isn't really used right now, but is what I am using to derive that 0x?? is pointing to an SFR
.................... AddressIn = spi_xfer(SPI, 0xAA, 8); // Load the address register with the data that is on the SPI bus so we can see where we go from here
00180: CLRF 51B ; Addresses 51B - 51E are reserved for @SPIPREWRITE_1 in my Symbol file
00182: MOVLW AA ; This is the dummy data that I am trying to send when I only care about what I am reading, but I am sending this pattern to make sure that the TX buffer has something > 0 in it
00184: MOVLB 5 ; Bank 5
00186: MOVWF x64 ; This is the one that confuses me! SFR at address 0x064 is PMD4 (Peripheral Module Disable #4). This makes no sense to me
00188: MOVLB 0 ; Bank 0
0018A: RCALL 00B2 ; Call the SPI_XFER() Command (Below)
0018C: MOVF 501,W ; Address #501 in my Symbol list is @SCRATCH, so move this to the Working register
0018E: MOVFF 500,562 ; Move what was in the previous @SCRATCH register from my Symbol list to address 562 - 565 are for @SPI_XFER_1_32.P1 in the sym file |
Here is the code generated for the SPI_XFER() command to which I am adding lots of comments:
| Code: | 000B2: MOVF 51B,F ; Address 51B-51E is in the Symbol file as @SPIPREWRITE_1 and it is just cycling it through the Zero register
000B4: CLRF 51B ; Clearing it here
000B6: BZ 00BE ; Check for zero and go test the receive interrupt flag if it is
000B8: MOVF x80,W ; I believe that this is SFR address 0x080, which is SPI1RXB and moving it to the working register
000BA: MOVFF 564,81 ; Now it takes the data in the register in my Symbol file at @SPI_XFER_1_8.P2 and transfers it to the SFR at address 0x081 which is SPI1TXB
000BE: BTFSS 4B1.0 ; Test the PIR3 bit 0, which is SPI1RXIF
000C0: BRA 00BE ; Wait for it to be set
000C2: MOVFF 80,500 ; Now it wants to move what is in SFR register 0x080, which is SPI1RXB to my Symbol table @Scratch
000C6: RETURN 0 |
The point to all of this is that I believe that my communications are getting jacked up because the TXBE (Transmit Buffer Empty) bit is staying set, so I am just echoing the address that I was just sent instead of the 0xAA data that I am loading into the SPI_XFER command. From the generated assembly, it appears that the SPI1TXB register is being written with the data that is in address 564, but the calling routine is loading the data that I want to transmit into register x64. The Buffer Empty flag is refusing to clear.
I am using compiler version 5.114 on a PIC18F57Q84. Let me know if you need any more information, but I think that I have a pretty fundamental misunderstanding somewhere that doesn't require a bunch of code to make my post bigger. Thanks so much for your input!!
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Life is too short to only write code in assembly... |
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temtronic
Joined: 01 Jul 2010
Posts: 9450
Location: Greensville,Ontario
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| Posted: Sat Apr 05, 2025 5:53 am |
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don't have that PIC but...
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MOVLB 5 ; Bank 5
00186: MOVWF x64
.....
The PIC is now in bank #5, not the 'base' of Bank 0
would need to se the memory map to see what register it's dealing with |
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SkeeterHawk
Joined: 16 Oct 2010
Posts: 45
Location: Florissant, CO
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| Explanation of why the assembly works |
| Posted: Sun Apr 06, 2025 2:32 pm |
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Thank you for the reply, temtronic. I needed that "sanity check". You are absolutely right, and I am not sure why I didn't put this together myself, but I will explain it here in case it helps someone else with a fundamental misunderstanding as I had.
I believe that before the call it was using the bank select register to indirectly write the value into the register:
| Code: | 00182: MOVLW AA
00184: MOVLB 5
00186: MOVWF x64
00188: MOVLB 0
0018A: RCALL 00B2 |
So now 0xAA is in register at address 564. Note also that it returns it back to bank 0 before making the call.
Later in the SPI_XFER function, it directly pulls this data from the register to write to the transmit register:
| Code: | | 000BA: MOVFF 564,81 |
This part all makes sense now. Thanks again for you input, temtronic!
_________________
Life is too short to only write code in assembly... |
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temtronic
Joined: 01 Jul 2010
Posts: 9450
Location: Greensville,Ontario
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| Posted: Sun Apr 06, 2025 3:05 pm |
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tou're welcome...
somethings this old dinosaur remembers from the glory days of 16C84s and 15 minute coffee breaks while the UV eraser got rid of my mistakes...... |
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SkeeterHawk
Joined: 16 Oct 2010
Posts: 45
Location: Florissant, CO
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| Posted: Sun Apr 06, 2025 3:16 pm |
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| temtronic wrote: | tou're welcome...
somethings this old dinosaur remembers from the glory days of 16C84s and 15 minute coffee breaks while the UV eraser got rid of my mistakes...... |
LOL! I've still got my UV Eraser on my bench...got dust on it, thank God! That'll take ya back!...but I sure don't miss it. Flash is awesome!!
Thanks again!!
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