Difference between revisions of "PIC32"

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 +
Some things I've learned about PIC32MX and MZ.
 
==Tips==
 
==Tips==
−
===MX is not MZ===
+
===MX is not MZ is not C is not MM===
−
Essentially there are two distinct PIC32 architectures. MX and MZ. The reference manuals (Family Reference Manuals) that apply to MZ do not apply to MX. A simple thing to misunderstand for beginners. Use the reference manual that is mentioned in your Pic's particular datasheet.
+
For starters, there are two distinct PIC32 architectures. MX and MZ (let's forget about the rest). The reference manuals (Family Reference Manuals) that apply to MZ do not apply to MX. A simple thing to misunderstand for beginners. Use the reference manual that is mentioned in your Pic's particular datasheet.
−
===Pic32 can be Power Hungry===
+
 
 +
Then there is PIC32C (C == ARM Cortex), and some others...
 +
 
 +
===PIC32 can be Power Hungry===
 
Check your voltage regulator if you find that your code keeps resetting, when in debug mode. I found that my resets were due to not enough power. The more peripherals you turn on, the more power you will need. This is one reason why code will work, then suddenly fail after adding functionality (say turning on DMA, or a constant UART stream)
 
Check your voltage regulator if you find that your code keeps resetting, when in debug mode. I found that my resets were due to not enough power. The more peripherals you turn on, the more power you will need. This is one reason why code will work, then suddenly fail after adding functionality (say turning on DMA, or a constant UART stream)
 +
===Read Registers Whilst Debugging===
 +
If you put just a register macro, e.g. U1STA; or U1MODE; in the code, and even if nothing happens to that register, it can be read by hovering over it while debugging. Useful to just type out a number of registers in the code, and then pause, and check them while debugging.
 +
An example:
 +
/*U1MODE;
 +
U1STA;
 +
IFS1;
 +
IEC1;
 +
RCON;*/ //Comment them out, otherwise they will generate asm in disassembler.
 +
 +
===MPLAB X Tools - Debugger - Watches doesn't work for large arrays===
 +
The watch doesn't read the whole array. Export to CSV to see all values, or examine map file. MPLAB 5.25. Reference: https://www.microchip.com/forums/m790353.aspx
 +
 +
===Atomic Operations on bits===
 +
See:
 +
IFS4bits.DMA1IF = 0 //takes a few cycles, can cause problems
 +
IFS4CLR = _IFS4_DMA1IF_MASK //takes one cycle. better.
 +
 +
===Resets===
 +
====Dest and Source Sizes====
 +
Incorrect Dest and Source sizes for DMA can cause resets. It will register as POR and BOR, but it's due to for example, the source of SPIxBUF being set to size 10 bytes, (which is incorrect, SPIxBUF can only be 1,2 or 4 bytes depending on settings).
 +
====Insufficient Power====
 +
Self explanatory.
 +
====_ISR Invalid Parameters====
 +
If you have an ISR (interrupt), and you pass IPL5SRS. Everything is working fine, then you change that to IPL2SRS, and you are in a reset loop.
 +
Read the books mentioned below for more info. IPLxYYYY where x is 1-7 and YYYY is SRS or Soft. Not all combinations are possible.
 +
 +
===DMA===
 +
====DMA - If you CFORCE, and it finishes, you must CHEN again to CFORCE again====
 +
Subject.
 +
====Not all Pic32 have 16 bits of DMA memory====
 +
Earlier pics (PIC32MX440) only have 8 bits in DCHxSSIZ or DSIZ. If it only outputs 256 bytes, this is why. Check that register, because it's not mentioned anywhere else.
 +
====DMA Has Issues with editing a coherent buffer, maybe related to kseg1====
 +
Let's say you have a video buffer. 10000 bytes. You setup three for loops to edit the buffer at different increments. One might edit the first 8, then skip ahead to 24, edit that 8, then skip to 48 and edit that 8, etc... The second will edit the second 8 starting at 8, going to 16, and following a similar pattern as the previous. Finally you will have a third doing the same. What happens, is that the third overwrites everything with its values.
 +
 +
===Prefetch Cache (MZ)===
 +
====Cache can stop initialization of large variables when using them for DMA====
 +
Let's say you have a loop
 +
for(x=0,x<10000,x++){
 +
    array[x] = 0xFF;
 +
}
 +
If you have cache enabled (it's enabled by default on MZ) you will only get 6000 or so of the variables changed for DMA. If you go to debugging - watch - choose array[x] and export to csv, you will see all the values have 0xFF but the dma will output about 6000 of 0xFF and then 4000 of 0's or 1's. The solution is to disable the cache via http://web.archive.org/web/https;//microchipdeveloper.com/32bit:mz-cache-disable
 +
 +
Reference: http://web.archive.org/web/https://www.microchip.com/forums/m1116587.aspx
 +
 +
==Code==
 +
[[PIC32_Examples]] - scraps atm
 +
 
==Resources==
 
==Resources==
 +
===Family Reference Manuals===
 +
Start here. These will be your required reading for any peripheral. The data sheets will also be required. With these two in hand, you should be able to flip almost any bit needed. Make sure you get the Reference manual for your particular implementation (MX or MZ).
 
