lpc213x/01 I/O latency

Development Boards MicroMod
1

Hello All.

Through my current project involving an LPC2134/01, I have experienced I/O latency, which I have not been able to find documented. Basically I am implementing an address/data-bus using fast GPIO.

The problem shows when I try this:

  FIO1CLR3=(BUS_CS)>>24; // Do chip select
  readVal=FIO1PIN2;      // Read value
  FIO1SET3=(BUS_CS)>>24; // Let go CS

readVal gets the wrong value, because it is read too early. If I add a NOP before reading the value, it works correctly:

  FIO1CLR3=(BUS_CS)>>24; // Do chip select
  asm("nop");            // Delay
  readVal=FIO1PIN2;      // Read value
  FIO1SET3=(BUS_CS)>>24; // Let go CS

This is running at 10MHz CPU clock. At higher frequencies I need another NOP or two.

The external device presents a latency of 12ns from CS low to data valid (measured with a scope). At 10MHz the NOP accounts for 100ns and the I/O instruction for 200ns. It makes sense that there is a delay from the output instruction is executed until the pin changes, and from the input pin changes until the register state is updated. However, I have not been able to find this documented anywhere.

Does anyone have a pointer to the documentation (data sheet or similar) that defines the maximum delay for input and output using fast GPIO on the LPC213x/01?

Thanks in advance

2

Come to think of it, would the instruction pipeline in the LPC affect this?