i.MX RT1060 Device Configuration Data (DCD) Generator

Crates.io docs.rs

The i.MX RT1050/1060 series of MCUs feature a ROM bootloader. As a part of the boot process, it interprets the Device Configuration Data (DCD) section in the firmware image to perform limited initialization and validation of peripheral registers, e.g. to set up external memory controllers, before any ARM instructions from the firmware image is run.

This crate allows you to generate a DCD binary (byte array) from its semantic description. This is useful e.g. in a build.rs script to generate a static variable to be linked to the firmware image. (Shameless plug: See static-include-bytes.)

What does the DCD do exactly?

Reference: i.MX RT1060 Reference Manual (rev. 3), ยง9.7.2 .

The DCD section in the firmware image is a serialized byte array of one or more commands:

Write command compression

Multiple Write commands with the same bit width and operation (i.e. write/clear/set) can be merged (sharing the same command header) to save some bytes. This might be helpful as there is a hardcoded byte length limit in the ROM (1768 bytes for RT1060, including headers).

This crate automatically performs this compression but does not enforce any byte size limit.

Valid Write command address ranges

The ROM only allows Write commands to a limited number of address ranges:

| Begin | End (inclusive) | Description | |-------------|-----------------|------------------------| | 0x400A4000 | 0x400A7FFF | IOMUX Control SNVS GPR | | 0x400A8000 | 0x400ABFFF | IOMUX Control SNVS | | 0x400AC000 | 0x400AFFFF | IOMUX Control GPR | | 0x401F8000 | 0x401FBFFF | IOMUX Control | | 0x400D8000 | 0x400DBFFF | CCM Analog | | 0x400FC000 | 0x400FFFFF | CCM | | 0x402F0000 | 0x402F3FFF | SEMC |

Writing to anywhere outside these ranges will cause the ROM to immediately abandon interpreting the rest of your DCD.

Again, this crate does not enforce any address range limitations.

Check command polling count

The Check command may specify one of the following:

Note that the ROM does not seem to limit the address range of Check commands.

Toy Example

```rust use imxrt_dcd::*;

let mut buf = std::io::Cursor::new(vec![]); let bytelen = serialize( &mut buf, &[ Command::Nop, Command::Write(Write { width: Width::B4, op: WriteOp::Write, address: 0x01234567, value: 0xdeadbeef, }), Command::Check(Check { width: Width::B2, cond: CheckCond::AnySet, address: 0x89abcdef, mask: 0x55aa55aa, count: Some(16), }), Command::Check(Check { width: Width::B1, cond: CheckCond::AnyClear, address: 0x89abcdef, mask: 0x55aa55aa, count: None, }), ], ) .expect("IO failure"); asserteq!(bytelen, 48); asserteq!( &buf.get_ref()[0..48], &[ // DCD header 0xD2, 0, 48, 0x41, // nop 0xC0, 0x00, 0x04, 0x00, // write 0xCC, 0, 12, 0x04, 0x01, 0x23, 0x45, 0x67, 0xde, 0xad, 0xbe, 0xef, // check with count 0xCF, 0, 16, 0x1a, 0x89, 0xab, 0xcd, 0xef, 0x55, 0xaa, 0x55, 0xaa, 0, 0, 0, 16, // check without 0xCF, 0, 12, 0x09, 0x89, 0xab, 0xcd, 0xef, 0x55, 0xaa, 0x55, 0xaa, ] ); ```