===Peripheral Library Examples===
 
===Peripheral Library Examples===
 
There are a number of well commented (unlike most garbage online) examples that are ideal for someone learning about setup of pic32 peripherals in the Peripheral Libraries Examples. Link: https://people.ece.cornell.edu/land/courses/ece4760/PIC32/PLIB_examples/plib_examples/
 
There are a number of well commented (unlike most garbage online) examples that are ideal for someone learning about setup of pic32 peripherals in the Peripheral Libraries Examples. Link: https://people.ece.cornell.edu/land/courses/ece4760/PIC32/PLIB_examples/plib_examples/
−
===Family Reference Manuals===
+
===Books===
−
These will be your required reading for any peripheral. The data sheets will also be required. With these two in hand, you should be able to flip almost any bit needed. Make sure you get the Reference manual for your particular implementation (MX or MZ).
+
 
 +
{{Electronics}}

Latest revision as of 07:23, 5 November 2019

Some things I've learned about PIC32MX and MZ.

Tips

MX is not MZ is not C is not MM

For starters, there are two distinct PIC32 architectures. MX and MZ (let's forget about the rest). The reference manuals (Family Reference Manuals) that apply to MZ do not apply to MX. A simple thing to misunderstand for beginners. Use the reference manual that is mentioned in your Pic's particular datasheet.

Then there is PIC32C (C == ARM Cortex), and some others...

PIC32 can be Power Hungry

Check your voltage regulator if you find that your code keeps resetting, when in debug mode. I found that my resets were due to not enough power. The more peripherals you turn on, the more power you will need. This is one reason why code will work, then suddenly fail after adding functionality (say turning on DMA, or a constant UART stream)

Read Registers Whilst Debugging

If you put just a register macro, e.g. U1STA; or U1MODE; in the code, and even if nothing happens to that register, it can be read by hovering over it while debugging. Useful to just type out a number of registers in the code, and then pause, and check them while debugging. An example: 

/*U1MODE;
U1STA;
IFS1;
IEC1;
RCON;*/ //Comment them out, otherwise they will generate asm in disassembler.

MPLAB X Tools - Debugger - Watches doesn't work for large arrays

The watch doesn't read the whole array. Export to CSV to see all values, or examine map file. MPLAB 5.25. Reference: https://www.microchip.com/forums/m790353.aspx

Atomic Operations on bits

See: 

IFS4bits.DMA1IF = 0 //takes a few cycles, can cause problems
IFS4CLR = _IFS4_DMA1IF_MASK //takes one cycle. better.

Resets

Dest and Source Sizes

Incorrect Dest and Source sizes for DMA can cause resets. It will register as POR and BOR, but it's due to for example, the source of SPIxBUF being set to size 10 bytes, (which is incorrect, SPIxBUF can only be 1,2 or 4 bytes depending on settings).

Insufficient Power

Self explanatory.

_ISR Invalid Parameters

If you have an ISR (interrupt), and you pass IPL5SRS. Everything is working fine, then you change that to IPL2SRS, and you are in a reset loop. Read the books mentioned below for more info. IPLxYYYY where x is 1-7 and YYYY is SRS or Soft. Not all combinations are possible.

DMA

DMA - If you CFORCE, and it finishes, you must CHEN again to CFORCE again

Subject.

Not all Pic32 have 16 bits of DMA memory

Earlier pics (PIC32MX440) only have 8 bits in DCHxSSIZ or DSIZ. If it only outputs 256 bytes, this is why. Check that register, because it's not mentioned anywhere else.

DMA Has Issues with editing a coherent buffer, maybe related to kseg1

Let's say you have a video buffer. 10000 bytes. You setup three for loops to edit the buffer at different increments. One might edit the first 8, then skip ahead to 24, edit that 8, then skip to 48 and edit that 8, etc... The second will edit the second 8 starting at 8, going to 16, and following a similar pattern as the previous. Finally you will have a third doing the same. What happens, is that the third overwrites everything with its values.

Prefetch Cache (MZ)

Cache can stop initialization of large variables when using them for DMA

Let's say you have a loop 

for(x=0,x<10000,x++){
    array[x] = 0xFF;
}

If you have cache enabled (it's enabled by default on MZ) you will only get 6000 or so of the variables changed for DMA. If you go to debugging - watch - choose array[x] and export to csv, you will see all the values have 0xFF but the dma will output about 6000 of 0xFF and then 4000 of 0's or 1's. The solution is to disable the cache via http://web.archive.org/web/https;//microchipdeveloper.com/32bit:mz-cache-disable

Reference: http://web.archive.org/web/https://www.microchip.com/forums/m1116587.aspx

Code

PIC32_Examples - scraps atm

Resources

Family Reference Manuals

Start here. These will be your required reading for any peripheral. The data sheets will also be required. With these two in hand, you should be able to flip almost any bit needed. Make sure you get the Reference manual for your particular implementation (MX or MZ).

Peripheral Library Examples

There are a number of well commented (unlike most garbage online) examples that are ideal for someone learning about setup of pic32 peripherals in the Peripheral Libraries Examples. Link: https://people.ece.cornell.edu/land/courses/ece4760/PIC32/PLIB_examples/plib_examples/

Books

Electronics
PCB
Microcontrollers
FPGAs
ICs
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