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update comment and correct the size to 8+2

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hathach 2021-01-08 11:21:26 +07:00
parent 60620dca42
commit cc5dfd03cd
1 changed files with 8 additions and 5 deletions
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13
src/portable/microchip/samd/dcd_samd.c
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@ -39,11 +39,14 @@
static TU_ATTR_ALIGNED(4) UsbDeviceDescBank sram_registers[8][2];
// Setup packet is only 8 bytes in length. However under certain scenario,
// SAMD21 USB DMA controller is "suspected" to overwrite/overflow the setup_packet with 2 extra bytes.
// Which corrupt other variable and cause issue such as
// https://github.com/adafruit/circuitpython/issues/3912 (on macOS)
// Therefore we increase it to 12 bytes as walk-around until figuring out the root cause
static TU_ATTR_ALIGNED(4) uint8_t _setup_packet[8+4];
// USB DMA controller may decide to overwrite/overflow the buffer with
// 2 extra bytes of CRC. From datasheet's "Management of SETUP Transactions" section
// If the number of received data bytes is the maximum data payload specified by
// PCKSIZE.SIZE minus one, only the first CRC data is written to the data buffer.
// If the number of received data is equal or less than the data payload specified
// by PCKSIZE.SIZE minus two, both CRC data bytes are written to the data buffer.
// Therefore we will increase it to 10 bytes just to be safe
static TU_ATTR_ALIGNED(4) uint8_t _setup_packet[8+2];
// ready for receiving SETUP packet
static inline void prepare_setup(void)