If both FS and HS USB peripherals are enabled for a board then the active
one used for the REPL will now be auto-detected, by checking to see if both
the DP and DM lines are actively pulled low. By default the code falls
back to use MICROPY_HW_USB_MAIN_DEV if nothing can be detected.
When going out of memory-mapped mode to do a control transfer to the QSPI
flash, the MPU settings must be changed to forbid access to the memory
mapped region. And any ongoing transfer (eg memory mapped continuous read)
must be aborted.
The Cortex-M7 CPU will do speculative loads from any memory location that
is not explicitly forbidden. This includes the QSPI memory-mapped region
starting at 0x90000000 and with size 256MiB. Speculative loads to this
QSPI region may 1) interfere with the QSPI peripheral registers (eg the
address register) if the QSPI is not in memory-mapped mode; 2) attempt to
access data outside the configured size of the QSPI flash when it is in
memory-mapped mode. Both of these scenarios will lead to issues with the
QSPI peripheral (eg Cortex bus lock up in scenario 2).
To prevent such speculative loads from interfering with the peripheral the
MPU is configured in this commit to restrict access to the QSPI mapped
region: when not memory mapped the entire region is forbidden; when memory
mapped only accesses to the valid flash size are permitted.
This fixes compiling for older architectures (e.g. armv5tej).
According to [1], the limit of R0-R7 for the STR and LDR instructions is
tied to the Thumb instruction set and not any specific processor
architectures.
[1]: http://www.keil.com/support/man/docs/armasm/armasm_dom1361289906890.htm
When compiled with hard float the system should enable FP access when it
starts or else FP instructions lead to a fault. But this minimal port does
not enable (or use) FP and so, to keep it minimal, switch to use soft
floating point. (This became an issue due to the recent commit
34c04d2319 which saves/restores FP registers
in the NLR state.)
Damien George
David Lechner
Paul m. p. P