fix unmapping problem #1
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Control registers for DMA, PWM etc. are accessed via memory-mapped IO. The structs which overlay the m'mapped regions use __attribute__ ((packed)) to ensure that there are no gaps between the structs fields. GCC < 5.1.0 assembles the write operation to a int32_t field inside a __attribute__ ((packed))'ed struct in the form str (write single 32-bit value to memory) whereas GCC >= 5.1.0 does something like strb #0 (write byte 0 of 32-bit value) strb #1 (write byte 1 of 32-bit value) strb richardghirst#2 (...) strb richardghirst#3 (...) The BCM2835's Clock Manager General Purpose Clock Control and Clock Manager General Purpose Clock Divisor Registers (both inside cm_pwm_t) only accept writes if bits 24-31 contain the value 0x5a, which obviously won't work if the 32 bits aren't written at once. As the struct already only contains 32-bit wide fields, packing them should not be necessary. For the sake of convenience, I also removed the attribute from the other m'mapped structs.
Fix hang when compiled with gcc >= 5.1.0
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This solves the memory unmapping problem. But are the LEDs intentionally staying lit? |
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Jun 20, 2021
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As discussed in jgarff#32 this patch solves an issue with memory unmapping.
I have to admit I am not proficient enough in C to fully understand what the issue exactly is and why this solves it, but it would be great if we could have this in your fork - as it happens to be the upstream for raspberry-pi 2 compatibility.
Also: Thanks a lot for your work, it did save me a lot of trouble :)