esp-develop-20210826

• Rebased on top of QEMU 6.1.0. Upgraded build dependencies, fixed breakage/deprecations.
• Added SDMMC (SD Host) peripheral emulation (#5).
• Added basic PSRAM emulation (#4). Either 2 MB or 4 MB of PSRAM can be added to the machine using -M command line option. "Himem" feature in ESP-IDF doesn't work yet, as only a simple linear cache mapping is supported.
• Two environment variables have been introduced for compatibility with existing versions of GDB. The upcoming toolchain release, esp-2021r2, will ship a version of GDB that fixes a number of issues observed on Xtensa architecture. This release of QEMU can work with the older toolchain releases, if the following environment variables are set. It can also benefit from the fixes in the new release of GDB, in this case these variables shouldn't be set.
  • If QEMU_XTENSA_CORE_REGS_ONLY=1 is set, QEMU will only send non-privileged registers to GDB. Setting this to 1 matches the behavior in previous versions of QEMU. Otherwise, all registers (including the privileged ones) will be sent.
  • If QEMU_XTENSA_COUNT_WINDOW_REGS=1 is set, a0-a15 registers (i.e. the current register window) will be sent to GDB. Setting this to 1 matches the behavior in the previous versions of QEMU. Otherwise, window registers will not be sent, and GDB will treat them as pseudo registers.
• Fixed DIO flash mode support (#16). Switching to DOUT mode is no longer necessary.
• Fixed handling of DP83848C PHYSTS register (#14).
• Fixed detection of ESP32 ECO3 version via APB_CTRL_DATE_REG.
• Fixed LACT timer interrupt emulation.
• Fixed switch fallthrough bugs in I2C emulation.
• Fixed race conditions in eFuse emulation.