Prior to this commit the USB CDC used the USB start-of-frame (SOF) IRQ to
regularly check if buffered data needed to be sent out to the USB host.
This wasted resources (CPU, power) if no data needed to be sent.
This commit changes how the USB CDC transmits buffered data:
- When new data is first available to send the data is queued immediately
on the USB IN endpoint, ready to be sent as soon as possible.
- Subsequent additions to the buffer (via usbd_cdc_try_tx()) will wait.
- When the low-level USB driver has finished sending out the data queued
in the USB IN endpoint it calls usbd_cdc_tx_ready() which immediately
queues any outstanding data, waiting for the next IN frame.
The benefits on this new approach are:
- SOF IRQ does not need to run continuously so device has a better chance
to sleep for longer, and be more responsive to other IRQs.
- Because SOF IRQ is off, current consumption is reduced by a small amount,
roughly 200uA when USB is connected (measured on PYBv1.0).
- CDC tx throughput (USB IN) on PYBv1.0 is about 2.3 faster (USB OUT is
unchanged).
- When USB is connected, Python code that is executing is slightly faster
because SOF IRQ no longer interrupts continuously.
- On F733 with USB HS, CDC tx throughput is about the same as prior to this
commit.
- On F733 with USB HS, Python code is about 5% faster because of no SOF.
As part of this refactor, the serial port should no longer echo initial
characters when the serial port is first opened (this only used to happen
rarely on USB FS, but on USB HS is was more evident).
The macros are MICROPY_HEAP_START and MICROPY_HEAP_END, and if not defined
by a board then the default values will be used (maximum heap from SRAM as
defined by linker symbols).
As part of this commit the SDRAM initialisation is moved to much earlier in
main() to potentially make it available to other peripherals and avoid
re-initialisation on soft-reboot. On boards with SDRAM enabled the heap
has been set to use that.
Configuring clocks is a critical operation and is best to avoid when
possible. If the clocks really need to be reset to the same values then
one can pass in a slightly higher value, eg 168000001 Hz to get 168MHz.
This ensures that on first boot the most optimal settings are used for the
voltage scaling and flash latency (for F7 MCUs).
This commit also provides more fine-grained control for the flash latency
settings.
Power and clock control is low-level functionality and it makes sense to
have it in a dedicated file, at least so it can be reused by other parts of
the code.
On F7s PLLSAI is used as a 48MHz clock source if the main PLL cannot
provide such a frequency, and on L4s PLLSAI1 is always used as a clock
source for the peripherals. This commit makes sure these PLLs are
re-enabled upon waking from stop mode so the peripherals work.
See issues #4022 and #4178 (L4 specific).
This part is functionally similar to STM32F767xx (they share a datasheet)
so support is generally comparable. When adding board support the
stm32f767_af.csv and stm32f767.ld should be used.
The HAL DMA functions enable SDMMC interrupts before fully resetting the
peripheral, and this can lead to a DTIMEOUT IRQ during the initialisation
of the DMA transfer, which then clears out the DMA state and leads to the
read/write not working at all. The DTIMEOUT is there from previous SDMMC
DMA transfers, even those that succeeded, and is of duration ~180 seconds,
which is 0xffffffff / 24MHz (default DTIMER value, and clock of
peripheral).
To work around this issue, fully reset the SDMMC peripheral before calling
the HAL SD DMA functions.
Fixes issue #4110.
The flash-IRQ handler is used to flush the storage cache, ie write
outstanding block data from RAM to flash. This is triggered by a timeout,
or by a direct call to flush all storage caches.
Prior to this commit, a timeout could trigger the cache flushing to occur
during the execution of a read/write to external SPI flash storage. In
such a case the storage subsystem would break down.
SPI storage transfers are already protected against USB IRQs, so by
changing the priority of the flash IRQ to that of the USB IRQ (what is
done in this commit) the SPI transfers can be protected against any
timeouts triggering a cache flush (the cache flush would be postponed until
after the transfer finished, but note that in the case of SPI writes the
timeout is rescheduled after the transfer finishes).
The handling of internal flash sync'ing needs to be changed to directly
call flash_bdev_irq_handler() sync may be called with the IRQ priority
already raised (eg when called from a USB MSC IRQ handler).
MCUs that have a PLLSAI can use it to generate a 48MHz clock for USB, SDIO
and RNG peripherals. In such cases the SYSCLK is not restricted to values
that allow the system PLL to generate 48MHz, but can be any frequency.
This patch allows such configurability for F7 MCUs, allowing the SYSCLK to
be set in 2MHz increments via machine.freq(). PLLSAI will only be enabled
if needed, and consumes about 1mA extra. This fine grained control of
frequency is useful to get accurate SPI baudrates, for example.
A recent version of arm-none-eabi-gcc (8.2.0) will warn about unused packed
attributes in USB_WritePacket and USB_ReadPacket. This patch suppresses
such warnings for this file only.
The aim here is to have spi.c contain the low-level SPI driver which is
independent (not fully but close) of MicroPython objects and methods, and
the higher-level bindings are separated out to pyb_spi.c and machine_spi.c.
