Match basic CMSIS functionality for v7m

[justinbalexander]

This first milestone will be to reproduce at least the same subset of functionality as CMSIS.

While the functionality will be the same, this will not be a translation of CMSIS but rather a fresh rewrite in Zig with a (hopefully) improved and expressive API.

Every function or register definition must be documented with the document number combined with the section and/or table where the information was found for cross-referencing purposes.

For example:

/// ARM DDI 0403E.b Section B3.2
/// Table B3-3
const SCS_BASE = 0xE000E000;
const SYSTICK_BASE = SCS_BASE + 0x010;
const NVIC_BASE = SCS_BASE + 0x100;
const SCB_BASE = SCS_BASE + 0xD00;
const MPU_BASE = SCS_BASE + 0xD90;
const SCS_DEBUG_BASE = SCS_BASE + 0xDF0;
const CACHE_MAINTENANCE_BASE = SCS_BASE + 0xF50;
const MCU_ID_BASE = SCS_BASE + 0xFD0;

The document number including the version is there.

The resulting function and/or register definition should match the architecture reference manual from which it was pulled. CMSIS changed some register names and this rewrite should follow the reference manuals exactly. If there is a deviation from this convention, it must be documented and justified in a comment.

A list of functionality that must be matched will be checked off here:

• Register Addresses
• Interrupts: enable/disable, priority masks
• Get special registers/ status registers
• Core instructions that require assembly (NOP, WFE, etc)
• Config file to select architecture
• Data and instruction cache control
• Memory Protection Unit
• "SysTick" aka Periodic Interval Timer
• Clock frequency?
• Tightly Coupled Memory

Further functionality will be filed as separate issues.