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The System Management Controller (SMC) is an 8051/8052 core inside the Southbridge. It manages the power sequencing, and is always active when the Xbox 360 has (standby or full) power applied. It controls the frontpanel, has a Realtime clock, decodes IR, manages temperatures, fans, DVDROM tray and a bunch of other things. It talks with the frontpanel board to set the LEDs. When the system is running, the kernel can communicate with the SMC, for example to query the realtime clock, open the dvd-tray etc.


Sending a Message

Communication between kernel and SMC happens over a bidirectional FIFO (at ea001080 / ea001090).
All messages and replies are 16 byte long and have the command id in the first byte.

void smc_send(void *msg)
      while (!(readl(0xea001084) & 4))    // wait for FIFO ready

      writel(4, 0xea001084);              // start message
      writesl(0xea001080, msg, 4);        // send 16 bytes
      writel(0, 0xea001084);              // end message

Receiving a Reply

Some messages have replies, which will be returned as 16 byte sequence similar to the message (they also have the command id in the first byte).

int smc_read_reply(void *msg)
      if (!(readl(0xea001094) & 4))       // do we have a reply?
              return 0;

      writel(4, 0xea001094);              // start reply
      readsl(0xea001090, msg, 4);         // read 16 bytes
      writel(0, 0xea001094);              // end reply
      return 1;

Command Messages

ID Len Example Purpose
0x82 2-3 "\x82\0x04\0x31\0\0\0\0\0\0\0\0\0\0\0\0\0" set standby/power
0x8c 3 "\x8c\0x01\0x00\0\0\0\0\0\0\0\0\0\0\0\0\0" set power led

Query Messages

ID Len Example Query Example Reply Purpose
0x01 1:6 "\x01\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 01 12 00 00 00 00 power on type
0x04 1:11 "\x04\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 04 602f 212223 01 00000000 real time clock
0x07 1:10 "\x07\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 07ff 241b 2fa4 2cfa 262c read temperature
0x0a 1:2 "\x0a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 0a 60 request tray state
0x0f 1:2 "\x0f\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 0f 54 request AV-Pack type
0x11 6:2 "\x11\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 11 02 read ana
0x12 1:6 "\x12\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 1241 0203 0000 request SMC version
0x16 1:2 "\x16\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 16 0f query IR access
0x17 1:2 "\x17\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" 17 00 request tilt state

Event Messages

ID Len Example Message Purpose
0x83 2 83 64 SMC Event